You can use several words in query to find by all of them at the same time. In addition, if you are lucky search understands word forms and some synonyms. It supports search by title and author. Examples:

  • 305 — search for 305, most probably it will find blogs about the Round 305
  • andrew stankevich contests — search for words "andrew", "stankevich" and "contests" at the same time
  • user:mikemirzayanov title:testlib — search containing "testlib" in title by MikeMirzayanov
  • "vk cup" — use quotes to find phrase as is
  • title:educational — search in title

Results

1.
The Ultimate Topic List (with Resources, Problems and Templates)
By YouKn0wWho, 5 years ago, In English
The Ultimate Topic List (with Resources, Problems and Templates) This post took $4$ years to make. And this is the most significant thing that I have ever shared in my whole life. #### Story Hi, I have been doing CP for like $4$ years and from the very beginning what I have been feeling is a need for a comprehensive topic list that will contain all sorts of topics from easy to advanced with corresponding tutorials, problem lists and templates so that I wouldn't have to look at different sites, from here to there. So what do you do when you think something is missing from the world? Yeah, you create that thing! So here I am, sharing the ultimate topic list that you will need in CP. When I say that it took me $4$ years to make it, I genuinely mean it. I have been collecting them from the inception of my CP journey and yesterday I thought that it got its almost complete shape. You may not imagine the sheer excitement hidden under each of the characters of this post. #### Payment You can pay me just by upvoting this blog and by being a bet...
have fun while riding the boat.

Full text and comments »

  • Vote: I like it
  • +4383
  • Vote: I do not like it

2.
Codeforces Round #712
By Monogon, history, 5 years ago, In English
Codeforces Round #712 omg hi! I am pleased to invite you to participate in [contest:1503] and [contest:1504]! You will be given **6 problems** and **2 hours 15 minutes** to solve them. I'm happy to announce the theme of this round is déjà vu! I would like to thank the following people: - <a class="rated-user user-red" href="https://images.emojiterra.com/twitter/512px/1f921.png" title="The Entire Circus">antontrygubO_o</a> for accepting all of my problems <span style="color:white;">at gunpoint</span> - <a class="rated-user user-orange" href="/profile/Nika_Tamliani" title="Useless Tester Nika_Tamliani">Nika_Tamliani</a>, <a class="rated-user user-violet" href="/profile/arvindr9" title="Useless Tester arvindr9">arvindr9</a>, <a class="rated-user user-red" href="/profile/dorijanlendvaj" title="Useful Tester dorijanlendvaj">dorijanlendvaj</a>, <a class="rated-user user-blue" href="/profile/I_Love_YrNameCouldBeHere" title="Useful Tester I_Love_YrNameCouldBeHere">I_Love_YrNameCouldBeHere</a>, <a class="r...
luck, have fun!

Full text and comments »

  • Vote: I like it
  • +2866
  • Vote: I do not like it

3.
Rounding 2025
By KAN, 8 months ago, In English
Rounding 2025 Hi Codeforces! 2025 comes to an end. However square the year was, we held a number of rounds: 29 Div. 1 and 31 Div. 2-only contests, to be precise! Additionally, 18 Div. 3, 4 Div. 4, and 13 Educational rounds made the schedule even more congested. <img src="/predownloaded/c8/54/c854d6a423b830263449cca6ff841c8e4e02e024.png" style="width:1400px; float:center; margin: 1em 1em 1em 1em"/> December is not only the <strike>perfect</strike> [only](/blog/entry/149140?#comment-1332941) time to wrap the year, but also to celebrate and thank all the people who made this year possible. That's why I want to highlight with this post the people whose efforts shaped Codeforces contests. I'd like to say a huge thank you to every active community member who created and/or prepared problems for Codeforces rounds! Without your ideas and creativity, it would be impossible to hold so fun and interesting competitions. There are so many of you from every corner of the world, so that it's impossible...
Codeforces rounds! Without your ideas and creativity, it would be impossible to hold sofun and, problems for Codeforces rounds! Without your ideas and creativity, it would be impossible to hold sofun

Full text and comments »

  • Vote: I like it
  • +2264
  • Vote: I do not like it

4.
Codeforces celebrates its 15th anniversary!
By MikeMirzayanov, 19 months ago, In English
Codeforces celebrates its 15th anniversary! <img src="https://assets.codeforces.com/files/codeforces15.jpg" style="width:250px; float:right; margin: 0 1em 1em 1em;" /> Hi, Codeforces! Around this time, 15 years ago, I was deploying the first version of Codeforces on a server, registering my account, and writing the first post. 15 years have passed. Well, happy anniversary to us! For me, this is the most exciting adventure — full of ups and downs, hard work, and moments of joy. What's amazing is that it was never a lonely journey. I've always had caring and reliable friends by my side! That includes the Codeforces team, coordinators and problem writers, our partners in various events, all community members, and, of course, our sponsors — steadfast supporters and helpers. Look at what we've accomplished together! Here are some of the key metrics over the years. There seems to be plenty to celebrate! <center> <img src="https://assets.codeforces.com/files/15/01-submissions.png" class="resource" style="width:300px;"/>...
entertain — we want to try a different format and create a fun show from the community for the community, — we want to try a different format and create a fun show from the community for the community

Full text and comments »

  • Vote: I like it
  • +2311
  • Vote: I do not like it

5.
Goodbye 2019. Hello 2020!
By MikeMirzayanov, 7 years ago, In English
Goodbye 2019. Hello 2020! <img src="/predownloaded/85/58/8558df7ac8a1c33d501ea8fd9b18dd3d95886b90.png" style="width:290px; float:right; margin: 0 1.5em 1.5em 1.5em"/> I am happy to wish you a Happy New Year! I wish you a great, bright, interesting New Year! Just believe that it can become so: difficulties will be left behind, and ahead of you will be a joy of victories and discoveries. I wish all of us new interesting problems, records and achievements! Set new goals and be sure to try to achieve them! And do not go far, we will try to make your 2020 year more fun! I thank with all my heart for the contribution to the community of coordinators, problem writers, testers, and those who wrote interesting posts and comments. Many thanks to the sponsors, partners and customers: you help the community not to stand still, give the opportunity to hold interesting events. Thanks to all visitors to the website and just not indifferent. See you in the new year! &mdash; [user:MikeMirzayanov,2019-12-31]
go far, we will try to make your 2020 year more fun! I thank with all my heart for the, try to achieve them! And do not go far, we will try to make your 2020 year more fun!

Full text and comments »

  • Vote: I like it
  • +2750
  • Vote: I do not like it

6.
My opinion on how to practice competitive programming
By Radewoosh, history, 5 years ago, In English
My opinion on how to practice competitive programming I'm not very often replying to questions about how to practice, but as I'm getting enough of them (and I've just seen another blog about practicing) let me tell you about it. Of course, every time when you ask someone good about how to practice, he/she will reply to you to "solve a lot of problems" and that's true, there's no other way. Anyway, I've thought about it and actually I'm able to tell a bit more. I know some people, I've seen many people practicing (including me) and I have an opinion. Many people practice in some organized way. High schools organize IOI/OI training contests every Saturday, universities organize ICPC training contests once a week, people try by their own to solve three problems each day, websites host rounds and so on. Here's a secret: it's a sh*t. Yep, that's true. If you want to be really good and to make it happen you compete in a training once a week, you do it only to be able to make excuses "but I'm training so hard" when you see no progress. ...
your university? Of course, great idea — rivalry, some stress, fun with other people. If you, ; rivalry, some stress, fun with other people. If you are really practicing and trying to get better

Full text and comments »

  • Vote: I like it
  • +1899
  • Vote: I do not like it

7.
Codeforces Round #633
By McDic, history, 6 years ago, In English
Codeforces Round #633 **내가 돌아왔다!** (Hello, Codeforces!) I am thrilled to introduce you to [Codeforces Round #633](https://codeforces.me/contests/1338,1339). Followings are basic information: - This contest will take place on [contest_time:1338]. - The round is **rated for all participants** who can understand this announcement. There will be two divisions. - There are **5 problems** in each division and you will have **2 hours** to solve it. - Score distribution will be announced later. Followings are contributors: - **Authors**: [user:McDic,2020-04-10] (All Div.2 problems and Div.1 D), [user:tzuyu_chou,2020-04-10] (Div.1 E) - **Coordinator**: [user:antontrygubO_o,2020-04-10] - **Testers**: - **Phase 1** (When this round was supposed to be Div.2): [user:dorijanlendvaj,2020-04-10], [user:SoulTch,2020-04-10], [user:pajenegod,2020-04-10], [user:AryaPawn,2020-04-10], [user:Rahul,2020-04-10], [user:mcdx9524,2020-04-10], [user:300iq,2020-04-10], [user:Nemo,2020-04-10], [user:tfg,2020-04-10]...
Followings are some fun things:

Full text and comments »

  • Vote: I like it
  • +1622
  • Vote: I do not like it

8.
Good Bye 2019
By antontrygubO_o, 7 years ago, In English
Good Bye 2019 Hello again, Codeforces! We are glad to invite you to <s>Mathforces</s> <s>Thinkforces</s> [Good Bye 2019](https://codeforces.me/contests/1270), which will take place on [contest_time:1270]. Some information about the round: <ul> <li>Rated for all participants!</li> <li>3 hours!</li> <li> <strong> No subtasks! </strong> </li> <li>There will be an <strong> interactive problem </strong> in this round. You can read the guide for interactive problems [here](https://codeforces.me/blog/entry/45307)</li> <li> Editorial will be published right after the system testing </li> </ul> All problems in this round were prepared by us, [user:antontrygubO_o,2019-12-28] and [user:kefaa2,2019-12-28]. We worked on this round for a long time and tried to make all the problems very interesting. We hope that you will enjoy the round! We would like to thank: <ul> <li> [user:arsijo,2019-12-24] for coordination of the round </li> <li> [user:GandalfTheGrey,2019-12-24] fo...
making this year so fun! , so fun! The number of the problems and point distribution will be announced, Good luck and have fun!

Full text and comments »

Announcement of Good Bye 2019
  • Vote: I like it
  • +1517
  • Vote: I do not like it

9.
Good Bye 2015
By Errichto, 11 years ago, In English
Good Bye 2015 Hi everybody. The last round of the 2015 will take place on the 30-th of December ([starting time](http://www.timeanddate.com/worldclock/fixedtime.html?day=30&month=12&year=2015&hour=18&min=5&sec=0&p1=166)). The contest will last 3 hours. It won't be a usual round. Both divisions will compete together. You will get 8 problems to solve in 3 hours. Points will decrease slower than usually &mdash; otherwise you would get eps for solving a problem at the end. Scoring will be announced just before a contest. So will the speed of the points/minute loss. My goal was to provide you a diverse problemset with interesting problems for all contestants. During a contest you should consider reading not only the next problem but the few next ones. You will get this round thanks to work of many people. I am a problem setter. [user:GlebsHP,2015-12-28] helps me with everything (a lot). [user:AlexFetisov,2015-12-29], [user:johnasselta,2015-12-29] and [user:Zlobober,2015-12-29] are t...
by the way. You will help him, won't you? I wish you great fun and no frustrating bugs, I wish you great fun and no frustrating bugs. Looking forward to seeing you!

Full text and comments »

Announcement of Good Bye 2015
  • Vote: I like it
  • +1387
  • Vote: I do not like it

10.
Corruption, Cheating at ICPC Yinchuan
By NXIST_buster, history, 5 years ago, In English
Corruption, Cheating at ICPC Yinchuan This blog is about Corruption and Cheating at ICPC YinchuanRegional. ICPC Yinchuan Regional is one of the ICPC regional contests for students competing in the geographic area of Asia East Continent. I. Background: General Info ------------------ Ningxia Institute of Science of Technology, or NXIST is a higher education institute in China. Since 2019, NXIST has held two regional contests. The and both were considered by many participants as jokes, yet until today participants are unaware of the NXIST's extent of evil. Zhihu is a Chinese website similar to Quora, and I will refer to this website for information. II. Background: Before 2021 ------------------ Regional competitions in China consists of two stages: The online selection contest and the onsite regional contest. As there are many contestants in China, the online contest is considered serious and rules are usually strictly enforced, with entire universities where some participant cheats disqualified from attend...
"Just For Fun" and these teams are official. These teams were later awarded medals from the contest, , yet NXIST later said that the stars were "Just For Fun" and these teams are official. These teams, I know that maybe things isn't getting better after all these years of NXIST makingfun of ICPC

Full text and comments »

  • Vote: I like it
  • +1685
  • Vote: I do not like it

11.
On AI ruining "solving math problems with computer"
By Um_nik, history, 2 years ago, In English
On AI ruining "solving math problems with computer" You all went crazy. Instead of arguing with every opinion separately, I just want to ask one question: Why are you doing competitive programming? Is it to get to 1600 rating and put it on the resume? If so, please use AI, cheat, and do everything possible to get to 1600 as soon as possible and get the f**k out of this platform. And if you are (not) a normal person and do competitive programming because it is fun to solve problems, do you think it is fun to copy the problem statement into an AI model prompt and then copy the code it spews to submit? And why do you assume that everyone else will do that if there will be such an opportunity? The same goes for cheaters. Yes, some people do not do this as a sport, for fun. Why do you care? I do think that AI is ruining competitive programming. By proxy. And that proxy is all of you who are running around yelling "We will all die, somebody do something about AI". I have seen a couple of comments saying "authors/coordinators must make s...
platform. And if you are (not) a normal person and do competitive programming because it isfun to, programming because it is fun to solve problems, do you think it is fun to copy the problem statement into an, , I'm doing this FOR FUN., . STOP THIS. You are forgetting that all of this was for fun in the first place. Competitive programming, I hope this can be a wake-up call. A chance to remember that this was supposed to be afun activity

Full text and comments »

  • Vote: I like it
  • +1199
  • Vote: I do not like it

12.
Codeforces Round #715
By Kuroni, history, 5 years ago, In English
Codeforces Round #715 <p style="text-align: right;"> <i> "Love" is a violent word.<br> "I love that about you..." Doesn't that just mean "If that changed, I wouldn't love you anymore?"<br> "Love" is a word that binds you.<br> — Touko Nanami — </i> </p> Hi Codeforces! [user:Ari,2021-04-13] and I are pleased to invite you to participate in [contest:1508] and [contest:1509], which will be held at [contest_time:1508]. Each division will have **6 problems** and **2 hours and 15 minutes** to solve them. Big thanks to the following people: - Sir [user:antontrygubO_o,2021-04-13] for being an amazing coordinator; the round wouldn't happen without you ❤️ - [user:Scrubpai,2021-04-13], [user:1-gon,2021-04-13], [user:hugopm,2021-04-13], [user:tfg,2021-04-13], [user:dorijanlendvaj,2021-04-13], [user:xuanquang1999,2021-04-13], [user:300iq,2021-04-13], [user:Mike4235,2021-04-13], [user:Luminal,2021-04-13], [user:QuangBuiYT,2021-04-13], [user:jamienguyen,2021-04-13], [user:Pichu,2021-04-13], [user:ch...
! Good luck have fun to everyone!

Full text and comments »

  • Vote: I like it
  • +1371
  • Vote: I do not like it

13.
Testing Round 20 [Communication Problems]
By Proof_by_QED, history, 10 months ago, In English
Testing Round 20 [Communication Problems] Hello Codeforces. We are introducing a new type of problem which may appear in future Codeforces rounds, called Communication problems! In these problems, your program would be ran twice, with different input and output formats between the runs. All variables stored in the memory will be lost between runs. However, the information given to you on the first run may be important to you for completing the second run correctly. Therefore, one of the key challenges in these types of problems would be to find a way to use the limited amount of output you are given in the first run to communicate information to the second run. Below shows a flowchart. <center> <br/> <img src="https://i.ibb.co/JWMFpyfY/a-1.png" alt="2025-09-06-12-40-07" border="0" /> <br/> Flowchart for communication problems </center> In these problems, time and memory limits for both runs would be kept separately. For example, if a problem has a time limit of $2$ seconds, you will only get the Time Limit E...
problems. Of course, this round will be unrated. Good luck, and I hope you will havefun with the new, will have fun with the new type of problem!

Full text and comments »

  • Vote: I like it
  • +1572
  • Vote: I do not like it

14.
Codeforces Global Round 12
By Monogon, history, 6 years ago, In English
Codeforces Global Round 12 <img src="/predownloaded/2e/e2/2ee2f0f95f05aae6ca6f47812dae2dc2aabf277b.png" style="width:200px; float:right; margin: 0 1em 1em 1em"/> ¡Buenos días! (That's Spanish for "what's up homies") On [contest_time:1450] we will host [contest:1450]. It is the sixth round of a 2020 series of [Codeforces Global Rounds](/blog/entry/65002). The rounds are open and rated for everybody. The prizes for this round: - 30 best participants get a t-shirt. - 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive. The prizes for the 6-round series in 2020: - In each round top-100 participants get points according to the table. - The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest. - The best 20 participants over all series get sweatshirts and place certificates. Thanks to XTX, which in 2020 supported the global rounds initiative! The problems were written and prepared by smart Cu...
**UPD**: Here's the score distribution. Good luck, have fun!, , to each according to his needs! **UPD**: Here's the score distribution. Good luck, havefun

Full text and comments »

Announcement of Codeforces Global Round 12
  • Vote: I like it
  • +1239
  • Vote: I do not like it

15.
Codeforces Round #638 (Div. 2)
By FieryPhoenix, 6 years ago, In English
Codeforces Round #638 (Div. 2) Hi Codeforces! I’m thrilled to invite you to [contest:1348], which will take place on [contest_time:1348]. It's rated! There will be **6 problems**, and you will have **2.5 hours** to solve them. All the problems are written and prepared by me. Huge thank you to everyone who made this round possible: - [user:adedalic,2020-04-28] for awesome coordination, guidance, advice, and more <3 - [user:dragonslayerintraining,2020-04-28] for extensive testing, feedback, and buffing tests - [user:pikmike,2020-04-28], [user:walnutwaldo20,2020-04-28], [user:Benq,2020-04-28], [user:hocky,2020-04-28], [user:Geothermal,2020-04-28], [user:isaf27,2020-04-28], [user:McDic,2020-04-28], [user:bfs.07,2020-04-28], [user:iankury,2020-04-28], [user:songsinger,2020-04-28], [user:Agnimandur,2020-04-28], [user:dcshin,2020-04-28], [user:chrome,2020-04-28], [user:Rods,2020-04-29], [user:brian,2020-04-29], and [user:HAEtaRhoEta,2020-04-30] for taking the time to test and provide invaluable advice ...
problems on Polygon is fun!)

Full text and comments »

  • Vote: I like it
  • +1358
  • Vote: I do not like it

16.
Codeforces Raif Round 1 [Div. 1 + Div. 2]
By errorgorn, 6 years ago, In English
Codeforces Raif Round 1 [Div. 1 + Div. 2] Hello, Codeforces! Welcome to the [contest:1428] supported by Raiffeisenbank, that will start on [contest_time:1428]. **It will be a combined rated round for both divisions. Note that the start time is unusual.** All problems were authored and prepared by [user:bensonlzl,2020-10-15], [user:oolimry,2020-10-15], [user:errorgorn,2020-10-15], [user:dvdg6566,2020-10-15], [user:shenxy13,2020-10-15]. [user:Ari,2020-10-15] gato to: - [user:isaf27,2019-05-10] and [user:KAN,2020-10-15] for round coordination and help with preparation - [user:zhangguangxuan99,2020-10-15] for being epic IOI trainer <3 - Our army of testers: [user:Ari,2020-10-15], [user:KAN,2020-10-15], [user:Monogon,2020-10-15], [user:Prabowo,2020-10-15], [user:SYY,2020-10-15], [user:SleepyShashwat,2020-10-15], [user:TeaTime,2020-10-15], [user:Tlatoani,2020-10-15], [user:_rs_,2020-10-15], [user:agul,2020-10-15], [user:cstuart,2020-10-15], [user:dantoh,2020-10-15], [user:jhkoh,2020-10-15], [user:kai824,2020-10-15]...
interesting! Good luck, have fun and we wish everyone high ratings!, luck, have fun and we wish everyone high ratings! The scoring distribution will be announced

Full text and comments »

  • Vote: I like it
  • +1254
  • Vote: I do not like it

17.
Codeforces: summing up 2016 year
By MikeMirzayanov, 10 years ago, translation, In English
Codeforces: summing up 2016 year <center> <img src="http://assets.codeforces.com/images/Happy-New-Year-HD-Wallpapers.jpg"/> </center> Somehow it turns out that for me, each coming the New Year means more and more. This is an excellent opportunity to take stock, to breathe fresh air and to go through a kind of catharsis. This is a rare opportunity to be with the family, dress up in Santa Claus and just have fun. Holidays give me a clear criterion that I do the right things. If during the holidays, I begin to think about it, to recall some deferred ideas, eager to implement something new. So I’m doing right things. My things. And now exactly the same as in several recent years: during New Year holidays I write code for Codeforces, trying new technology or simply I’m making minor changes in testlib. It is necessary to me: at this moment are no deadlines, do not press the obligation. Just now, at 3 am, I can not break away from being able to do something new. I would like to take a moment and realize that spun in ...
is a rare opportunity to be with the family, dress up in Santa Claus and just havefun. Holidays, rare opportunity to be with the family, dress up in Santa Claus and just have fun., short, we have a fun live. The system load become higher, large number of improvements have been made

Full text and comments »

  • Vote: I like it
  • +1405
  • Vote: I do not like it

18.
My strategy at AtCoder & CS Academy
By tourist, 9 years ago, In English
My strategy at AtCoder & CS Academy There's been much controversy lately about the late submission strategy not penalized by scoring systems of AtCoder and CS Academy. Most of the relevant discussion happened earlier at http://codeforces.me/blog/entry/53431 and http://codeforces.me/blog/entry/53449. I have a lot of thoughts on the topic, so I've decided to share them in a separate blog post. I really like the strategic part of programming competitions. Of course, problem solving is more important. But every contest consists of multiple problems, so there has to be a way of comparing participants which performed better at different problems. There's a huge variety of scoring rules, and I find it truly amusing. The "submit after solving all problems" strategy looks widely attributed to me now, mostly due to [user:Petr,2017-07-24]'s remarks regarding my participation in AtCoder contests. In my opinion, it's wrong for multiple reasons. A closer five-word description of my strategy is "implement after solvin...
Have fun!

Full text and comments »

  • Vote: I like it
  • +972
  • Vote: I do not like it

19.
How to practice Competitive Programming [Um_nik version]
By Um_nik, history, 5 years ago, In English
How to practice Competitive Programming [Um_nik version] CP is about solving problems fast. And as absurd as it may sound, I believe that <span style="color:blue">SOLVE</span> and <span style="color:red">FAST</span> are very different and almost independent parts, and you need to practice them separately. Let’s look at some <span style="color:red">contest</span>, like a CodeForces round. For the sake of simplicity let’s assume that every problem has some *difficulty*, which is a numerical value denoting how hard it is, bigger values correspond to harder problems (it is not true, but it is an ok-ish approximation, at least if we consider subjective difficulty for a fixed person). Contests are made for a wide range of participants, and problemsetters strive to make contests interesting for a wide range of participants, which means having a *smooth difficulty gradient*. Well... as smooth as it is possible with 5-6 problems. <spoiler summary="Graph 1"> ![ ](https://s3.us-west-2.amazonaws.com/secure.notion-static.com/677e0ae2-a8df-4874-aff...
good to keep you in competitive shape. Also participating in contests is just fun, that’s also very

Full text and comments »

  • Vote: I like it
  • +1117
  • Vote: I do not like it

20.
I compiled a list of almost all useful blogs ever published on Codeforces [update: till 09.06.2021]
By parveen1981, history, 5 years ago, In English
I compiled a list of almost all useful blogs ever published on Codeforces [update: till 09.06.2021] <h3 style="color:red">If there are any blogs that I have missed, please tell in the comment section. Thank you.</h3> # Mathematics Stuff - [Number Theory in Competitive Programming [Tutorial]](https://codeforces.me/blog/entry/46620) - [Number of points on Convex hull with lattice points](https://codeforces.me/blog/entry/62183) - [FFT, big modulos, precision errors.](https://codeforces.me/blog/entry/48465) - [Number of ways between two vertices](https://codeforces.me/blog/entry/19078) - [Mathematics For Competitive Programming](https://codeforces.me/blog/entry/76938) - [FFT and NTT](https://codeforces.me/blog/entry/19862) - [Burnside Lemma](https://codeforces.me/blog/entry/51272) - [Number of positive integral solutions of equation 1/x+1/y=1/n!](https://codeforces.me/blog/entry/76836) - [On burnside (again)](https://codeforces.me/blog/entry/64860) - [Simple but often unknown theorems/lemmas/formula? Do you know?](https://codeforces.me/blog/entry/55912) - [Probabili...
# Have Some Fun - [The Mysterious Nature of Modern Cults on CF — A Documentation](https

Full text and comments »

  • Vote: I like it
  • +1500
  • Vote: I do not like it

21.
Codeforces Round #300 (with prizes!)
By Endagorion, 11 years ago, In English
Codeforces Round #300 (with prizes!) Hello, Codeforces! [On Sunday, April 26th at 19:00 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?day=26&month=4&year=2015&hour=19&min=0&sec=0&p1=166) the 300'th regular Codeforces Round will take place. I would like to congratulate all Codeforces members and administration on this remarkable milestone. The platform has grown hugely in size and quality since its foundation, has hosted lots of exciting competitions, and has been providing the opportunity to everyone to hone their problem solving and algorithmic mastery. For this we thank the Codeforces platform creator [user:MikeMirzayanov,2015-04-24] and all the Codeforces crew. Keep up the incredible job, guys! That being said, I'm excited to announce that the problems on the jubilee three-hundredth Codeforces Round will be set by me, Mikhail Tikhomirov ([user:Endagorion,2015-04-24]). You may remember the past rounds with my problems: [#99](http://codeforces.me/contests/138,139), [#109](http://codeforces.me/contest...
come back to compete for the prizes and for the fun! **UPD**: there will be **8** problems. The, That's it. Mark your calendars and come back to compete for the prizes and for thefun!

Full text and comments »

Announcement of Codeforces Round 300
  • Vote: I like it
  • +1212
  • Vote: I do not like it

22.
Codeforces Round #722
By AmShZ, history, 5 years ago, In English
Codeforces Round #722 Hi Codeforces! [user:Dio,2021-05-22], [user:Keshi,2021-05-22], [user:Tet,2021-05-22], [user:alireza_kaviani,2021-05-22], [user:-Zeus-,2021-05-22], [user:alishahali1382,2021-05-22] and I are delighted to invite you to participate in [contest:1528] and [contest:1529], which will be held at [contest_time:1528]. Each division will have **6 problems** and **2 hours and 15 minutes** to solve them. The curse has finally been lifted! We are proud to announce that [user:antontrygubO_o,2021-05-22] didn't reject even a single task from the Div. 1 part! Huge thanks to the following people: - [user:antontrygubO_o,2021-05-22] for being an outstanding coordinator; This round wouldn't have happened if it weren't for him. - Our ever-growing army of testers [user:gamegame,2021-05-22], [user:Amoo_Safar,2021-05-22], [user:Atreus,2021-05-22], [user:dorijanlendvaj,2021-05-22], [user:aarr,2021-05-22], [user:1-gon,2021-05-22], [user:EnEm,2021-05-22], [user:N.N_2004,2021-05-22], [user:AaParsa,20...
luck have fun to everyone!

Full text and comments »

  • Vote: I like it
  • +1145
  • Vote: I do not like it

23.
Codeforces Round #666
By atoiz, history, 6 years ago, In English
Codeforces Round #666 ![ ](/predownloaded/eb/3a/eb3ab0b4aa33c4881f4a8cd4084e9809c4b1f9b7.png) (Translation: Hello) We are very happy to invite you to take part in our contest, [contest:1396] and [contest:1397]. The contest starts on [contest_time:1396] and lasts **2 hours**. In both divisions, there will be **5 problems** for you to solve. The problems were authored and prepared by [user:Maripium,2020-08-28], [user:DatVu,2020-08-28], [user:MofK,2020-08-28], and me. We are very grateful and would like to sincerely thank the following people for their assistance in preparing the round: - [user:300iq,2020-08-28] for coordinating our round and for reviewing and helping us with the problems. - [user:minhtung04042001,2020-08-28], [user:TomOwO,2020-08-28], [user:EntityIT,2020-08-28] for their problem ideas and for helping us prepare the problemset. - [user:codeveloppy,2020-08-28], [user:lolicon234,2020-08-28], [user:DeadlyCritic,2020-08-28], [user:growup974,2020-08-28], [user:VietCT,2020-08-28...
Good luck, have fun!

Full text and comments »

  • Vote: I like it
  • +1146
  • Vote: I do not like it

24.
Hello 2026
By wangmarui, history, 8 months ago, In English
Hello 2026 Happy new year, Codeforces! We are glad to invite you to take part in [contest:2183], which will start on [contest_time:2183]. You will be given **9 problems** and **3 hours** to solve them. **At least one problem will be interactive**, so please make sure to read the [guide for interactive problems](https://codeforces.me/blog/entry/45307) before the contest. This round is open and rated for everyone. Problems are authored by [user:wangmarui,2025-12-23], [user:Gold14526,2025-12-23], [user:Hoks_,2025-12-23], [user:Neil_Qian,2025-12-23], [user:Network_Error,2025-12-23], [user:jiazhichen844,2025-12-23] and [user:xvchongyv,2025-12-23]. We would like to thank: - [user:Um_Nik,2025-12-23] for pre-reviewing the round. - [user:Proof_by_QED,2025-12-23] for his wonderful coordination. - [user:Alexdat2000,2025-12-23] for Russian translation. - [user:Geothermal,2025-12-23], [user:StarSilk,2025-12-23], and [user:Dominater069,2025-12-23] for nutella testing. - [user:Mindeve...
Good Luck & Have Fun!

Full text and comments »

Announcement of Hello 2026
  • Vote: I like it
  • +1039
  • Vote: I do not like it

25.
Pro Tips - get them while they are free
By Um_nik, history, 3 years ago, In English
Pro Tips - get them while they are free More tips to use while studying under my tutoring [here](https://um-nik.notion.site/Pro-Tips-8b923b0dc7c94770824bdf4184afc43c). ## Stop caring about the rating Unless there are prizes involved, your position in the standings makes no difference. I can feel awful after winning a contest if I know that I could solve one more problem. Or I can feel OK losing a bunch of rating points knowing that I solved everything I could.  Because rating is just a number. It is highly volatile and it depends on other people, not only on your skill. But solving problems is totally up to you. And you should evaluate yourself not based on some random metric, but on your honest feeling whether you performed up to your expectations. Your sense of self should be under your control, don't get hung up on some imaginary value, you cannot reduce your progress to a single number. ## Don't use more than one account Rating is just a number. Do not be afraid to lose your colour. You’ll get it back in no t...
beginners to get into problem setting. It is also a fun way of getting familiar with some new topic, into problem setting. It is also a fun way of getting familiar with some new topic, even if you don't

Full text and comments »

  • Vote: I like it
  • +1119
  • Vote: I do not like it

26.
Codeforces Global Round 11
By dario2994, 6 years ago, In English
Codeforces Global Round 11 <img src="/predownloaded/2e/e2/2ee2f0f95f05aae6ca6f47812dae2dc2aabf277b.png" style="width:200px; float:right; margin: 0 1em 1em 1em"/> Hi! On [contest_time:1427] we will host [contest:1427]. This is the fifth round of the 2020 series of [Codeforces Global Rounds](https://codeforces.me/blog/entry/65002). The rounds are open and rated for everybody. The prizes for this round are as follows: - 30 best participants get a t-shirt. - 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive. The prizes for the 6-round series in 2020: - In each round top-100 participants get points according to the [table](https://pastebin.com/QT5sXEaT). - The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest. - The best 20 participants over all series get sweatshirts and place certificates. Thanks to XTX, which in 2020 supported the global rounds initiative! Problems for this round ar...
I hope you will have fun solving the problems!

Full text and comments »

Announcement of Codeforces Global Round 11
  • Vote: I like it
  • +1025
  • Vote: I do not like it

27.
Codeforces Round #556
By mnbvmar, 7 years ago, In English
Codeforces Round #556 Hi Codeforces! I'm so happy to invite you to [contest:1149] and [contest:1150]! The rounds will be held on [contest_time:1149]. The round will be rated for both divisions. (At least that's what I've been told!) The problems were written and prepared by me. Thanks to [user:300iq,2019-04-27] for the round coordination, and to [user:Radewoosh,2019-04-27] for his invaluable help with choosing the problemset and testing the problems! Also, I want to give a shout-out to [user:MikeMirzayanov,2019-04-27] for his amazing Codeforces and Polygon platforms! ![ ](http://students.mimuw.edu.pl/~ms360974/stuff/tab-bar2.png) _My browser's tab bar, right now._ You'll work on **5** problems, and you will have **2** hours to solve them. The scoring distribution will be revealed closer to the round. ~~~~~ def get_end_remark(): return random.choice([ "Wish everyone high ratings!", "Good luck!", "Have fun!", "Please, read all the problems!"]) ~~~...
ratings!", "Good luck!", "Have fun!", "Please, read all the problems, !", "Good luck!", "Have fun!", "Please, read all the problems!"]) ~~~~~

Full text and comments »

  • Vote: I like it
  • +1064
  • Vote: I do not like it

28.
On Problems vs. Questions in Competitive Programming: My solution
By Ari, history, 5 years ago, In English
On Problems vs. Questions in Competitive Programming: My solution _TL;DR: The most reasonable solution to the problems vs. questions debate is to use none of the currently accepted terms._ As we have seen many times, particularly over the past few days, the task of assigning a label to the activities we perform as competitive programmers is a bigger problem than one might think at first. Time and time again we have seen people questioning what we should call our activities, often to the point of eliciting some rather harsh responses. To give some context to this discussion, I will focus on two of the terms that members of the community have adopted over the years, _problems_ and _questions_. (Sorry task lovers! You have some fine points for sure, we frequently talk about subtasks rather than subproblems or subquestions after all :P). All quotations here are posted anonymously, but if you want to claim ownership of one of them or have one removed, just tell me. If you are familiar with the arguments, feel free to skip to the final section of the...
fun of it. Indian English is different from American English or British English, but it's just that

Full text and comments »

  • Vote: I like it
  • +1178
  • Vote: I do not like it

29.
(The Ultimate) Code Library
By YouKn0wWho, 5 years ago, In English
(The Ultimate) Code Library Hey everyone, I am sharing my personal code library where I compiled **almost all** the important templates that you will need in CP (saying almost just for courtesy). Most of the codes are originally written by me and some of them are collected from others but modified in a cleaner way. Link: [https://github.com/ShahjalalShohag/code-library](https://github.com/ShahjalalShohag/code-library) It took me around 4 years to complete the list. Maybe each line is just a line to you but to me it tells a story of the excitements I had while learning those stuffs, the sleepless but fun nights I had to seek knowledge. ###### Why am I sharing this library? - Just so that your learning path becomes a bit smoother. - Knowledge hidden inside my head or codes in a private code-library will be useless when I am dead, so it's better to share those among people before I die. Also, you can make me happy(as in to pay me) just by upvoting this blog and giving a star to the repository. I beli...
tells a story of the excitements I had while learning those stuffs, the sleepless butfun nights I

Full text and comments »

  • Vote: I like it
  • +1334
  • Vote: I do not like it

30.
Codeforces Round 591 (and Technocup — Elimination Round 1)
By arsijo, 7 years ago, translation, In English
Codeforces Round 591 (and Technocup — Elimination Round 1) Hi all! This weekend, on [contest_time:1223] we will hold Codeforces Round 591. It is based on problems of Technocup 2020 Elimination Round 1 that will be held at the same time. Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at <a href="https://technocup.mail.ru/">Technocup 2020 website</a> and take part in the Elimination Round. Div. 1 and Div.2 editions are open and rated for everyone. Register and enjoy the contests! The Elimination Round authors are [user:BledDest,2019-10-06], [user:MikeMirzayanov,2019-10-06], [user:Ne0n25,2019-10-06], [user:PikMike,2019-10-06], [user:Roms,2019-10-06], [user:adedalic,2019-10-06] and me. This round would also be not possible without the help of our testers: [user:KAN,2019-10-06], [user:chemthan,2019-10-06], [user:gisp_zjz,2019-10-06], [user:Kallaseldor,2019-10-06], [user:JeffreyHo,2019-10-06], [user:danya.smelskiy,2019-10-06], [user:Juve45,2019-10-06], thank you...
Have fun!

Full text and comments »

  • Vote: I like it
  • +1254
  • Vote: I do not like it

31.
Codeforces: Results of 2017
By MikeMirzayanov, 9 years ago, translation, In English
Codeforces: Results of 2017 <img src="/predownloaded/e4/09/e40915ee54c5991b91098756a90270d94be893b3.jpg"/> Happy New Year, Codeforces! I hasten to wish the whole community (and including me) correct programs, sudden insights, beautiful ideas and interesting problems! I hope that you have met the new year at least as fun as I am. Have you had enough sleep after New Year's Eve? This year, the traditional post summarizing the past year, I sat down to write only on January 1, 2018. I hope that I will not have to sum up the whole year. This post is important to me, since it draws a line to all the work done by the Codeforces team and the entire community in 2017. Many thanks to the team: all of the achievements listed below are the result of joint efforts. We did an excellent job! The community must know its heroes. In 2017, [user:MikeMirzayanov,2018-01-02], [user:KAN,2018-01-02] (problem coordinator), ~gritukan,2018-01-02 (second problem coordinator), ~netman,2018-01-02 (ex-second problem coordinator), ~k...
I hope that you have met the new year at least as fun as I am. Have you had enough sleep after New

Full text and comments »

  • Vote: I like it
  • +1319
  • Vote: I do not like it

32.
Codeforces Round #649 (Div.2)
By mohammedehab2002, 6 years ago, In English
Codeforces Round #649 (Div.2) Hi everyone! Codeforces round #649 will take place on [contest_time:1364]. It's rated for the second division, but, as usual, first division participants can take part out of competition. The problems were created by me. I'd like to thank my forever orzable coordinator [user:antontrygubO_o,2020-06-11]; my incredible army of testers [user:dorijanlendvaj,2020-06-11], [user:300iq,2020-06-11], [user:Osama_Alkhodairy,2020-06-11], [user:AmShZ,2020-06-11], [user:Taran_1407,2020-06-11], [user:TigranMec,2020-06-11], [user:_Aaryan_,2020-06-11], [user:Mohammad_Yasser,2020-06-11], [user:zoooma13,2020-06-11], [user:lavish315,2020-06-11], [user:Utkarsh.25dec,2020-06-11], [user:NOOBxCODER,2020-06-11], and [user:Laggy,2020-06-11]; and, of course, you-know-who for the amazing codeforces and polygon platforms. This time, in an effort to kill type-races and because I'm lazy, you'll be given 5 problems and 2 hours to solve them. **UPD:** the scoring distribution will be 750-1000-1500-2000-2500...
. [user:Sr.Phoulady,2020-06-13] 5. [user:tzxydby,2020-06-13] Good luck & Have fun :D, Good luck & Have fun :D

Full text and comments »

  • Vote: I like it
  • +1165
  • Vote: I do not like it

33.
How to set a Div. 1 or a Div. 2 round on Codeforces
By KAN, 6 years ago, In English
How to set a Div. 1 or a Div. 2 round on Codeforces As you probably know, most of the rounds on Codeforces are created by active community members. We are very grateful to our talented authors from all around the world for bringing their ideas to tens of thousands of competitors, providing fun and learning experience for contestants of every expertise, from beginners to the world's top programmers. This post will cover the steps you need to take propose a round and become a problem writer on Codeforces. ## Who can be a problem author Best problems usually come from the most experienced participants. We have limited resources for rounds reviewing, so to make the process flawless for writers, starting January 1st, 2021, the following requirements for problem authors will be applied: - rating: 2100 or above, or - was a writer in the past. The restrictions may be updated in the future, the post will be updated accordingly. If your round is already in the review status, don't worry, it will be reviewed regardless of the current...
of thousands of competitors, providing fun and learning experience for contestants of every

Full text and comments »

  • Vote: I like it
  • +932
  • Vote: I do not like it

34.
April Fools Day Contest 2026
By AlperenT, 5 months ago, In English
April Fools Day Contest 2026 Hello, Codefoolers! We, [user:AlperenT,2026-03-29], [user:Ari,2026-03-29], [user:ToxicPie9,2026-03-29], [user:flamestorm,2026-03-29], [user:prvocislo,2026-03-29], [user:temporary1,2026-03-29], and [user:willy108,2026-03-29] would like to invite everyone on Codeforces to [contest:2214]! The 14th April Fools Day Contest will take place on [contest_time:2214]. This is a joke competition in which solving the problem is often easier than figuring out what the actual task is. In this round, you will be given $n$ problems where $n$ is the number of different AI models I used today and **2** hours to solve them. The contest will use extended ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them). You can submit solutions in any language allowed by Codeforces, unless the problem says otherwise. There will be at least one non-interactive problem. In case you do not care about those problems, [here](https://codeforces.me/blog/e...
Good luck, and **have fun**!

Full text and comments »

  • Vote: I like it
  • +809
  • Vote: I do not like it

35.
PinkieRabbit Cheated in Div. 1 Contest on Apr 27
By PinkieRabbit_buster, 2 years ago, In English
PinkieRabbit Cheated in Div. 1 Contest on Apr 27 I am writing to report an incident of cheating by PinkieRabbit during the recent contest 1965 on Codeforces. **PinkieRabbit asked help about problem D from others during the contest,** which is definitely against the contest rules. I have attached the evidence of the cheating behavior in the appendix, please read it. This evidence clearly shows the communications PinkieRabbit had with another person during the contest. It is a contest recording video published after contest by himself. As a former fan of PinkieRabbit, after seeing this video, I was shocked by how dishonest PinkieRabbit was. I believe such actions undermine the integrity of the competition and the platform as a whole. [user:win114514,2024-05-05] cheated by grouping up in contest 1905, finally punished by skipping. Therefore, I respectfully request that Codeforces take appropriate action against PinkieRabbit to maintain the fairness of the contests on Codeforces. He only cheated in one problem this round, so I sugg...
- Only in Chinese slang did “you're my dad” use to express thank and generally forfun.

Full text and comments »

  • Vote: I like it
  • +1076
  • Vote: I do not like it

36.
April Fools Day Contest 2024
By AlperenT, 2 years ago, In English
April Fools Day Contest 2024 Hello, <s>April Fools lovers</s> Codeforces! We, [user:AlperenT,2024-03-26], [user:flamestorm,2024-03-26], [user:toxicpie9,2024-03-26], and [user:willy108,2024-03-26], would like to invite everyone on Codeforces to [contest:1952]! The 12th April Fools Day Contest will take place on [contest_time:1952]. This is a joke competition in which solving the problem is often easier than figuring out what the actual task is. In this round, you will be given $n$ cool bugaboos where $-1 \le n \le \textbf{[REDACTED]}$ and **2** hours to solve them. The contest will use extended ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them). You can submit solutions in any language allowed by Codeforces, unless the problem says otherwise. Please note that the round is **unrated** and that the penalty for a **wrong submission** is **10** minutes. To get an idea of what the contest will look like, you can check out the contests of the pas...
Good luck, and **have fun**!

Full text and comments »

  • Vote: I like it
  • +822
  • Vote: I do not like it

37.
Don't use rand(): a guide to random number generators in C++
By neal, 8 years ago, In English
Don't use rand(): a guide to random number generators in C++ Don't use `rand()`. Why? Let's jump right into some code. What value will the following code print, approximately? ~~~~~ #include <cstdlib> #include <iostream> using namespace std; const int ITERATIONS = 1e7; int main() { double sum = 0; for (int i = 0; i < ITERATIONS; i++) sum += rand() % 1000000; cout << "Average value: " << sum / ITERATIONS << '\n'; } ~~~~~ Should be about 500,000, right? Turns out it depends on the compiler, and on Codeforces it prints 16382, which isn't even close. [Try it out yourself](http://codeforces.me/contest/1025/customtest). ### What's happening here? If you look up [C++ documentation on `rand()`](https://en.cppreference.com/w/cpp/numeric/random/rand), you'll see that it returns "a pseudo-random integral value between `0` and `RAND_MAX`." [Click again on `RAND_MAX`](https://en.cppreference.com/w/cpp/numeric/random/RAND_MAX) and you'll see that "This value is implementation dependent. It's guaranteed that th...
9999, since 32767 is not a perfect multiple of 10000. There are many other fun distributions as well

Full text and comments »

  • Vote: I like it
  • +891
  • Vote: I do not like it

38.
Codeforces Round #932 (Div. 2)
By artew, 3 years ago, translation, In English
Codeforces Round #932 (Div. 2) <img alt=" " src="https://i.imgur.com/EFlomVE.png" style="float: right;max-width: 100.0%;max-height: 100.0%;width:30%;height:30%"> <h2>Hello, Codeforces! &#128519;</h2> ------------------ We are glad to invite you to participate in [contest:1935], which will take place at [contest_time:1935] &#128293; &#128561; &#129321; The round has been fully prepared by students of the School CPM &#128147; (School of the Pedagogical Skills Center): [user:IzhtskiyTimofey,2024-02-25], [user:AndreyPavlov,2024-02-25], and myself. The theme of all the problems will be our beloved school &#128520; This round will be **rated** for participants with a rating below **2100** &#128522; Participants with a higher rating can take part out of competition &#128523; We would like to thank &#128149;: - Our wonderful coordinator [user:Artyom123,2024-02-25] for helping prepare the problems and valuable advice! &#128525; - CPM students [user:azureglow,2024-02-25] and [user:max0000561,2024-02-25] ...
We apologize for the disbalance in our problemset. However, we hope these problemfun and

Full text and comments »

  • Vote: I like it
  • +911
  • Vote: I do not like it

39.
touristreams are back! 006: SNSS 2020 R1, and more
By tourist, 6 years ago, In English
touristreams are back! 006: SNSS 2020 R1, and more It's this time of the year again! Tune in at [twitch.tv/the__tourist](https://twitch.tv/the__tourist) at around [21:45 MSK, 21 Aug 2020](https://www.timeanddate.com/worldclock/fixedtime.html?msg=touristream+006&iso=20200821T2145&p1=3396) to watch me solving [SnarkNews Summer Series 2020 Round 1](https://contest.yandex.com/snss2020/contest/19320/enter) live! First I will do the round competitively without much interaction, and I'll be up for discussing the problems on stream afterwards. SnarkNews Winter/Summer Series (SNWS/SNSS) is organized by [user:snarknews,2020-08-19] yearly and consists of 5 rounds. Each round is a virtual 6-problem 80-minute contest open for 10 days. The series is open to all, but problem statements are in Russian only. Unlike last series, I'll be reading problem statements automatically translated to English on stream. To make the stream more fun and for easier understanding of what will be going on, you're welcome to do the round yourself beforehand! If...
problem statements automatically translated to English on stream. To make the stream morefun and for, To make the stream more fun and for easier understanding of what will be going on, you're welcome

Full text and comments »

  • Vote: I like it
  • +747
  • Vote: I do not like it

40.
Codeforces Round #670 (Div. 2)
By feecIe6418, history, 6 years ago, In English
Codeforces Round #670 (Div. 2) Hello Codeforces! [user:gyh20,2020-09-10] and I are glad to invite you to [contest:1406] which will start on [contest_time:1406]. **Note the unusual start time of the round.** The contest will last for **two hours**, and you will have **five tasks** to solve. The tasks are prepared by me and [user:gyh20,2020-09-10]. This round is rated for participants whose **rating is not higher than 2099**. You can see that my current rating is exactly **2099** :) There might be an interactive problem. You can learn about them [here](https://codeforces.ml/blog/entry/45307). We would like to thank: - [user:isaf27,2020-09-10] for coordinating and helping us with the problems. - [user:namanbansal013,2020-09-10], [user:postscript,2020-09-10], [user:morzer,2020-09-10], [user:Osama_Alkhodairy,2020-09-10], [user:csani,2020-09-10], [user:growup974,2020-09-10], [user:physics0523,2020-09-10], [user:bizhouziwei20,2020-09-10] for testing the problems and providing useful feedback. Special thank...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +772
  • Vote: I do not like it

41.
About Problemsetting (for AtCoder and Codeforces)
By dario2994, 6 years ago, In English
About Problemsetting (for AtCoder and Codeforces) Since the amount of information available about the preparation of a competitive programming contest for AtCoder/Codeforces is very little, I decided to collect here what was my experience. I will try to both describe my experiences and give some general advice to wannabe problemsetters. I hope that this will be useful to future problemsetters who are "out of the loop". Moreover, participants might be curious to know what happens behind the scenes (and maybe the platforms may consider this as a form of constructive feedback). *Acronyms*: - AGC = Atcoder Grand Contest - GR = Codeforces Global Round ### Why I know something about problemsetting? I am in the competitive programming world since ~8 years: I have participated in IOI/ICPC/GCJ and a number of contests on AtCoder/Codeforces (and lately Codechef). I am not a top participant but, being in this world for so long, I know, more or less, all the standard tricks. Recently, I was the author of the *flagship conte...
that one of the problems was known (AGC44 D). 3. I had fun interacting with [user:antontrygubO_o,2020

Full text and comments »

  • Vote: I like it
  • +936
  • Vote: I do not like it

42.
Wunder Fund Round 2016
By Lewin, 11 years ago, In English
Wunder Fund Round 2016 Hello Codeforces! I invite all of you to participate in a **special** Codeforces round. It will take place on [29 Jan, 17:05 UTC](http://www.timeanddate.com/worldclock/fixedtime.html?day=29&month=1&year=2016&hour=20&min=5&sec=0&p1=166). It will not be a usual round. Thanks to Wunder Fund, the best participants will win prizes and souvenirs. Here are some words from <a href="http://wunderfund.io/">Wunder Fund</a>: <img src="http://assets.codeforces.com/images/optimization.jpg" style="float:right; margin: 0 1em;"/> > Our company is situated in the center of Moscow. We are engaged in high-frequency trading &mdash; developing high-performance systems and algorithms for automated trading in financial markets. In this area algorithms and data structures (that you love to invent and implement) are vital. Our systems should process transactions in milliseconds! High-frequency trading is a continuous competition of the best programmers and mathematicians around the world. By joining us...
I hope to see you all at the round. Good luck and have fun! :)

Full text and comments »

  • Vote: I like it
  • +707
  • Vote: I do not like it

43.
"Algorithms in Depth" Stream Series: Kicking Off With FFT
By peltorator, 15 months ago, In English
"Algorithms in Depth" Stream Series: Kicking Off With FFT Hi Codeforces! I’ve long believed that it's _really_ worth revisiting the same competitive programming topics multiple times. The first time, you’re just trying to survive and maybe grasp the basics. The second time, you’ve solved some problems, you know where you got confused, and you're ready to absorb more. By the third time, you’ve seen and solved enough to start appreciating the subtleties — the tricks, advanced applications, deeper meaning. But most lectures I’ve seen are designed as a one-size-fits-all — trying to cover everything from scratch _and_ dive into the advanced stuff in one go. That’s rarely optimal. Take binary search. I once talked about it for six hours straight. A beginner at that lecture would’ve probably quit CP immediately. And that’s ok. Beginners don’t need all that. But the truth is, there _is_ that much depth to explore even in seemingly simple topics like binary search — once you're ready. Yet many people only see the beginner version once and mo...
- **Advanced**: deep understanding, fun tricks, and higher-level abstractions.

Full text and comments »

  • Vote: I like it
  • +631
  • Vote: I do not like it

44.
Codeforces Round #485 (div.1+div.2)
By Um_nik, history, 8 years ago, In English
Codeforces Round #485 (div.1+div.2) Hello! I'm glad to invite you all to Round 485 which will take place on [Tuesday, May 29 at 18:35 UTC+3](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Codeforces+Round+%23485&iso=20180529T1835&p1=166&ah=2). There will be 6 problems in each division, 3 of them are shared between divisions. 2 of div.2 problems created by [user:KAN,2018-05-28], 7 others created by me. The contest duration is 2 hours. My problems were originally used in HSE Championship. I would like to thank [user:Merkurev,2018-05-28] and [user:GlebsHP,2018-05-28] with whom I discussed the problems, [user:I_love_Tanya_Romanova,2018-05-28] for testing, [user:KAN,2018-05-28] for round coordination and Codeforces and Polygon team for these beautiful platforms. I would also like to thank HSE for organizing the event. Oh, and [user:kb.,2018-05-28] for writing great legend for one of the problems (he will be surprised). For those who for some reason like to know score distribution in advance: div.2: 5...
Good fun, have problems, read all the luck. As usual.

Full text and comments »

  • Vote: I like it
  • +656
  • Vote: I do not like it

45.
Codeforces Round #796
By huangzirui, history, 4 years ago, In English
Codeforces Round #796 Hi Codeforces! Happy Dragon Boat Festival! We are glad to invite you to our first Codeforces Round [contest:1687] and [contest:1688] which will be held on [contest_time:1687]. This round will be rated for participants of both divisions. Participants in each division will be offered 6 problems and 2 hours to solve them. The two divisions will share 3 problems. In this round, as the best friend of the characters in Touhou Project, you are going to help them solve the problems they meet. The problems are prepared by [user:xiaoziyao,2022-05-30], [user:Yakumo_Ran,2022-05-30], [user:SSerxhs,2022-05-30], [user:Cocoly1990,2022-05-30], [user:LilyWhite,2022-05-30], [user:Elegia,2022-05-30] and me. We hope you will enjoy this round. Great thanks to: - [user:74TrAkToR,2022-05-30] for good coordination of this round and translating all statements to Russian, - [user:Yakumo_Ran,2022-05-30] for providing most tasks, - [user:SSerxhs,2022-05-30] for preparing most tasks, - [user:L...
Good luck & Have fun!

Full text and comments »

  • Vote: I like it
  • +746
  • Vote: I do not like it

46.
April Fools Day Contest 2025
By AlperenT, 17 months ago, In English
April Fools Day Contest 2025 Hello, Codefoolers! We, [user:AlperenT,2025-03-28], [user:flamestorm,2025-03-28], [user:prvocislo,2025-03-29], [user:temporary1,2025-03-28], [user:Toxicpie9,2025-03-28], and [user:-1e11,2025-03-28], would like to invite everyone on Codeforces to [contest:2095]! The 13th April Fools Day Contest will take place on [contest_time:2095]. This is a joke competition in which solving the problem is often easier than figuring out what the actual task is. In this round, you will be given $n$ problems where $\sum\limits_{x=1}^{\infty} \frac{1}{x^n}$ converges and **2** hours to solve them. The contest will use extended ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them). You can submit solutions in any language allowed by Codeforces, unless the problem says otherwise. Please note that the round is **unrated** and that the penalty for a **wrong submission** is **10** minutes. To get an idea of what the contest will look lik...
sending funny responses like we did in the last two years. It is definitely not the mostfun part of, years. It is definitely not the most fun part of April Fools. Lastly, we have a [video editorial, Good luck, and **have fun**!

Full text and comments »

  • Vote: I like it
  • +692
  • Vote: I do not like it

47.
Codeforces Round #723 (Rated for Div 2)
By errorgorn, history, 5 years ago, In English
Codeforces Round #723 (Rated for Div 2) Hello again Codeforces! [user:Errorgorn,2021-05-25], [user:Oolimry,2021-05-25] and [user:ILoveIOI,2021-05-25] are glad to invite you to participate in [contest:1526] which will be held at [contest_time:1526]. The round will be **rated for the participants with a rating lower than 2100**. Participants from the first division are also welcomed to take part in the competition but it will be unrated for them. You will be given **2 hours and 30 minutes** to solve **6 questions**. One of the puzzles is interactive, please read [the guide of interactive](https://codeforces.me/blog/entry/45307) [problems](https://en.wikipedia.org/wiki/Binary_search_algorithm) before the contest. We would like to thank: - Our lord and saviour [user:AntontrygubO_o,2021-05-25] for amazing coordination and rejecting our poopoo tasks - [user:dantoh000,2021-05-25] and [user:tqbfjotld,2021-05-25] for roasting our enigmas and testing them before they were prepared - our many testers [user:balbit,2021-05...
We hope you find the bugaboos interesting and fun! Wish you high rating!

Full text and comments »

  • Vote: I like it
  • +923
  • Vote: I do not like it

48.
Codeforces Round 1024 (Div. 1, Div. 2)
By Shoo, 16 months ago, In English
Codeforces Round 1024 (Div. 1, Div. 2) Hello, Codeforces! [user:eren__,2025-05-05], [user:sweetweasel,2025-05-05], and I are glad to invite you to [contest:2101] and [contest:2102]. Both rounds take place at [contest_time:2101], and have a duration of **2 hours** and **30 minutes**. The Division 1 contest is made up of $6$ problems, and the Division 2 contest is also made up of $6$! We would like to thank: - [user:maomao90,2025-05-05] for his wonderful coordination and *huge* help in preparing the round. - [user:Alexdat2000,2025-05-08] for the Russian translations. - Our testers: [user:mmdrzada,2025-05-05], [user:N_z__,2025-05-05], [user:Hamed_Ghaffari,2025-05-05], [user:Shahrad_Mirzaei,2025-05-05], [user:RSAMSD,2025-05-05], [user:-this-is-obd-,2025-05-05], [user:AmShZ,2025-05-05], [user:AlefHeKaaf,2025-05-05], [user:beny_kh,2025-05-05], [user:Nariman_MT,2025-05-05], [user:sohsoh,2025-05-05], [user:Shayan86,2025-05-05], [user:Nimazare,2025-05-05], [user:Amoo_Safar,2025-05-05], [user:_R00T,2025-05-05], [user:Um...
like the problems. Don't forget to have fun!, ) contest on Codeforces, so we really hope you will like the problems. Don't forget to havefun, fun round!

Full text and comments »

  • Vote: I like it
  • +794
  • Vote: I do not like it

49.
Codeforces Round #270
By cgy4ever, 12 years ago, In English
Codeforces Round #270 Do you want to win a T-shirt? Do you want to learn how to design tasks for programming contest? Do you want to solve 7 tasks in 2.5 hours? So Codeforces Round #270 is right for you. It was designed by me in California, Assembled in polygon (so Thank you [user:MikeMirzayanov,2014-09-26] for the system and [user:Gerald,2014-09-26] for organize and testing), will start on [regular time this Sunday](http://www.timeanddate.com/worldclock/fixedtime.html?day=28&month=9&year=2014&hour=19&min=30&sec=0&p1=166), don't miss it! The organizers of **<a href="/blog/entry/13929">Marathon24</a>** decided to present gifts to the best finishers of the round! Best 25 participants will get Marathon24 tshirts! Thanks! <center> <img src="http://www.elmostshirts.com/images/tshirts.jpg"/> <br><small>It is just an image to attract your attention. Real tshirts will be designed specially for Marathon24!</small> </center> There are some articles introduced how to become a problem setter, like [Pro...
Good luck and have fun!

Full text and comments »

Announcement of Codeforces Round 270
  • Vote: I like it
  • +794
  • Vote: I do not like it

50.
Codeforces Round #631 (Div. 1 and Div. 2) — Thanks, Denis aramis Shitov!
By dreamoon_love_AA, history, 6 years ago, In English
Codeforces Round #631 (Div. 1 and Div. 2) — Thanks, Denis aramis Shitov! Hello, everyone! [Codeforces Round #631](https://codeforces.me/contests/1329,1330) will be held at [contest_time:1329]. The problems are almost from me([user:dreamoon_love_AA,2020-04-01]), except one problem of which the idea is from [user:drazil,2020-04-01] and developed by me. Also we want to thank [user:300iq,2020-04-01] for helping me prepare the round, [user:isaf27,2020-04-01], [user:tmt514,2020-04-01], [user:rowdark,2020-04-01], [user:yp155136,2020-04-01], [user:wangyenjen,2020-04-01], [user:n_dao107,2020-04-01] and [user:zj713300,2020-04-01] for testing this round, and MikeMirzayanov for Codeforces and Polygon. This is my third time organizing a problemset for a Codeforces round (my previous rounds: [Codeforces Round #292](https://codeforces.me/contests/515,516), [Codeforces Round #320](https://codeforces.me/contests/578,579)). Good luck and have fun! **UPD**: Below is a message for you from [user:MikeMirzayanov,2020-04-02]: _About two weeks ago, we completed ...
Good luck and have fun!

Full text and comments »

Tags 631
  • Vote: I like it
  • +656
  • Vote: I do not like it

51.
Codeforces Round #641
By BlueSmoke, 6 years ago, In English
Codeforces Round #641 Hello, Codeforces! We are excited to invite you to [contest:1349] and [contest:1350]. This round will take place on [contest_time:1349]. In both divisions, you will have **2.5 hours** to solve **6 problems**. **Please notice the unusual time.** Problems of this round were prepared by [user:Fulisike,2020-05-04], [user:A.K.E.E.,2020-05-04], [user:mydiplomacy,2020-05-04] and me [user:ProgSlacking,2020-05-04]. We would like to express our sincere gratitude to: - [user:300iq,2020-05-04], for responsible and interesting coordination; - [user:WZYYN,2020-05-04], [user:Elegia,2020-05-04], [user:skip2004,2020-05-11], [user:vintage_Vlad_Makeev,2020-05-11], [user:fpdqwq,2020-05-04], [user:wangziji,2020-05-04], [user:Suika_predator,2020-05-04], [user:wrg0ababd,2020-05-04], [user:AcF-_-FcA,2020-05-04], [user:Kirill_from_Kazan,2020-05-04], [user:dysyn1314,2020-05-04], [user:xiaolou0411,2020-05-04], [user:LiM_256,2020-05-04], [user:HazyKnight,2020-05-04], [user:Sad_reacts_only,2020-05-0...
of you good luck and have fun! Since the round **is rated**, we also wish you guys have huge

Full text and comments »

  • Vote: I like it
  • +940
  • Vote: I do not like it

52.
Codeforces Round #738 (Div. 2)
By Bazoka13, history, 5 years ago, In English
Codeforces Round #738 (Div. 2) Hi Codeforces! We are glad to invite you to our first Codeforces Round [contest:1559] which will be held on [contest_time:1559]. This round will be **rated for participants with rating less than 2100**. We will be glad to see participants from the first division to join out of competition as well! In this round, as the best friend of Mocha's, you are going to help her to solve the problems she meets. The problems are prepared by [user:2sozx,2021-08-12], [user:JJLeo,2021-08-12], [user:Serval,2021-08-12], [user:CalvinJin,2021-08-12] and me. We hope you will enjoy the round. :P We would like to thank: - [user:1-gon,2021-08-12] for awesome coordination of this round and helping us improve our problems. - [user:Toxel,2021-08-12] for excellent testing and discussion of this round. - [user:cppascalinux,2021-08-12], [user:PurpleCrayon,2021-08-12], [user:ijxjdjd,2021-08-12], [user:m371,2021-08-12], [user:qxforever,2021-08-12], [user:fixed_lxy,2021-08-12], [user:HKvv,2021...
We recommend you to read the statements of all problems. Good luck & Have fun! :D

Full text and comments »

  • Vote: I like it
  • +796
  • Vote: I do not like it

53.
On problemsetting 2
By antontrygubO_o, history, 7 years ago, In English
On problemsetting 2 [Previous part](https://codeforces.me/blog/entry/70178) Hi there again! Previous part with opinions of some amazing problemsetters turned out to be interesting for you, so I decided to gather some more opinions :D. I really hope that this post will help someone in their problemsetting future! #### When and how did you start problemsetting? [user:300iq,2020-01-11]: April, 2017 [user:maroonrk,2020-01-11]: In 2015 Summer, I hold the first contest with friends at high school club. It was a local Japanese contest. [user:Radewoosh,2020-01-11]: In high school, so probably for 5 years. I was creating problems for other people from my school as my teacher told me that it's a completely different point of view. [user:voidmax,2020-01-11]: It was 3 years ago. I was on plane and I didn't have a clue what to do in my free time. Then I realized that I can try myself in problemsetting. Later I created first and one of my favorite problem ([problem:963B]). I was full of inspiration a...
writing rounds for fun, right? And where is fun when you immediately starting to write solution

Full text and comments »

  • Vote: I like it
  • +631
  • Vote: I do not like it

54.
Introducing CF Stonks — A Virtual Stock Market Based on Your CodeForces Rating!
By codetiger927, history, 5 years ago, In English
Introducing CF Stonks — A Virtual Stock Market Based on Your CodeForces Rating! **2/11/2023 Update**: There had been a month-long hiatus due to the CF name change magic (and my own laziness oops), but everything has been fixed now :D! However, I know a lot of people have gone inactive due to the month-long market closure, so I am hoping to **relaunch StonksCF** in the near future with some new mechanisms (dividends, automatic algorithm trading, etc.). Let me know if you have any ideas! In the meantime, feel free to continue exploiting the way-over-inflated economy and embrace your inner capitalism >:D **Final Update**: We now have our own **DISCORD SERVER**. Join us for the latest information and engage with the community at [https://discord.gg/AeH2GTwkF5](https://discord.gg/AeH2GTwkF5) All the announcements will be there instead of on this page Greetings Fellow CodeForces users! I am proud to introduce my latest project, [CF Stonks](https://codetiger.me/project/StonksCF) (aka StonksCF), which is a virtual stock market based on your CodeForces rating. ...
the second! Have fun trading everyone, Good luck and have fun playing :D

Full text and comments »

  • Vote: I like it
  • +711
  • Vote: I do not like it

55.
Chinese Postman Problem: How I Ran a 180 km Ultramarathon Through Every Street in My City
By brunomont, 3 months ago, In English
Chinese Postman Problem: How I Ran a 180 km Ultramarathon Through Every Street in My City Hello, Codeforces! A couple of years ago, a friend of mine told me that two cyclists had passed through every single street in the center region of the city I live in (Belo Horizonte, southeastern Brazil), on the [third try](https://www.strava.com/activities/1030665876/overview). <spoiler summary="First try"> After ~160 km, they had not completed 1/3 of the goal. [Strava link](https://www.strava.com/activities/976021527). <img src="/predownloaded/8a/53/8a53829f7d78e88808a3ff751b64406ec2fc0efd.png" style="width: 600.0px;max-width: 100.0%;max-height: 100.0%;"> </spoiler> <spoiler summary="Second try"> They were better prepared, but one of the guys was run over by a car (no big injuries). [Strava link](https://www.strava.com/activities/999450285). <img src="/predownloaded/85/8f/858fdcdcfda93cd1d9c7c59db7dbfad9e63d6ea2.png" style="width: 600.0px;max-width: 100.0%;max-height: 100.0%;"> </spoiler> <center> <img src="/predownloaded/8d/5c/8d5cfb677a361654105e49f36f214c35...
Anyways, this was very, very fun. I want to thank all my friends that participated in this

Full text and comments »

  • Vote: I like it
  • +802
  • Vote: I do not like it

56.
Codeforces Round #789
By tokitsukaze, 4 years ago, In English
Codeforces Round #789 Hello, Codeforces! ฅ(*`ω´*)ฅ We are glad to invite you to take part in [contest:1677] and [contest:1678], which will be held on [contest_time:1677]. The round will be **rated** for all participants from both divisions. Participants in each division will be offered **6** problems and **2** hours to solve them. Both divisions will share 4 problems. The problems were written and prepared by [user:funer,2022-05-05], [user:dark_light,2022-05-05], [user:FreshP_0325,2022-05-05], [user:Frank_DD,2022-05-05], [user:qsmcgogo,2022-05-05], [user:winterzz1,2022-05-05], [user:Heltion,2022-05-05], [user:TomiokapEace,2022-05-05] and me. Thank to: - [user:74TrAkToR,2022-05-05] for excellent coordination of this round! And translating the statements to Russian. - [user:KAN,2022-05-08] for helping us to review and fix some statements. - [user:TomiokapEace,2022-05-05] for helping us to translate **all** the statements and tutorials to English. - [user:Heltion,2022-05-05] for giving...
Finally, I hope you like the problems in this round, good luck and have fun !(≧ω≦)/

Full text and comments »

  • Vote: I like it
  • +765
  • Vote: I do not like it

57.
Codeforces Round #665 (Div. 2)
By 055D, 6 years ago, In English
Codeforces Round #665 (Div. 2) Hello Codeforces! I'm glad to invite you to participate in [contest:1401] taking place on [contest_time:1401]. The round is **rated for users whose rating is lower than 2100**. All problems were mainly created and prepared by me, and I'd also like to thank: - [user:adedalic,2020-08-20] for coordinating and reviewing the round, - [user:AmShz,2020-08-20], [user:growup974,2020-08-20], [user:dorijanlendvaj,2020-08-20], [user:Osama_Alkhodairy,2020-08-20], [user:Mohamed.Sobhy,2020-08-20], [user:pikmike,2020-08-20], [user:kdjonty31,2020-08-20], [user:csani,2020-08-20], [user:BledDest,2020-08-20], [user:saurabhshadow,2020-08-20], [user:postscript,2020-08-20], [user:errorgorn,2020-08-20] for testing the problems and giving feedback, - [user:MikeMirzayanov,2020-08-20] for Codeforces and Polygon platforms, - All users for participating in the contest! You will be given **6 problems** and **2 hours** to solve them. The score distribution will be announced closer to the start ...
Good luck, and have fun!

Full text and comments »

  • Vote: I like it
  • +717
  • Vote: I do not like it

58.
Codeforces Round #630 (Div. 2)
By triple__a, history, 6 years ago, In English
Codeforces Round #630 (Div. 2) Hello Codeforces! I am glad to invite you to my first official round [contest:1332], which will take place on [contest_time:1332] **(please note for the unusual starting time)** and will be rated for **all Division 2 participants**. You will be given **7 tasks** and **150 minutes** to solve them. All tasks in this round were prepared by me. Hope that you will enjoy those tasks! I would like to thank: - [user:pikmike,2020-03-29] for great coordination of this round, and the idea of solution of one task! - [user:Nanako,2020-03-29], [user:nezzar,2020-03-29] for useful discussion and testing this round! - [user:antontrygubO_o,2020-03-29], [user:McDic,2020-03-29], [user:vovuh,2020-03-29], [user:Flowerandyouth,2020-03-29], [user:socho,2020-03-29], [user:Oak_limy,2020-03-29], [user:Amori,2020-03-29], [user:Stresshoover,2020-03-29], [user:I1I1I11I1I1,2020-03-29], [user:defolaut,2020-03-29], [user:hx073269,2020-03-29] and [user:Pavlova,2020-03-29] for testing this round and...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +713
  • Vote: I do not like it

59.
Codeforces Round #659
By Devil, 6 years ago, In English
Codeforces Round #659 Hello, Codeforces! I'm very glad to invite you to the first **Cuban round** [contest:1383] and [contest:1384] which will take place on [contest_time:1383]. All problems in this round were created and prepared by [user:marX,2020-07-21], [user:gilcu3,2020-07-21], [user:dcordb,2020-07-21], [user:jcg,2020-07-21] and me. We tried to make them interesting and diverse and hope that you will enjoy them! You will be given **2 hours** to solve **6 problems** in both divisions, and we **highly** encourage you to read all of them :) We would like to thank: - [user:antontrygubO_o,2020-07-21] for amazing coordination of this round. - [user:Um_nik,2020-07-21], [user:gamegame,2020-07-21], [user:ffao,2020-07-21], [user:eatmore,2020-07-21], [user:isaf27,2020-07-21], [user:balbit,2020-07-21], [user:Tlatoani,2020-07-21], [user:Prabowo,2020-07-21], [user:Kuroni,2020-07-21], [user:hugopm,2020-07-21], [user:MagentaCobra,2020-07-21], [user:qlf9,2020-07-21], [user:faremy,2020-07-21], [use...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +732
  • Vote: I do not like it

60.
Refact.ai Match 1 (Codeforces Round 985, Div. 1 + Div. 2)
By sszcdjr, history, 23 months ago, In English
Refact.ai Match 1 (Codeforces Round 985, Div. 1 + Div. 2) Hello, Codeforces! We (KDOI Team) are glad to invite you to take part in [contest:2029], which is the 8th CP contest held by us! You can view the previous rounds by us [here](/blog/entry/135847). - Number of problems: $9$ ($0$ interactive); - Start time: [contest_time:2029]; - Contest duration: $180$ minutes; - Score distribution: $750-1250-1750-2250-2500-3000-3500-5000-5500$. The problems were authored and prepared by [user:Error_Yuan,2024-11-05], [user:wyrqwq,2024-11-05], [user:Otomachi_Una,2024-11-05] and me [user:sszcdjr,2024-11-05]. --- <img src="/predownloaded/73/e1/73e1593107761ee6b925164110aa7307488b2215.png" style="float:right; margin: 0 0 2em 2em; width:300px;"/> A few words from our sponsor: We’re [Refact.ai](https://refact.ai/?utm_source=codeforces&utm_medium=post&utm_campaign=round_09112024&utm_content=cf_short_09112024), an open-source AI Coding Assistant, and on November 9th, we’ll be hosting our first round on Codeforces! Winners will receive ...
Good Luck & Have Fun!

Full text and comments »

  • Vote: I like it
  • +655
  • Vote: I do not like it

61.
Codeforces Round 1000 (Div. 2)
By chromate00, 20 months ago, In English
Codeforces Round 1000 (Div. 2) Hello Codeforces, and the legends of across $999$ and more rounds! ------------------------------------------------------------------ --- [user:wuhudsm,2024-12-25], [user:Yugandhar_Master,2025-01-15], and I are *beyond excited* to invite you to [contest:2063] at [contest_time:2063]. <b style="color:red;">Please note the unusual time of the round ($\color{red}{2.5}$ hours before the usual time)!</b> The contest contains $6$ carefully crafted tasks, one of them divided into two subtasks, to be solved in $2$ hours. You will solve tasks themed around Little John and his shenanigans aimed towards getting his own dream home (featuring, probably, galvanized square steel). This round could not exist without the thankful help of these so many people: - ~FairyWinx,2025-01-15 for <strike>rejecting more tasks than are used in the final problemset,</strike> coordinating the round and translating the problems; - ~rewhile,2025-01-15 for some very important "technical assistance"; - ...
Anyways, that's all for the announcement; **Good luck, and have fun!**

Full text and comments »

  • Vote: I like it
  • +679
  • Vote: I do not like it

62.
Codeforces Round #816 (Div. 2)
By ilyakrasnovv, 4 years ago, translation, In English
Codeforces Round #816 (Div. 2) Thanks a lot! ================== for Your participation Hello, Codeforces! We are glad to invite everyone to participate in [contest:1715], which will be held on [contest_time:1715]. The round will be rated only for the second division. You will have **6 tasks** and **2 hours** to solve them. _We recommend you read all the problems_. Round is completely set by winter SIS (Summer Informatics School) students. During the camp we did our best to prepare interesting and creative problems. You can check previous rounds prepared by SIS students: [contest:1720], [Codeforces Round #694](https://codeforces.me/contests/1471,1470), [Codeforces Round #612](https://codeforces.me/contests/1286,1287), [Codeforces Round #530](https://codeforces.me/contests/1098,1099) We are very thankful to - task authors and developers: Vasilyev [user:Allvik06,2022-08-17] Alexey, Denis [user:Kapt,2022-08-17] Mustafin, Ivan [user:__silaedr__,2022-08-17] Podvorniy, Ilya [user:ilyakrasnovv,2022-08-1...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +703
  • Vote: I do not like it

63.
Codeforces Round #453 (Div. 1 & Div. 2)
By adamant, 9 years ago, translation, In English
Codeforces Round #453 (Div. 1 & Div. 2) Hi everyone! Missed me? I bet no! In either way, here goes another one round which I dared to spoil by my participation in problemsetting. Welcome to the world of extremely unoriginal problems, awkwardly long and boring statements and trifling jokes in anouncements. This time round was prepared by Ildar Gainullin ([user:gainullin.ildar,2017-12-18]) and me (I'm ashamed to place link of such color here, you know who). We want to thank Vladislav Isenbaev ([user:winger,2017-12-18]), Konstantin Semenov ([user:zemen,2017-12-18]), Alexey Shmelev ([user:ashmelev,2017-12-18]), Ivan Smirnov ([user:ifsmirnov,2017-12-18]) and Alex Fetisov ([user:AlexFetisov,2017-12-18]) for testing problems and help in preparation. Also special thanks goes to Nikolay Kalinin ([user:KAN,2017-12-18]) for his help as coordinator and, of course, [user:MikeMirzayanov,2017-12-18] for polygon and codeforces. We hope that you will enjoy the problems, good luck and have fun! **UPD**. Also thanks to [user:akv...
We hope that you will enjoy the problems, good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +959
  • Vote: I do not like it

64.
CF Sweatshirt signed by legends at ICPC World Finals
By SecondThread, history, 5 years ago, In English
CF Sweatshirt signed by legends at ICPC World Finals Good morning! ICPC World Finals just concluded in Moscow. I was lucky enough to be participate representing the University of Central Florida, who finished in a respectable 17th place. While there, friends, acquaintances, and CF Legends signed my Codeforces sweatshirt in their handle with their current color. The most common request of the people I asked was to show off what it ended up looking like on a blog post of Codeforces, so here that is! ![ ](https://wumbogames.github.io/cfPictures/IMG_2102.png) ![ ](https://wumbogames.github.io/cfPictures/IMG_2101.png) <spoiler summary="Famous Signings"> ![ ](https://wumbogames.github.io/cfPictures/IMG_2075.png) ![ ](https://wumbogames.github.io/cfPictures/IMG_2078.png) </spoiler> #### Signers: - [user:MikeMirzayanov,2021-10-11] the creator and maintainer of Codeforces and Polygon who deserves our eternal thanks, and [user:Una_Shem,2021-10-11] without whose work there would be no sweatshirt to sign. - [user:tourist,2021-1...
I've only seen virtually before in person. If you have any fun pictures from WF that you're itching

Full text and comments »

  • Vote: I like it
  • +772
  • Vote: I do not like it

65.
Codeforces Round #290
By cgy4ever, 12 years ago, In English
Codeforces Round #290 Fox Ciel is back! I invite you to participate in Codeforces Round #290, which will start at the [standard time on next Monday](http://www.timeanddate.com/worldclock/fixedtime.html?day=2&month=2&year=2015&hour=19&min=30&sec=0&p1=166): This is my 4th round on Codeforces, my previous rounds: [#190](http://codeforces.me/blog/entry/8163), [#228](http://codeforces.me/blog/entry/10605), [#270](http://codeforces.me/blog/entry/13997). Last Div1 Round ([#286](http://codeforces.me/blog/entry/15842)) is so hard, so after notice that, we decide to reduce the difficulty of this round. (For example, current Div1-E was used as Div1-D) I hope more people can enjoy all tasks in this round: this time no task requires advanced knowledge like linear space or Fourier Transform. The background story will be Fox Ciel's life: learning programming, play games, traveling, have dinner and so on. Like Round [#228](http://codeforces.me/blog/entry/10605), top-20 contestants that are currently at...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +636
  • Vote: I do not like it

66.
A Huge Update on The Ultimate Topic List
By YouKn0wWho, 2 years ago, In English
A Huge Update on The Ultimate Topic List Hi, around 3 years ago I compiled most of the Competitive Programming topics in one place [here](https://codeforces.me/blog/entry/95106) with relevant resources, templates, and problems. It got great responses, it now has 4000+ upvotes and the blog website has been visited 200k+ times! But it contained links to only 1-2 resources and problems per topic and it didn’t contain basic topics for beginners. Also, there was no way of tracking your progress. This time I decided to improve it, by a lot. I took this project one month ago and it took me on average 6h-10h per day for the last one month to complete this project (also I was doing a full-time job). I hope it was worth it! The new version is not just a blog, it is a full-fledged website with multiple features (I have hosted it on one of my existing websites): ![topic_list](/predownloaded/7e/20/7e2045c57574d37e170ea3eb1fdc5516ff68bc0e.png) - **Topics:** The website contains around 500 topics and tricks. Not all topics are ...
before, all I want to say is, please don't forget to enjoy the journey and have fun while riding the boat

Full text and comments »

  • Vote: I like it
  • +792
  • Vote: I do not like it

67.
Nebius Welcome Round (Div. 1 + Div. 2, rated, t-shirts!)
By GlebsHP, history, 3 years ago, In English
Nebius Welcome Round (Div. 1 + Div. 2, rated, t-shirts!) Hello, Codeforces! [user:Zlobober,2023-03-09] and I are glad to invite you to compete in Nebius Welcome Round (Div. 1 + Div. 2) that will start on [contest_time:1804]. The round will be rated for everyone and will feature 8 problems that you will have 2 hours to solve. I feel really thrilled and excited about this round as this is the first time I put so much effort in a Codeforces contest since I quit being a round coordinator in December 2016 (wow, that was so long ago)! We conduct this round to have some fun and we also hope to find some great candidates to join Nebius team. Solving 5+ problems in our round will be a good result and will count as one of the coding interviews. Apart from that top 25 contestants and 25 random contestants placed 26-200 will receive a branded Nebius t-shirt! <img style="float: right; margin: 0 1em 0.5em 1em; width: 400px;" src="/predownloaded/40/37/403770e78d9c8962d0bc0c20a9e1c45d0e3c5df9.png"> Some information about Nebius. I have join...
We conduct this round to have some fun and we also hope to find some great candidates to join

Full text and comments »

  • Vote: I like it
  • +720
  • Vote: I do not like it

68.
Pinely Round 1 (Div. 1 + Div. 2)
By pigstd, 4 years ago, In English
Pinely Round 1 (Div. 1 + Div. 2) <img align="right" alt="text" src="/predownloaded/1c/91/1c91ed031100f3338aa5f8ed58d0405adb9ff9d7.png" style="height: 500.0px;max-width: 100.0%;max-height: 100.0%;"> Hello, Codeforces! Members of team EZEC are glad to invite you to participate in **[contest:1761]**, which will start on **[contest_time:1761]**. You will be given **7** problems, **one of which has a subtask**, and **2 hours and 30 minutes** to solve them. The round will be rated for everyone. It is greatly recommended to read all the problems. There is at least one interactive problem, so please see the [guide of interactive problems](https://codeforces.me/blog/entry/45307) if you are unfamiliar with it. We would also like to thank: - Our red sun [user:orzdevinwang,2022-11-19], the youngest TOP10 coder in history, for illuminating our path. - Our great emperor [user:antontrygubO_o,2022-11-19] for cooperating and coordinating with us to make this round happen. He saved the round by contributing his problem...
Fun facts:

Full text and comments »

  • Vote: I like it
  • +590
  • Vote: I do not like it

69.
April Fools Day Contest 2020
By Nickolas, 6 years ago, translation, In English
April Fools Day Contest 2020 The contest is over; I hope you enjoyed it! The editorial is available [here](https://codeforces.me/blog/entry/75480). --- The 8th April Fools Day Contest will take place on Wednesday [April 1st](https://www.timeanddate.com/worldclock/fixedtime.html?day=1&month=4&year=2020&hour=17&min=35&sec=0&p1=166). This is a joke competition in which solving the problem is often easier than figuring out what the actual task is. In this round you'll be given several weird problems and 2 hours to solve them. The contest will use ACM ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them), and it will be unrated. You can submit solutions in any language allowed by Codeforces, unless the problem says otherwise. To get an idea of what the contest will look like, you can check out the contests of the past years: [2012](http://codeforces.me/contest/171), [2013](http://codeforces.me/contest/290), [2014](http://codeforces.me/contest/409)...
competing in this round you'll need a sense of humor compatible with mine. Good luck, and havefun!, luck, and have fun!

Full text and comments »

  • Vote: I like it
  • +1014
  • Vote: I do not like it

70.
April Fools Day Contest 2023
By flamestorm, 3 years ago, In English
April Fools Day Contest 2023 Hello, Codeforces! I, along with [user:AlperenT,2023-03-30], [user:Ari,2023-03-30], [user:BucketPotato,2023-03-30], [user:ScarletS,2023-03-30], and [user:ToxicPie9,2023-03-30], would like to invite everyone on Codeforces to the [contest:1812]! The 11th April Fools Day Contest will take place on [contest_time:1812]. This is a joke competition in which solving the problem is often easier than figuring out what the actual task is. Please note that the round is **unrated**. In this round you'll be given $n$ weird problems and 2 hours to solve them, where $7 \leq n \leq 12$. At most $\sqrt{n}$ of the problems will be [interactive](https://codeforces.me/blog/entry/45307). The contest will use ACM ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them). You can submit solutions in any language allowed by Codeforces, unless the problem says otherwise. To get an idea of what the contest will look like, you can check out the ...
Good luck, and have fun!

Full text and comments »

  • Vote: I like it
  • +576
  • Vote: I do not like it

71.
Codeforces Round 960 (Div. 2)
By wuhudsm, history, 2 years ago, In English
Codeforces Round 960 (Div. 2) Hello Codeforces! I have the pleasure of inviting you to participate in [contest:1990], which will start on [contest_time:1990]. The problems were prepared and authored by [user:wuhudsm,2024-06-26]. You will be given **6 problems** and **2 hours** to solve, one of the problems is divided into two subtasks. One of the problems may be **interactive**. So, please refer to the guide on [interactive problems](https://codeforces.me/blog/entry/45307) if you are unfamiliar with them. I would like to thank: - [user:Akulyat,2024-04-26] for coordinating the round; - [user:BurnedChicken,2024-02-26] for the only <a class="rated-user user-legendary">LGM</a> testing; - [user:physics0523,2024-02-26], [user:liympanda,2024-02-26], [user:culver0412,2024-02-26], [user:Dominater069,2024-02-26], [user:TheScrasse,2024-02-26], [user:Andreasyan,2024-02-26],[user:satyam343,2023-11-20] for <a class="rated-user user-red">GM</a> and <a class="rated-user user-red">IGM</a> testing; - [user:Er...

Full text and comments »

  • Vote: I like it
  • +575
  • Vote: I do not like it

72.
Codeforces Global Round 18
By PurpleCrayon, history, 5 years ago, In English
Codeforces Global Round 18 <img src="/predownloaded/2e/e2/2ee2f0f95f05aae6ca6f47812dae2dc2aabf277b.png" style="width:200px; float:right; margin: 0 1em 1em 1em"/> Happy Holidays! On [contest_time:1615] we will host [contest:1615]. It is the sixth round of a 2021 series of [Codeforces Global Rounds](/blog/entry/65002). The rounds are open and rated for everybody. The presents for this round: - 30 best participants get a t-shirt. - 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive. The presents for the 6-round series in 2021: - In each round top-100 participants get points according to the table. - The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest. - The best 20 participants over all series get sweatshirts and place certificates. Thanks to XTX, which in 2021 supported the global rounds initiative! The problems were written and prepared by the hard-working elves [user:1-gon,2021-12...
Good luck, have fun, and stay off the naughty list!

Full text and comments »

Announcement of Codeforces Global Round 18
  • Vote: I like it
  • +609
  • Vote: I do not like it

73.
I'm ecnerwala. Ask Me Anything!
By ecnerwala, history, 6 years ago, In English
I'm ecnerwala. Ask Me Anything! Hi everyone! [user:aop,2020-08-12] recently asked "[How is ecnerwala?](https://codeforces.me/blog/entry/81344)" I'm here to answer that question and others you may have! I'll check this regularly for the next couple of days and try to respond when I get a chance. Ask me anything! To [user:aop,2020-08-12]: I'm doing good. Quarantine is still ongoing, so I'm spending most of my time at home with my family, coding both for work and for fun. How about you? **EDIT**: There have been a lot of repeat questions, and I've tried to answer each question at least once. I've given a bunch of general advice about practicing and training, and I don't think I can say too much about how *you* specifically should practice, so I might not answer all of those questions. In general, practice things that you see in contest that are medium or hard but not impossible for you. **UPDATE**: Thank you guys for all your questions! I think I'm done answering questions for now, hope to compete with you ...
time at home with my family, coding both for work and for fun. How about you?, with my family, coding both for work and for fun. How about you? **EDIT**: There have been a lot

Full text and comments »

  • Vote: I like it
  • +777
  • Vote: I do not like it

74.
Codeforces Round #804 (Div. 2)
By cadmiumky, history, 4 years ago, In English
Codeforces Round #804 (Div. 2) Hello, Codeforces! Or, as we like to say in Romania: *Noi nu spunem asa ceva, Codeforces!* We are proud to finally invite you to participate in [Codeforces Round #804](https://codeforces.me/blog/entry/103966), which will start on [Monday, July 4th, 2022, 14:35 UTC](https://www.timeanddate.com/worldclock/fixedtime.html?day=4&month=7&year=2022&hour=17&min=35&sec=0&p1=166) You will be given **5** problems and **2** hours to solve them. We greatly recommend to read all the problems, statements are very short and straight to the point. In this round, the theme is not Independance Day related. I know, maybe we should've made the theme "Freedom", but we are not Americans and the puns within the problems were already written. Joining me on the problem setting panel are: - Setters: Gheorghies [user:Gheal,2022-06-17] Alexandru, Cozma [user:tibinyte,2022-06-17] Tiberiu-Stefan, Voicu [user:cadmiumky,2022-06-17] Mihai Valeriu - Vip-Testers: [user:Um_nik,2022-06-17], [user:a...
Good luck & have fun & the third part!

Full text and comments »

  • Vote: I like it
  • +561
  • Vote: I do not like it

75.
Good Bye 2016 sponsored by Barcelona ACM-ICPC Camp
By Errichto, 10 years ago, In English
Good Bye 2016 sponsored by Barcelona ACM-ICPC Camp Hello everybody! On December 30 at 14:05 UTC/17:05 MSK ([check your time zone here](http://timeanddate.com/worldclock/fixedtime.html?day=30&month=12&year=2016&hour=17&min=5&sec=0&p1=166)) Codeforces will host the New Year's contest Good Bye 2016. The contest is combined for both divisions, lasts 2.5 hours and contains 8 problems. Thanks to <a href="http://harbour.space/">Harbour.Space</a> and <a href="http://in.harbour.space/icpc/"> Barcelona ACM-ICPC Programming Bootcamp 2017</a> sponsoring the contest, winners can expect really cool prizes: - 5 best participants (not ACM ICPC veterans) will win free participation in Hello Barcelona programming bootcamp. - 30 best participants (not ACM ICPC veterans) will receive a 30% discount for participation in Hello Barcelona programming bootcamp. - 100 best participants will receive t-shrits by organizers and Codeforces. <center> <img src="http://codeforces.me/predownloaded/dd/0f/dd0fbc52ada73fb48011ce52adee739a248fa804.png"/> </...
Don't forget to register. I wish you great fun and no frustrating bugs.

Full text and comments »

Announcement of Good Bye 2016
  • Vote: I like it
  • +556
  • Vote: I do not like it

76.
I Reached GM after 5 years
By prvocislo, history, 4 years ago, In English
I Reached GM after 5 years Hello Codeforces! I did it! My main goal for 2022 was to reach red and I succeeded in the last contest of the year by getting +1 delta and going from cursed 2399 to 2400! I was very happy but scared to celebrate because I was worried that my rating would go down to 2399 again after the cheater removal. But now it’s 2401, so I think I’m safe now. Why am I writing this blog? I'm very excited about this achievement, it means a lot to me and I want to share my happiness with Codeforces. Also people ask me in DM quite often about how I got onto this level or who I am in general, so I think it's time to summarize it all into one blog post. Oh, wait… You don’t even know me, so why should you keep reading this blog post? Let me introduce myself a little first. I’m a high schooler from a small European country where few people do Codeforces. I love competing in OI and MO, I always did. One day, my father found the Codeforces website and suggested that I should start practicing there. At ...
5. Have fun when practicing! Don’t take CP or rating too seriously. Find a way of practicing you

Full text and comments »

  • Vote: I like it
  • +716
  • Vote: I do not like it

77.
Codeforces Round #831 (Div. 1 + Div. 2, based on COMPFEST 14 Final)
By steven.novaryo, history, 4 years ago, In English
Codeforces Round #831 (Div. 1 + Div. 2, based on COMPFEST 14 Final) <img alt="logo" src="/predownloaded/03/5f/035ff83d655937b478f5fe9f351f79ac0781f6d2.png" style="float: right;height: 100.0px;margin: 10.0px;max-width: 100.0%;max-height: 100.0%;"> Halo, **Codeforces**! &#x1f970;&#x1f970;&#x1f970;&#x1f970; COMPFEST 14 is happy to invite you to participate in [contest:1740] on [contest_time:1740]. **Note the unusual time of the round**. The round will be **rated for everyone**. You will be given **2 hours and 45 minutes** to solve **9 problems**. The problems are written by [user:NeoZap,2022-10-26], [user:Nyse,2022-10-26], [user:Pyqe,2022-10-26], and [user:steven.novaryo,2022-10-26]. Scoring distribution: **500 &mdash; 1000 &mdash; 1500 &mdash; 1750 &mdash; 2000 &mdash; 2500 &mdash; 2750 &mdash; 3000 &mdash; 3500** We would like to thank: - [user:KAN,2022-10-26] for helping to host the round; - [user:errorgorn,2022-10-26] for the based coordination and help with the problem preparation; - [user:Zappeko,2022-10-26] for helping with the ...
We hope you will enjoy and have fun in the contest. Semoga beruntung dan selamat bersenang-senang

Full text and comments »

  • Vote: I like it
  • +693
  • Vote: I do not like it

78.
Codeforces Round #902 (Div. 1, Div. 2, based on COMPFEST 15 — Final Round)
By Pyqe, 3 years ago, In English
Codeforces Round #902 (Div. 1, Div. 2, based on COMPFEST 15 — Final Round) <img alt="logo" src="/predownloaded/e3/33/e333915aebea955b43b4ad17845f6dbf58875a0c.png" style="float: right;height: 100.0px;margin: 10.0px;max-width: 100.0%;max-height: 100.0%;"> Sugeng enjing, **Codeforces**! &#x1f970;&#x1f970;&#x1f970;&#x1f970; COMPFEST 15 is happy to invite you to participate in [contest:1876] and [contest:1877] on [contest_time:1876]. Both rounds will be **rated**. You will be given **2 hours and 30 minutes** to solve **7 problems**. **Note the unusual time of the round**. ------------------ The problems are written by [user:ArvinCiu,2023-10-03], [user:Pyqe,2023-10-03], and [user:nandonathaniel,2023-10-03]. We would like to thank: - [user:KAN,2023-10-03] for helping to host the round; - [user:errorgorn,2023-10-03] and [user:ScarletS,2023-10-03] for the based coordination; - [user:gansixeneh,2023-10-03] and [user:nandonathaniel,2023-10-03] for helping with the problem preparation; - [user:ArvinCiu,2023-10-03], [user:CyberSleeper,2023-10-03], an...
We hope you will enjoy and have fun in the contest. Muga-muga beja lan isa entuk biji apik

Full text and comments »

  • Vote: I like it
  • +570
  • Vote: I do not like it

79.
ICPC North America Championship: Call for Fun Facts
By SecondThread, 3 years ago, In English
ICPC North America Championship: Call for Fun Facts Fun Facts about NAC Teams ================== Are you or someone you know attending the North America Programming Camp? If so, we'd love to get some fun facts about the teams that are here! Please submit your fun facts [in this google form](https://forms.gle/6urswk25LchFw2uR6), or send them in a direct message to me, [user:SecondThread,2023-05-27] on Codeforces! ![ ](https://github.com/WumboGames/WumboGames.github.io/blob/master/cfPictures/nac.jpg?raw=true) What kind of facts are you looking for? ------------------ We're looking for anything exciting, interesting, or varied about your team that you're willing to share. Some great examples that we've seen in the past include: - I play Smash Melee competitively in my free time - One of our team members (his_handle) is getting married within a week of finals - I'm surprisingly not actually a Computer Science major, instead I'm majoring in x and plan to use it for y. - 2/3 of our team uses the non-C++ programming langua...
ICPC North America Championship: Call for Fun Facts, Fun Facts about NAC Teams ================== Are you or someone you know attending the North, Please submit your fun facts [in this google form](https://forms.gle/6urswk25LchFw2uR6), or send

Full text and comments »

  • Vote: I like it
  • +217
  • Vote: I do not like it

80.
ICPC Dhaka: Call for Fun Facts
By SecondThread, history, 4 years ago, In English
ICPC Dhaka: Call for Fun Facts Fun Facts About World Finals Teams ================== Are you participating in ICPC World Finals in Dhaka this week? Is someone from your team competing in World Finals? Did your best friend's brother meet someone whose cousin competed in regionals against a team who qualified? If so, we'd love to get some fun facts about the world finals team from you! If you have any, please submit your fun facts [in this google form](https://forms.gle/VXfD95C4yDsoR2FPA), or send them in a private message to me, [user:SecondThread,2022-11-05], on Codeforces! ![ ](/predownloaded/b7/df/b7df472ba2dcd60580fb0b29299af6435e7fae31.jpg) #### What kind of facts are you looking for? Well variety is what makes things exciting, so we don't want to limit it too much. But for some inspiration, some good ones we've seen in the past include: - I play Smash Melee competitively in my free time - One of our team members (his_handle) is getting married within a week of finals - I'm surprisingly n...
ICPC Dhaka: Call for Fun Facts, against a team who qualified? If so, we'd love to get some fun facts about the world finals team from, Fun Facts About World Finals Teams ==================, If you have any, please submit your fun facts [in this google form](https://forms.gle

Full text and comments »

  • Vote: I like it
  • +201
  • Vote: I do not like it

81.
Codeforces Round 1005 (Div. 2)
By Intellegent, history, 19 months ago, In English
Codeforces Round 1005 (Div. 2) <center> <img src="https://i.imgur.com/McpYICK.png" style="width: 125.0px;max-width: 100.0%;max-height: 100.0%;"></center> <center> <h1> Hello Codeforces! </h1> </center> I am very excited to offer you to participate in [contest:2064], starting at [contest_time:2064]. There will be **6** very epic tasks and you will have **2 hours** to solve them. All problems were authored and prepared by me. This round will be **rated for all participants with rating below 2100**. I would like to thank the following list of orzosities for making this round possible: - [user:flamestorm,2025-02-13] for coordinating and helping with problem preparation. - My army of testers: [user:N_z__,2025-02-13], [user:triple__a,2025-02-13], [user:sammyuri,2025-02-13], [user:_istil,2025-02-13], [user:Dominater069,2025-02-13], [user:nifeshe,2025-02-13], [user:awesomeguy856,2025-02-13], [user:Error_Yuan,2025-02-13], [user:anango,2025-02-13], [user:temporary1,2025-02-13], [user:efishel,2025-02-13], [u...
**Good luck, have fun** and I hope you have non-negative rating changes!

Full text and comments »

  • Vote: I like it
  • +551
  • Vote: I do not like it

82.
Codeforces Round #691, based on ByteDance — Moscow Workshops Online Contest
By Endagorion, history, 6 years ago, In English
Codeforces Round #691, based on ByteDance — Moscow Workshops Online Contest ![ ](https://sf1-scmcdn2-tos.pstatp.com/biz_platform/fe/arch_winter_camp_pc/img/header-image-en.25fc0604.png) Hello, Codeforces community! I'm glad to invite you to Codeforces Round #691 (Div. 1) and Codeforces Round #691 (Div. 2), which will be held on [contest_time:1459]. **The round will be rated for both divisions.** The problems were taken (mostly) from the ByteDance — Moscow Workshops Online Contest, which is happening at the same time. They were prepared by me, [user:AndreySergunin,2020-12-17], and [user:amethyst0,2020-12-17]. We are very thankful to the testers: [user:low_,2020-12-18], [user:__rkm__,2020-12-18], [user:ecnerwala,2020-12-18], [user:Tima,2020-12-18], [user:IITianUG,2020-12-18], [user:thenymphsofdelphi,2020-12-18], [user:mohammedehab2002,2020-12-18], [user:namanbansal013,2020-12-19], [user:Redux,2020-12-19] for their time and great feedback. Also big thanks to Bytedance instructors [user:chenjb,2020-12-18] and [user:MiFaFaOvO,2020-12-18] for testing and r...
**Final update**: thanks for participating, hope you had fun! Let's hear it for the winners:

Full text and comments »

  • Vote: I like it
  • +492
  • Vote: I do not like it

83.
I finally became IGM — please don't spend years hating yourself for failures
By plagues, history, 2 months ago, In English
I finally became IGM — please don't spend years hating yourself for failures Hello everyone! A couple of days ago I finally reached IGM, and you cannot even imagine how happy I am. I want to tell you a bit about my journey. In 8th grade I got my first prize diploma at ROI. That was a pretty cool achievement, but I always wanted to be better. I had three whole years ahead of me to become a winner, yet I never managed to do it. My competitive programming career has been full of disappointments. The only year when I truly believed in myself was 8th grade. I was top 2 at IATI Junior by a huge margin, got my first VKOSHP diploma, became a ROI prizewinner, and overall progressed very fast. For example, that was when I reached 2100 on Codeforces for the first time. As you can see, it took me another 5 years just to finally become a grandmaster. In 9th grade, my team and I got top 5 at VKOSHP. For me it was a huge tilt, because it was the first “not gold” result after I had been dreaming about gold for so long. In 10th grade I was supposed to particip...
Now that I started writing rounds purely for fun, I stopped looking at a problem as a threat. Now

Full text and comments »

  • Vote: I like it
  • +481
  • Vote: I do not like it

84.
Codeforces Round #947 (Div. 1 + Div. 2)
By Bazoka13, 2 years ago, In English
Codeforces Round #947 (Div. 1 + Div. 2) Hello, Codeforces! Or, as we like to say in Servalish (created by [user:Serval,2024-05-24]): High-low, Cold-for-seize! We are glad to invite you to participate in [contest:1975], which will start on [contest_time:1975]. The round is a combined round and will be rated for everyone. The problems are prepared by [user:Atomic-Jellyfish,2024-05-24], [user:Nerovix,2024-05-24], [user:SanweiTreap,2024-05-24], [user:Serval,2024-05-24], [user:Toxel,2024-05-24], [user:jhdonghj112,2024-05-24] and me. You will be given **9 problems** to solve in **3 hours**. Scoring distribution will be announced later. We would like to thank everyone that makes this round possible: - [user:errorgorn,2024-05-24] for his &#128056;, &#128561;, &#128077; and &#129398; coordination. - [user:Alexdat2000,2024-05-24] for Russian translation. - [user:BFLSTiger,2024-05-24] and [user:wzy2001wzy,2024-05-24] for providing some <s>rejected</s> problem proposals and discussing problems with us. - [user:2sozx,2024-...
We recommend you to read the statements of all problems. Good luck & Have fun! (=・ω・=)

Full text and comments »

  • Vote: I like it
  • +604
  • Vote: I do not like it

85.
How I Spent Two Hours of My Free Time Today
By Nyaan, history, 6 weeks ago, In English
How I Spent Two Hours of My Free Time Today I am one of the part-time staff members at AtCoder responsible for investigating cheating involving AI. Let me explain what happened during my free time today. ## What I did in my free time today I was browsing Codeforces blogs, as I often do for fun. I found a post asking AtCoder to unban a certain user. The banned user was also in the comments, strongly insisting that they had not cheated. The comment section was full of people criticizing AtCoder. I immediately reviewed the case again. The user had been banned yesterday for cheating that took place three months earlier. After carefully rechecking the evidence, I also concluded that they had clearly used AI. (I will not explain the details because they relate to our methods for detecting AI use. The same applies to the cases below.) The post also named another person who was said to have been falsely banned. I did not feel like spending even more time on this, but I carefully reviewed that case as well. That user had blat...
commenters kept making fun of AtCoder's banning system, without even knowing that we seriously review, I was browsing Codeforces blogs, as I often do for fun.

Full text and comments »

  • Vote: I like it
  • +486
  • Vote: I do not like it

86.
Codeforces Round 1049 (Div. 2)
By shorya1835, history, 12 months ago, In English
Codeforces Round 1049 (Div. 2) Hello, Codeforces! We are glad to invite you to participate in [Codeforces Round 1049 (Div. 2)](https://codeforces.me/contest/2140) on [contest_time:2140]. You will have $2$ hours to solve $6$ problems and some problems will be divided into subtasks. The round will be rated for participants whose rating is below **2100**, but higher rated users are also welcome to participate out of competition. The problems were authored and prepared by [user:shorya1835,2025-09-08], [user:divine_spark,2025-09-08] and [user:wakanda-forever,2025-09-08]. We would like to thank: - [user:Sugar_fan,2025-09-08] for his great coordination. - [user:Alexdat2000,2025-09-08] for Russian translation. - [user:doofushmirtz,2025-09-08], [user:Dragokj03,2025-09-08], [user:Shubham_KV,2025-09-08] and [user:ho-oh,2025-09-08], for proposing problems that later weren’t included in the final set. - Our list of testers for providing valuable feedback: [user:fallleaves01,2025-09-08], [user:_istil,2025-09-08...
Good luck & have fun!

Full text and comments »

  • Vote: I like it
  • +518
  • Vote: I do not like it

87.
Invitation to CodeChef December Lunchtime 2020
By Um_nik, history, 6 years ago, In English
Invitation to CodeChef December Lunchtime 2020 We invite you to participate in CodeChef’s [December Lunchtime](http://bit.ly/LTIME91-Codeforces), this **Saturday, 26th December**, from [9:30 pm to 12:30 am IST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=December+2020+Lunchtime&iso=20201226T2130&p1=44&ah=3). **Note the unusual time.** It starts at 9:30pm instead of the usual 7:30pm You will be given a total of **8 problems** (6 in Div2, 6 in Div1) to solve in a duration of **3 hours**. Joining us on the problem setting panel are: - Setters: Sahil [user:sahi1422,2020-12-25] Chimnani, Venkata [user:Nikhil_Medam,2020-12-25] Nikhil Medam, Áron [user:mraron,2020-12-25] Noszály, Nishant [user:nishant403,2020-12-25] Shah, Yogesh [user:SeismicToss,2020-12-25] Sharma, Hriday [user:the_hyp0cr1t3,2020-12-25], Divyam [user:divyamsingal01,2020-12-25] Singal, Bhavyesh [user:bhvdsi,2020-12-25] Desai - Tester: Rahul [user:amnesiac_dusk,2020-12-25] Dugar - Editorialist: Taranpreet [user:taran_1407,2020-12-25] Singh ...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +350
  • Vote: I do not like it

88.
Codeforces Round #793 (Div. 2)
By CoderAnshu, 4 years ago, In English
Codeforces Round #793 (Div. 2) Hi Codeforces! I am pleased to invite you to [Codeforces Round #793 (Div. 2)](https://codeforces.me/contest/1682 "Adhocforces Round"), which will take place on [contest_time:1682]. You will be given **6 problems** and **2 hours** to solve them. The round will be rated for participants of Division 2 with a rating lower than 2100. Division 1 participants can participate unofficially in the round. All problems in this round were prepared by me and [user:rivalq,2022-05-19]. We have worked on this round for a long time and hope you find every problem interesting. I would like to thank: - [user:antontrygubO_o,2022-05-19] for marvellous coordination of the round. - [user:errorgorn,2022-05-19], [user:kclee2172,2022-05-19], [user:AmShZ,2022-05-19], [user:nvmdava,2022-05-19], [user:TheScrasse,2022-05-19], [user:aryanc403,2022-05-19], [user:koderkushy,2022-05-19], [user:PurpleCrayon,2022-05-19], [user:nor,2022-05-19], [user:AlperenT,2022-05-19], [user:towrist,2022-05-19], [user:...
Good luck and have fun! See you in the standings. Make sure to read the statements very carefully.

Full text and comments »

  • Vote: I like it
  • +616
  • Vote: I do not like it

89.
April Fools Day Contest 2022
By Agnimandur, history, 4 years ago, In English
April Fools Day Contest 2022 With [user:Nickolas,2022-03-29] not writing a contest this year, [user:magnus.hegdahl,2022-03-29] and I have decided to take up this sacred duty :). We would like to invite everyone on Codeforces to the [contest: 1663]. Special thanks to [user:BucketPotato,2022-03-29] for volunteering to test this contest! The 10th April Fools Day Contest will take place on [contest_time:1663]. This is a joke competition in which solving the problem is often easier than figuring out what the actual task is. In this round you'll be given several weird problems and 2 hours to solve them. The contest will use ACM ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them), and it will be unrated. You can submit solutions in any language allowed by Codeforces, unless the problem says otherwise. To get an idea of what the contest will look like, you can check out the contests of the past years: [2012](https://codeforces.me/contest/171), [2013](htt...
Good luck, and have fun!

Full text and comments »

  • Vote: I like it
  • +538
  • Vote: I do not like it

90.
Algorithms Thread 9: Treaps (+ Gym Contest!)
By SecondThread, history, 6 years ago, In English
Algorithms Thread 9: Treaps (+ Gym Contest!) Algorithms Thread Episode 9: Treaps ================== Good morning everyone! [Episode 9 of AlgorithmsThread](https://youtu.be/6x0UlIBLRsc) comes out shortly after the Div2 round ends. This episode is on Treaps! It covers: - Fundamentals of Treaps - Splitting and Merging - Range reversing ... and more! I also decided to keep up the super-high quality style and made a [custom gym set](https://codeforces.me/gym/102787) with 5(+2) original problems to make sure you really understand everything that was covered in the lecture. The gym set will be released shortly after the lecture ends, and I hope that the problems will be challenging and fun, even for people who aren't seeing treaps for the first time. If you have any questions or suggestions, feel free to leave them below. I hope you enjoy the problem statements, and, in the spirit of the upcoming holiday, I'll leave you all with this: ![ ](http://wumbogames.github.io/cfPictures/GrimTreaper.png) <hr /> Update:...
ends, and I hope that the problems will be challenging and fun, even for people who aren't seeing, , and I hope that the problems will be challenging and fun, even for people who aren't seeing treaps

Full text and comments »

  • Vote: I like it
  • +969
  • Vote: I do not like it

91.
Rayan 2024 Selection Round (Div. 1 + Div. 2, Rated, Prizes!)
By ArshiaDadras, 21 month(s) ago, In English
Rayan 2024 Selection Round (Div. 1 + Div. 2, Rated, Prizes!) &#128075; Salam, Codeforces! ------------------ <img src="/predownloaded/10/20/1020443c4ada8a8d0aeaa46f6dd4a34120fe8030.png" style="width: 30.0%;float: right;margin: 0 0.5em 0.5em 0.5em;max-width: 100.0%;max-height: 100.0%;"> We are thrilled to invite you to the [contest:2034]. The **Selection Round** is a rated contest for Div. 1 + Div. 2, taking place on [contest_time:2034]. The problems for this round were crafted and prepared by [user:ArshiaDadras,2024-11-19], [user:MohammadParsaElahimanesh,2024-11-19], [user:AmShZ,2024-11-19], [user:AmirrzwM,2024-11-19], and [user:Keshi,2024-11-19]. The **top 60 trusted participants** (with a maximum of three from each country) will qualify for the onsite **Final Round** in Tehran, in Spring 2025. An additional quota is reserved for the host country. Hotel accommodation, local transportation, and meals will be provided to all finalists. More details about the final contest will be available on the [Rayan](https://rayan.global/) website. ...
Good Luck & Have Fun! 🎉

Full text and comments »

  • Vote: I like it
  • +546
  • Vote: I do not like it

92.
Codeforces LATOKEN Round 1 (Div. 1 + Div. 2)
By Dormi, 5 years ago, In English
Codeforces LATOKEN Round 1 (Div. 1 + Div. 2) Hello, Codeforces! Welcome to the [contest:1534] supported by LATOKEN, that will start on [contest_time:1534]. It will be a combined rated round for both divisions (and div 3). **Please, note the unusual start time.** All problems were created by [user:Aaeria,2021-06-09], [user:crackersamdjam,2021-06-12], [user:Dormi,2021-06-09], [user:Ninjaclasher,2021-06-09], and [user:Plasmatic,2021-06-09]. We would like to thank: - Valentin Preobrazhenskiy from LATOKEN supporting the round. - [user:300iq,2021-06-10] and [user:kan,2021-06-10] for coordinating the round and answering our relentless questions. - [user:arvindr9,2021-06-09], [user:delmos,2021-06-09], [user:duality,2021-06-09], [user:growup974,2021-06-09], [user:m371,2021-06-09], [user:purplecrayon,2021-06-09], [user:rkm62,2021-06-09], [user:socho,2021-06-09], [user:wleung_bvg,2021-06-09], and [user:zeyu,2021-06-09] for their invaluable advice and suggestions. - [user:MikeMirzayanov,2021-06-09] for great systems Codeforces...
interesting! Good luck, have fun, and we wish everyone high ratings!

Full text and comments »

  • Vote: I like it
  • +638
  • Vote: I do not like it

93.
Cognition @ IOI 2026
By tourist, 4 weeks ago, In English
Cognition @ IOI 2026 Cognition is sponsoring the IOI this year! [user:ecnerwala,2026-08-08], [user:tourist,2026-08-08], [user:skittles1412,2026-08-08], and [user:walnutwaldo20,2026-08-08] will all be there. We'll have a booth in the Fun Zone after both contest days, and we'll generally be hanging around throughout the week. Come by and say hi, we'd love to meet you! Competitive programming runs deep at Cognition. Many of our engineers competed in high school olympiads, and our founders ([user:scott_wu,2026-08-08], [user:stevenkplus,2026-08-08], and [user:walnutwaldo20,2026-08-08]) are all IOI gold medalists. One fun fact: every IOI from 2006 through 2025 had at least one Cognition employee competing in it. Today, Cognition is one of the largest AI startups in the world. We're building the future of software engineering and working with Fortune 500 companies to transform how they build software. We hope to see you in Tashkent. Until then, here's a fun warmup problem :) <spoiler summary="Problem"...
[user:walnutwaldo20,2026-08-08]) are all IOI gold medalists. One fun fact: every IOI from 2006 through 2025 had, booth in the Fun Zone after both contest days, and we'll generally be hanging around throughout the, We hope to see you in Tashkent. Until then, here's a fun warmup problem :)

Full text and comments »

  • Vote: I like it
  • +521
  • Vote: I do not like it

94.
Japanese Olympiad in Informatics (JOI) Spring Camp 2020
By yutaka1999, history, 6 years ago, In English
Japanese Olympiad in Informatics (JOI) Spring Camp 2020 Hello Everyone! Japanese Olympiad in Informatics Spring Camp 2020 will be held from Mar. 19 to Mar. 23. There will be four online mirror contests during the camp. - day1 : [Mar. 20 (01:00 — 06:00 GMT)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympiad+in+Informatics+Spring+Camp+2020&iso=20200320T10&p1=248&ah=5) or [Mar. 20 (07:30 — 12:30 GMT)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympiad+in+Informatics+Spring+Camp+2020&iso=20200320T1630&p1=248&ah=5) - day2 : [Mar. 21 (01:00 — 06:00 GMT)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympiad+in+Informatics+Spring+Camp+2020&iso=20200321T10&p1=248&ah=5) or [Mar. 21 (07:30 — 12:30 GMT)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympiad+in+Informatics+Spring+Camp+2020&iso=20200321T1630&p1=248&ah=5) - day3 : [Mar. 22 (01:00 — 06:00 GMT)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympiad+in+Informatics+...
We welcome all participants. Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +458
  • Vote: I do not like it

95.
IAEPC Preliminary Contest (Codeforces Round 999, Div. 1 + Div. 2)
By EvenImage, history, 19 months ago, In English
IAEPC Preliminary Contest (Codeforces Round 999, Div. 1 + Div. 2) Hello, Codeforces! We are pleased to invite you to [contest:2061]. The Preliminary Contest is a rated contest for Div. 1 + Div. 2, taking place on [contest_time:2061]. The problems for this round were prepared by [user:jqdai0815,2025-01-18] and [user:orzdevinwang,2025-01-18]. The top 50 contestants at least 18 years old will be invited to participate in the onsite finals. We will cover the travel expenses for onsite contestants. The finals are scheduled to take place in CUHK from February 27 to March 2, 2025. The prizes for first place, second place, and third place of the onsite final are 10000, 5000, and 3000 USD. More prizes and detailed information will be announced soon. You can visit [International AI Elite Programming Contest](https://iaepc.global/) for information. We would like to thank: - [user:MikeMirzayanov,2025-01-18] for the Codeforces and Polygon platforms. - [user:Sugar_fan,2025-01-18] for coordinating the round. - [user:Kevin114514,2025-01-20], ...
We hope you enjoy this round. Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +322
  • Vote: I do not like it

96.
Codeforces Round 968 (Div. 2)
By zltzlt, history, 2 years ago, In English
Codeforces Round 968 (Div. 2) (After 3 months) Hello again, Codeforces! We are glad to invite you to participate in [contest: 2003], which will start on [contest_time: 2003]. You will be given **6 problems** and **2 hours** to solve them. Two problems are divided into two subtasks. This round will be **rated** for participants whose rating is **below 2100**. Participants with higher rating can participate unofficially. The problems were authored and prepared by me. I would like to thank: - [user: 244mhq, 2024-8-23] for perfect coordination. - [user: A_G, 2024-8-23], [user: wutongchun, 2024-8-23], [user: yeminghan, 2024-8-23] for red testing. - [user: DisconnectedGraph, 2024-8-23], [user: small_peter, 2024-8-23], [user: JWRuixi, 2024-8-23] for orange testing. - [user: yinhee, 2024-8-23], [user: QwQwf, 2024-8-23], [user: Jryno1, 2024-8-23], [user:sinsop90,2024-08-23] for purple testing. - [user: dieselhuang, 2024-8-23], [user: WRuperD, 2024-8-23], [user: CSQ31, 2024-8-23], [user: gdf_yhm, 2024-8-23...
Good luck & Have fun!

Full text and comments »

  • Vote: I like it
  • +449
  • Vote: I do not like it

97.
Codeforces Round #632 (Div. 2)
By PuRpLe_FoReVeR, 6 years ago, In English
Codeforces Round #632 (Div. 2) Hello, Codeforces! I'm glad to invite you to my first round [contest:1333], which will take place on [contest_time:1333]. "Thank you" time! I'd like to thank: - [user:antontrygubO_o,2020-04-05] for coordination of the round. - [user:300iq,2020-04-05], [user:nvmdava,2020-04-05], [user:aryanc403,2020-04-05], [user:antoshkin,2020-04-05], [user:lkosten,2020-04-05], [user:pavel-afonkin,2020-04-05] for testing and useful advices. - [user:MikeMirzayanov,2020-04-05] for great systems Codeforces and Polygon. - [user:CuriOusQuOkka,2020-04-05] for listening to my mumble while I came up with tasks. - [user:antontrygubO_o,2020-04-05] for coordination of the round (again). You'll be given 6 problems and 2 hours to solve them. Point distribution will be announced as soon as possible. Hope you will enjoy the round! Good luck and have fun! **P.S: YES, IT'S RATED.** **UPD**: Score distribution: 500 &mdash; 750 &mdash; 1250 &mdash; 1750 &mdash; 2000 &mdash; 2500. **U...
Hope you will enjoy the round! Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +878
  • Vote: I do not like it

98.
Codeforces Round 1034 (Div. 3)
By reirugan, 14 months ago, In English
Codeforces Round 1034 (Div. 3) Hello, Codeforces! ================== I am very excited to invite you to my first-ever contest, [contest:2123], which will start on [contest_time:2123]! In this contest, you will be given **2 hours and 15 minutes** to solve **7 problems**. The round will be hosted by the rules of educational rounds (extended ICPC). Thus, all solutions will be judged on preliminary tests during the round, and after the round, there will be a 12-hour phase of **open hacks**. After the open hack phase, all accepted solutions will be rejudged on successful hacks. Also, note that there is no score distribution &mdash; rank will be determined by number of problems solved, followed by penalty; wrong submissions will incur the usual penalty of **10 minutes**, following the rules of educational rounds. [As a reminder](https://codeforces.me/blog/entry/59228), only trusted participants of the third division will be included in the official standings table. This is a compulsory measure for combating unspo...
Good luck, and have fun!

Full text and comments »

  • Vote: I like it
  • +478
  • Vote: I do not like it

99.
AIM Tech Poorly Prepared Contest (unrated, funny, div. 1 preferred)
By Kostroma, 7 years ago, In English
AIM Tech Poorly Prepared Contest (unrated, funny, div. 1 preferred) Hello! Traditionally AIM Tech organizes a big party for Petrozavodsk camp participants to have fun and get an opportunity to communicate with each other. Usually it comes along with **a funny contest in unusual format**. This year we decided to share the fun with all codeforces community! This year we came up with a format requiring (probably) less time for preparing the contest. It is somewhat similar to an ordinary contest with a 3-hour duration. We already have some problem ideas, so it should be super easy to prepare the problems just one night before the competition. We hope everything will run smoothly! The contest will start on [contest_time:1302]. It could be a bit rescheduled due to onsite delays. It will be **an unrated funny competition**. Unlike usual ICPC-style contests, you'll be given an archive with several open test cases and answers for each problem. You'll have some sample test cases in the statement too, they'll be included in the archive. However, the ...
Traditionally AIM Tech organizes a big party for Petrozavodsk camp participants to havefun and get, fun!

Full text and comments »

  • Vote: I like it
  • +424
  • Vote: I do not like it

100.
Codeforces Round 1116 (Div. 1, Div. 2)
By paulzrm, 4 weeks ago, In English
Codeforces Round 1116 (Div. 1, Div. 2) Hello, Codeforces! We are glad to invite you to participate in [contest:2255] and [contest:2256] on [contest_time:2256]. The round will be rated for participants from both divisions. You will be given **6 problems** and **2 hours and 30 minutes** to solve them. At least one of the problems will be divided into subtasks. Please note that this contest contains **at least one run-twice (communication) problem**. Please read the guides for [run-twice problems](https://codeforces.me/blog/entry/147996) before the contest if you are unfamiliar with them. All problems were authored and prepared by [user:Error_Yuan,2026-08-04] and me, [user:paulzrm,2026-08-03]. More than eight years after [Codeforces Round 449](https://codeforces.me/blog/entry/56101), **Chtholly Nota Seniorious — the happiest girl in the world — is returning to Codeforces!** In this round, you will once again meet Chtholly, Nephren, Ithea, Willem, and other characters from [What Do You Do at the End of the W...
**Good luck and have fun!**

Full text and comments »

  • Vote: I like it
  • +445
  • Vote: I do not like it

101.
Codeforces Round #800
By AmShZ, 4 years ago, In English
Codeforces Round #800 Hi Codeforces! [user:Keshi,2022-06-13], [user:alireza_kaviani,2022-06-13] and I are delighted to invite you to participate in [contest:1693] and [contest:1694]. - Start time: [contest_time:1693] - Duration: $120$ minutes - Number of Tasks: $6$ for both divisions - Rated range: ($-\infty$,$1899$] for Div2, [$1900$, $\infty$) for Div1 We are honored to have set the 800th Codeforces round. We wish this wonderful platform all the best along with many other exciting rounds. Huge thanks to the following people: - [user:antontrygubO_o,2022-06-13] for his breath-taking coordination. - Our testers [user:um_nik,2022-06-13], [user:errorgorn,2022-06-13], [user:koosha_mv,2022-06-13], [user:irkstepanov,2022-06-13], [user:ArchUser84,2022-06-13], [user:sohsoh,2022-06-13], [user:fatemetmhr,2022-06-13], [user:Dorost,2022-06-13], [user:nor,2022-06-13], [user:pooya-shams,2022-06-13], [user:Arnch,2022-06-13], [user:Kahou,2022-06-13] and [user:mosaev,2022-06-13] for testing the round an...
luck have fun to everyone!

Full text and comments »

  • Vote: I like it
  • +796
  • Vote: I do not like it

102.
Codeforces Round #912 (Div. 2)
By Theo830, 3 years ago, In English
Codeforces Round #912 (Div. 2) Γεια σου (Hello), Codeforces once again! [user:Adam_GS,2023-11-25] and I are glad to invite you to participate in [Codeforces Round #912 (Div. 2)](https://codeforces.me/contest/1903) which will take place on [contest_time:1903]. **Note the unusual start time of the round**. As usual, **this round will be rated for participants with rating lower than 2100.** Problems were created and prepared by [user:Adam_GS,2023-11-25] and me. We tried to make them interesting, with short and clear statements. We hope that you will enjoy them! I would like to thank: - [user:ScarletS,2023-11-25] for amazing coordination of this round. - [user:Adam_GS,2023-11-25] for joining as an author after testing the contest. - [user:fishy15,2023-11-25], [user:Andreasyan,2023-11-25], [user:phattd,2023-11-25], [user:Murinh0,2023-11-25], [user:irkstepanov,2023-11-25], [user:wuhudsm,2023-11-25], [user:Ari,2023-11-25], [user:satyam343,2023-11-25], [user:Qualified,2023-11-25], [user:nyaruhod...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +463
  • Vote: I do not like it

103.
April Fools Day Contest 2021
By Nickolas, 5 years ago, In English
April Fools Day Contest 2021 The contest is over; I hope you enjoyed it! The editorial is available [here](https://codeforces.me/blog/entry/89260). --- The 9th April Fools Day Contest will take place on Thursday [April 1st](https://www.timeanddate.com/worldclock/fixedtime.html?day=1&month=4&year=2021&hour=17&min=35&sec=0&p1=166). This is a joke competition in which solving the problem is often easier than figuring out what the actual task is. In this round you'll be given several weird problems and 2 hours to solve them. The contest will use ACM ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them), and it will be unrated. You can submit solutions in any language allowed by Codeforces, unless the problem says otherwise. To get an idea of what the contest will look like, you can check out the contests of the past years: [2012](http://codeforces.me/contest/171), [2013](http://codeforces.me/contest/290), [2014](http://codeforces.me/contest/409),...
Good luck, and have fun!

Full text and comments »

  • Vote: I like it
  • +781
  • Vote: I do not like it

104.
JOI Spring Training 2024 Online Contest
By E869120, 2 years ago, In English
JOI Spring Training 2024 Online Contest Hello, everyone! [Japanese Olympiad in Informatics (JOI) Spring Training 2024](https://contests.ioi-jp.org/joi-sp-2024/index-en.html) will be held from March 21 to March 24. There are **4 days** in the contest. * Day 1: [March 21, 02:00 GMT &mdash; March 21, 24:00 GMT](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympiad+in+Informatics+%28JOI%29+Spring+Camp+2024+Day1&iso=20240321T02&p1=1440&ah=22) * Day 2: [March 22, 02:00 GMT &mdash; March 22, 24:00 GMT](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympiad+in+Informatics+%28JOI%29+Spring+Camp+2024+Day2&iso=20240322T02&p1=1440&ah=22) * Day 3: [March 23, 02:00 GMT &mdash; March 23, 24:00 GMT](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympiad+in+Informatics+%28JOI%29+Spring+Camp+2024+Day3&iso=20240323T02&p1=1440&ah=22) * Day 4: [March 24, 02:00 GMT &mdash; March 24, 24:00 GMT](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympiad+in+Inf...
We welcome all participants. Good luck and have fun!

Full text and comments »

Tags joi, ioi
  • Vote: I like it
  • +359
  • Vote: I do not like it

105.
Codeforces Round 967 (Div. 2)
By Misuki, 2 years ago, In English
Codeforces Round 967 (Div. 2) Hello Codeforces! (你好, Codeforces!) [user:Kaey,2024-08-16] and I are glad to invite you to [contest:2001] which will start on [contest_time:2001]. The contest will last for 2 hours with 5 tasks for you to solve, and 1 task will have subtasks. The contest will only be rated for those with a rating not higher than 2099, but higher rated users are also more than welcome to participate out of competition. There is at least one interactive problem, so please read [the guide for interactive problems](https://codeforces.me/blog/entry/45307) if you are unfamiliar with them. Holding the contest would have been impossible without the help from: - [user:Kaey,2021-08-16] for supercalifragilisticexpialidocious coordination. - [user:feecle6418,2024-08-17] for providing idea of one of the problem. - [user:BurnedChicken,2024-08-16], [user:cheissmart,2024-08-16], [user:SorahISA,2024-08-16], [user:WiwiHo,2024-08-16], [user:Fysty,2024-08-16], [user:Potassium,2024-08-16], [user:Emilan,2024-...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +420
  • Vote: I do not like it

106.
[Tutorial] Non-trivial DP Tricks and Techniques
By zscoder, history, 10 years ago, In English
[Tutorial] Non-trivial DP Tricks and Techniques Hi everyone! Today I want to share some DP tricks and techniques that I have seen from some problems. I think this will be helpful for those who just started doing DP. Sometimes the tutorials are very brief and assumes the reader already understand the technique so it will be hard for people who are new to the technique to understand it. Note : You should know how to do basic DP before reading the post DP + Bitmasks ------------------ This is actually a very well-known technique and most people should already know this. This trick is usually used when one of the variables have very small constraints that can allow exponential solutions. The classic example is applying it to solve the Travelling Salesman Problem in $O(n^{2} \cdot 2^{n})$ time. We let $dp[i][j]$ be the minimum time needed to visit the vertices in the set denoted by $i$ and ending at vertex $j$. Note that $i$ will iterate through all possible subsets of the vertices and thus the number of states is $O(2^{n} \cdo...
/data-science-tutorials/a-bit-of-fun-fun-with-bits/) for how to iterate through all subsets of a

Full text and comments »

  • Vote: I like it
  • +612
  • Vote: I do not like it

107.
Codeforces Round #459
By PrinceOfPersia, history, 9 years ago, In English
Codeforces Round #459 I'm honored to announce that Codeforces round #459 is going to take place on [January 29th](http://www.timeanddate.com/worldclock/fixedtime.html?day=29&month=1&year=2018&hour=17&min=35&sec=0&p1=166) and [user:Reyna,2018-01-27] and I are the problemsetters of this round. I'd like to thank [user:keyvankhademi,2018-01-27], [user:AlexFetisov,2018-01-27], [user:winger,2018-01-29], [user:Belonogov,2018-01-29], [user:cyand1317,2018-01-29] and [user:demon1999,2018-01-29], [user:AnPelec,2018-01-29] for testing, [user:KAN,2018-01-27] for coordinating the round and [user:MikeMirzayanov,2018-01-27] for the great Codeforces and Polygon platforms. The main characters of the round are Stranger Things characters. ![ ](/predownloaded/d3/f5/d3f5221e709404a97973b24602a88449e161a4d7.png) The scoring distribution will be announced soon. Good luck and have fun. **UPD0:** The round is over, we hope you enjoyed it. Editorial will be posted soon. **UPD1:** System testing is over, congratul...
Good luck and have fun.

Full text and comments »

  • Vote: I like it
  • +750
  • Vote: I do not like it

108.
Codeforces Round #250
By vfleaking, 12 years ago, In English
Codeforces Round #250 Happy Children's Day everyone. What should you do to celebrate the special holiday? Of course, another Codeforces Round is your best choice! There is a child who is our friend. Now he has faced a lot of algorithm problem, could you please help him? ![ ](http://tb2.bdstatic.com/tb/editor/images/qpx_n/b37.gif?t=20140529) We invite you to participate in Codeforces Round #250, which will take place at [17:00 MSK on 6.1 &mdash; Children's Day](http://www.timeanddate.com/worldclock/fixedtime.html?day=1&month=6&year=2014&hour=17&min=0&sec=0&p1=166). This round will be held in both divisions. Note that the starting time of this round is quite unusual.Why? Because it's yet another CF Round held by Chinese! We prepared many interesting problems for you. Are you getting excited? Don't miss this round! The problems were prepared by [user:Delayyy,2014-05-31], [user:Picks,2014-05-31] and me. This is our first Codeforces round~~~~. Many thanks to [user:Gerald,2014-05-31], wh...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +557
  • Vote: I do not like it

109.
Codeforces Round #715 Editorial
By Ari, history, 5 years ago, In English
Codeforces Round #715 Editorial <strike>Note: I can't figure out how to place the tutorials inside spoilers. If someone is familiar with how CF spoilers work and can help I would really appreciate it. For now, be warned that the tutorials are visible by default (but everything else isn't)</strike> **UPD:** I figured out how to use spoilers! Also added implementations for all problems. Thanks for participating in our contest! [problem:1509A] Author: [user:Kuroni,2021-04-13] <br> First solve: [user:cfg0d,2021-04-16] at 00:01:02 <spoiler summary = "Hint"> How can you write the condition that $\frac{a_u + a_v}{2}$ is an integer in a more useful way? Think of the parities. </spoiler> <spoiler summary = "Tutorial"> [tutorial:1509A] </spoiler> <spoiler summary = "Comments from the authors"> ![ ](https://i.imgur.com/voR4hTu.png) </spoiler> [Implementation](https://codeforces.me/contest/1509/submission/113263196) [problem:1509B] Author: [user:Ari,2021-04-13] <br> First solve: [user:bl...
One more fun fact for your consideration: This problem's name in Polygon is "sorrow".

Full text and comments »

  • Vote: I like it
  • +413
  • Vote: I do not like it

110.
Order Capital Intro
By -XraY-, history, 14 months ago, In English
Order Capital Intro <img alt="Order Capital" src="/predownloaded/00/3e/003eef1043e9506ad4620583c5be192631830899.png" style="float:right;height: 200px; margin: 10px; max-width:40%;"/> Hello everyone! I invite you to take part in [contest:2122]. My name is Igor Pyshkin. Throughout my academic career, I participated in a lot of programming and math competitions: I am the 2016 ACM ICPC World Champion and competed in the onsite finals of the Facebook Hacker Cup, Google Code Jam, and TopCoder Open. After completing my degree, I transitioned into a new field — high-frequency trading (HFT). Four years ago, I founded my own HFT fund — [Order Capital](https://ordercapital.com/). Since then together with my colleagues I have been working really hard to reach the highest levels of the HFT industry. Launching this contest on Codeforces is quite special to me, as it is our first contest on the platform as a company. I would like to thank the Codeforces team and everyone involved in the round preparation...
This is our debut contest — and we’ve worked hard to make it fun, fair, and memorable. We hope, We loved working on this round and hope it’s fun for you. If you’re curious about what we do at

Full text and comments »

  • Vote: I like it
  • +438
  • Vote: I do not like it

111.
VK Cup 2017 Round 1 and CF Round 405 div1+div2
By Errichto, 9 years ago, In English
VK Cup 2017 Round 1 and CF Round 405 div1+div2 Hello. The round 1 of VK Cup 2017 will take place on March 18 at 18:35 MSK (check your timezone [here](https://www.timeanddate.com/worldclock/fixedtime.html?day=18&month=3&year=2017&hour=18&min=35&sec=0&p1=166)), along with standard div1+2 Codeforces Round \#405. The contest "VK Cup 2017 &mdash; Round 1" is for teams qualified from two Qualification Rounds. The top 400 teams will advance to the Round 2, while other ones will have one more chance in the Wild Card Round 1 in April. Those who don't participate in the VK Cup can take part in the Codeforces Round \#405 individually (problems will be available in English too). All three rounds last 2 hours, and all are rated. I want to thank: [user:KAN,2017-03-17] for his help in the contest preparation, [user:MikeMirzayanov,2017-03-17] that we are here, [user:AlexFetisov,2017-03-17] for testing, the VK company for this nice annual contest. I'm a setter and I hope (and expect?) that you will enjoy the problems. During the conte...
I wish you great fun and no frustrating bugs.

Full text and comments »

Announcement of VK Cup 2017 - Round 1
  • Vote: I like it
  • +286
  • Vote: I do not like it

112.
Codeforces Round #654 (Div. 2)
By physics0523, history, 6 years ago, In English
Codeforces Round #654 (Div. 2) Codeforcesの皆さん、こんにちは!(Hello, Codeforces!) I'm glad to invite you to my first contest, [contest:1371] which will be held on [contest_time:1371] (notice **earlier time** than usual). All of the problems were mainly written and prepared by me. The round is **rated if your rating is strictly less than 2100**. You will be given **6 problems** (one problem has a subtask) and **2 hours** to solve them. Please, read all the problems. I would really like to thank: - [user:isaf27,2020-06-30] for amazing coordinating my round. - [user:300iq,2020-06-30] , [user:alireza_kaviani,2020-06-30] , [user:AmShZ,2020-06-30] , [user:antontrygubO_o,2020-06-30] , [user:dorijanlendvaj,2020-06-30] , [user:lucky_21,2020-06-30] , [user:Monogon,2020-06-30] , [user:noobiesAG,2020-06-30] , [user:sibasish_14,2020-06-30] and [user:zxyl,2020-06-30] for mighty testing the problems. - [user:MikeMirzayanov,2020-06-30] for marvelous Codeforces and Polygon platforms. The scoring distribution will be announce...
Good luck, have fun and wish your high ratings :)

Full text and comments »

  • Vote: I like it
  • +732
  • Vote: I do not like it

113.
Hybrid Tutorial #-1: Heavy-Light Decomposition
By galen_colin, 6 years ago, In English
Hybrid Tutorial #-1: Heavy-Light Decomposition **[Here](https://www.youtube.com/watch?v=_G_LMuLWMaI&list=PLDjGkpToBsYDx4GWu2u87sTqt6ICELz-T) is a playlist of all hybrid tutorials I've done.** # "Intro" _Timestamp: [00:00](https://youtu.be/_G_LMuLWMaI)_ Hi! Definitely not inspired by [this comment](https://codeforces.me/blog/entry/81086?#comment-675431), I've decided to try something that seems relatively novel &mdash; combining a blog and video tutorial into one, in a "hybrid" fashion. Both should be usable independently, but they will have the same "flow" and structure so you can reference both for concepts that are harder to grasp, and the two will supplement each other. The goal of these is to be **complete** &mdash; beneficial for both video and blog lovers, as well as full of enough information that anyone without much of an idea of what the concept is should be able to fully understand. There will be code as well, however, I very highly recommend not looking at it, but rather working out the implementation for yours...
This is the fun part. I'll break this up into sections. The tree is always rooted arbitrarily (at 0).

Full text and comments »

  • Vote: I like it
  • +404
  • Vote: I do not like it

114.
Codeforces Month of Blog Posts (win $300)
By peltorator, 4 years ago, In English
Codeforces Month of Blog Posts (win $300) **TL;DR:** Write an interesting CodeForces blog post until February 15th and win $300. **UPD: Second place will receive $50.** **UPD2: Competition is over, The results are available [here](https://codeforces.me/blog/entry/113041).** I am a huge fan of CodeForces and specifically CodeForces blog posts! There are tens and hundreds of gems posted on this platform throughout the years. Thankfully, recently there was added the [catalog](https://codeforces.me/catalog) page where a lot of cool articles can be found. Personally, if I want to remember some classical algorithm, I would go to websites like [cp-algorithms](https://cp-algorithms.com/), but CodeForces is the place where new or rare stuff is born, where new points of view emerge. I think it is one of the most valuable functions of this website, and I would like to facilitate its growth. I know that many people have cool ideas in their minds that they came up with or maybe something that is known only in their community on ...
just a little motivation for you and the point of this is not money per se but fun.

Full text and comments »

  • Vote: I like it
  • +579
  • Vote: I do not like it

115.
Invitation to Codeforces Round 962 (Div. 3)
By cry, 2 years ago, In English
Invitation to Codeforces Round 962 (Div. 3) <center> Hewwo Cowodeforcers! ------------------ </center> [user:sum,2024-07-04] and I are overjoyed to welcome you to participate in [contest:1996] on [contest_time:1996]. This contest is the last stop on our mission to problemset for every division. We hope you've been enjoying our stuff so far! The round will be hosted by rules of educational rounds (extended ICPC). Thus, solutions will be judged on preliminary tests during the round, and after the round, it will be a 12-hour phase of **open hacks**. After open hacks all accepted solutions will be rejudged on successful hacks. You will be given **7 problems** and **2 hours and 15 minutes** to solve them. Note that the **penalty** for each wrong submission in this round is **10 minutes**. [Remember](https://codeforces.me/blog/entry/59228) that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsp...
Thank you for reading and we hope you have a fun and educational interstellar adventure :3

Full text and comments »

  • Vote: I like it
  • +423
  • Vote: I do not like it

116.
Grakn Forces 2020 [Div1 and Div2 combined]
By isaf27, history, 6 years ago, In English
Grakn Forces 2020 [Div1 and Div2 combined] Hello, Codeforces! <center> <img alt="grakn" src="https://grakn.ai/assets/svg/logo.svg" style="float:right; height: 50px; margin: 10px; max-width:10%;"/> </center> I'm glad to invite you to [contest:1408], which will be held on [contest_time:1408]. It will be **combined rated** round for **both divisions**. This round is initiated and supported by Grakn Labs. More information you could find [here](https://codeforces.me/blog/entry/82787). All problems were authored and prepared by [user:300iq,2020-09-29] and [user:isaf27,2020-09-29]. Thanks to [user:growup974,2020-09-29], [user:postscript,2020-09-29], [user:QAQAutoMaton,2020-09-29], [user:PM11,2020-09-29], [user:morzer,2020-09-29], [user:qlf9,2020-09-29], [user:RedDreamer,2020-09-29], [user:gdb_18,2020-09-29], [user:talibmohd,2020-09-29], [user:Dragnoid99,2020-09-29], [user:KAN,2020-09-29] and [user:VladGanzha,2020-09-29] for testing problems and good advice. Thanks to [user:MikeMirzayanov,2020-09-29] for great systems ...
problems. Good luck, have fun and we wish everyone high ratings!

Full text and comments »

Announcement of Grakn Forces 2020
  • Vote: I like it
  • +506
  • Vote: I do not like it

117.
Codeforces Round 1023 (Div. 2)
By sunkuangzheng, 16 months ago, In English
Codeforces Round 1023 (Div. 2) Hello, Codeforces! [user:auiunu,2025-04-30], [user:nahc0el,2025-04-30] and me are glad to invite you to the last round with 10 binary bits &mdash; [contest:2107], which will start on [contest_time:2107]. You will be given 6 problems and 1 subtask with 2 hours 15 minutes to solve them. The round will be rated for participants of Division 2 with a rating lower than 2100. Division 1 participants can participate unofficially. All problems are authored by [user:auiunu,2025-04-30], [user:nahc0el,2025-04-30] and me. We would like to thank: - [user:Dominater069,2025-04-30] and [user:TheScrasse,2025-04-30] for their wonderful coordination and huge help in preparing the round. - [user:Alexdat2000,2025-05-02] for the Russian translations. - [user:hyman00,2025-04-30], [user:le0n,2025-04-30], [user:Flamire,2025-04-30], [user:jeroenodb,2025-04-30] for LGM testing. - [user:Sana,2025-04-30], [user:N_z__,2025-04-30], [user:Wuyanru,2025-04-30], [user:Halzion,2025-04-30], [user:platter,...
We hope you will enjoy and have fun in the contest. Good luck!

Full text and comments »

  • Vote: I like it
  • +478
  • Vote: I do not like it

118.
Codeforces Round #356
By Errichto, 10 years ago, In English
Codeforces Round #356 Hello Codeforces. The CF Round \#356 will happen on 8-th June ([exact time](http://www.timeanddate.com/worldclock/fixedtime.html?day=8&month=6&year=2016&hour=19&min=35&sec=0&p1=166)). You will get five problems to solve in two hours. The round is rated. I encourage you to read other problems if you don't like or can't solve something. The scoring distribution will be announced. [user:MikeMirzayanov,2016-06-06] and [user:GlebsHP,2016-06-06] make the round possible. Also, thanks for [user:Stonefeang,2016-06-06], [user:kostka,2016-06-06], [user:johnasselta,2016-06-06], [user:AlexFetisov,2016-06-07] and (more to be added?) for their amazing help. And I want to thank my girlfriend because there would be no Limak without her. It's my first standard round. Still, you should get nice interesting problems. You will meet Limak, who is usually a little polar bear. Here he is, preparing one of problems. ![ ](http://codeforces.me/predownloaded/91/95/91956cb0e92e3c0376634a6a1...
I wish you great fun and no frustrating bugs.

Full text and comments »

  • Vote: I like it
  • +687
  • Vote: I do not like it

119.
JOI Final Stage 2026 Online Contest
By E869120, 5 months ago, In English
JOI Final Stage 2026 Online Contest Hello, everyone! **Japanese Olympiad in Informatics (JOI) Final Stage 2026 ([Contest URL](https://contests.ioi-jp.org/joi-final-2026/index-en.html))** will be held from March 21st to 24th. There are 4 days in the contest. Note that the Final Stage is a kind of IOI selection camp, which is equivalent to Spring Training in 2025 or before. * Day 1: [March 21, 02:00 GMT &mdash; March 21, 24:00 GMT](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympiad+in+Informatics+%28JOI%29+Spring+Camp+2026+Day1&iso=20260321T02&p1=1440&ah=22) * Day 2: [March 22, 02:00 GMT &mdash; March 22, 24:00 GMT](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympiad+in+Informatics+%28JOI%29+Spring+Camp+2026+Day2&iso=20260322T02&p1=1440&ah=22) * Day 3: [March 23, 02:00 GMT &mdash; March 23, 24:00 GMT](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympiad+in+Informatics+%28JOI%29+Spring+Camp+2026+Day2&iso=20260322T02&p1=1440&ah=22) * Day 4: [Mar...
We welcome all participants. Good luck and have fun!

Full text and comments »

Tags joi, ioi
  • Vote: I like it
  • +297
  • Vote: I do not like it

120.
Codeforces Round #869
By adamant, history, 3 years ago, In English
Codeforces Round #869 Hi everyone! It's been a while since I set problems for Codeforces competitions, so I hope that you had sufficient opportunity to rest before dealing with my problems again. Oh, no-no, there's nothing to worry about! Probably! I promise! [user:jeroenodb,2023-04-25] and [user:adamant,2023-04-25] (that's me!) are happy to invite you to [contest:1817] and [contest:1818] which are going to take place at [contest_time:1817]. Participants with a rating strictly lower than 1900 will participate in Division 2, while participants with a rating of at least 1900 will participate in Division 1. All the problems are prepared by us, and we would like to thank: * [user:dario2994,2023-04-21] for rejecting sufficient amount of problems for me to be able to set [Oleksandr Kulkov Contest 3](https://codeforces.me/blog/entry/113801), for thorough and dedicated coordination and for suggesting one of the problem ideas for the round. * [user:izban,2023-04-21], [user:gamegame,2023-04-21], [user:t...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +318
  • Vote: I do not like it

121.
Rockethon 2015 Announcement
By Seyaua, 12 years ago, In English
Rockethon 2015 Announcement <a href="http://rocketfuel.com/"><img src="http://assets.codeforces.com/images/rockethon/HZ-LOGO-TAG-RGB-big.png" style="float:right;margin:0 2em 2em 2em;"/></a> Hello Codeforces community, I am happy to announce that [Rocket Fuel Inc.](http://rocketfuel.com/) will be hosting a Rockethon competition again! The contest is prepared by Rocket Fuel employees Eldar Bogdanov, Anton Lomonos, Lasha Lakirbaia, Alexander Ruff, Nikhil Goyal and me, Ievgen Soboliev. We hope everyone will find some interesting problems in the contest and everyone will have as much fun solving these problems as we had preparing them. Just like last year, the best participants will receive valuable prizes and top performers will get Rockethon 2015 T-shirts! Also, Rocket Fuel is interested in hiring people after this event, so please fill out the simple form during registration. About Rocket Fuel --------------------- Rocket Fuel is building technology platform to do automatic targeting and optimization of a...
some interesting problems in the contest and everyone will have as much fun solving these problems as, — we do fun things here like playing basketball, soccer, table tennis. I invite everybody to

Full text and comments »

  • Vote: I like it
  • +607
  • Vote: I do not like it

122.
Codeforces Round 1012 (Div.1, Div. 2, based on THUPC 2025 — Finals)
By fengzhengwei, 17 months ago, In English
Codeforces Round 1012 (Div.1, Div. 2, based on THUPC 2025 — Finals) There will, and there shall be a THU round! =========================================== Nihao Codeforces! After the unfortunate event which led to [contest:2081] and [contest:2082] being unrated last week, we’re back and stronger than ever! Tsinghua University’s Student Association of Algorithmic Competitions (THUSAAC) is pleased to invite you to participate in [contest:2089] and [contest:2090] on [contest_time:2090]. This round will be RATED for everyone. You will be given 2 hours and 30 minutes to solve 5 problems for division 1 and 6 problems for division 2, and two of each will have subtasks. **Note the unusual time of the round.** Our team of amazing problem setters include: [user:Iam1789,2025-03-20], [user:Ecrade_,2025-03-20], [user:E.Space,2025-03-20], [user:QuietBeautifulThoughts,2025-03-20], [user:gyh20,2025-03-20], [user:spiritualkhorosho,2025-03-20], [user:dapingguo8,2025-03-20], [user:myee,2025-03-20], [user:abruce,2025-03-20], [user:_lucien,2025-03-20]. Some of ...
We hope you will enjoy and have fun in the contest. Good luck.

Full text and comments »

  • Vote: I like it
  • +446
  • Vote: I do not like it

123.
All You Need is Randomly Guessing — How to Improve at Codeforces
By Zhtluo, history, 2 years ago, In English
All You Need is Randomly Guessing — How to Improve at Codeforces I hope [my previous blog](https://codeforces.me/blog/entry/126310) has convinced you that the best way to improve at Codeforces is to be more Russian, i.e. to improve your math capability. Unfortunately, humble mortals such as you and I are not gifted with the talent that esteemed Russian grandmasters such as 74TrAkToR had: _Surely, it is beneficial to have a code reference for many algorithms and data structures, but I also think that just superficially knowing the algorithm and maybe having implemented it once or twice before is sufficient to use it without a reference?_ _&mdash; Some other Codeforces grandmaster_ Therefore, in this blog I will explore the dark side of Russian-ness &mdash; randomly guessing &mdash; that is forsaken by every Russian grandmaster of the light side I know. However, it has been very helpful to me, and I hope that it serves you well, too. ## Example 1 I will start by using an example to demonstrate my thought process. This problem [1923C](h...
- *But guessing randomly is not fun!* I don't think it's fun, either. Unfortunately, given that

Full text and comments »

  • Vote: I like it
  • +431
  • Vote: I do not like it

124.
On Div2ABs
By errorgorn, 4 years ago, In English
On Div2ABs 2 years ago, [user:antontrygubO_o,2022-04-27] wrote [a blog](https://codeforces.me/blog/entry/75163) about div2ABs where he expressed his opinions that d2ABs should not be about "here is a statement, please implement what is written there". Thanks to him, the quality of d2ABs (and problem quality in general) have certainly improved. However, I still believe that there still quite large differences between how coordinators/problemsetters view d2ABs and how the intended participants view them. From the survey made by [user:kpw29,2022-04-27], we can see that most people agree that most people agree that we should **primarily** consider the target audience when proposing a task. I too think if a task is boring to div 1 contestants, we should not think of that as a reason to immediately disqualify a problem from being a d2A. ![ ](https://codeforces.me/predownloaded/70/b5/70b515da85a4dc3b362cf4eb0963dbd1fb642819.png) I think when people judge the interesting-ness of d2As, they try...
close the tab. Whats so fun about permutations guys. Leave them alone for div2ABs. These problems, easiest problems of a div2 round, made for div2 competitors. Well, it should be fun for div 1 competitors, example of a good d2A). The problem just asks if you know the fun fact that $\gcd(x,1)=1$ and $\text{lcm, [user:darkkcyan,2022-04-27]: I think that a round on Codeforces should be fun, and maybe, [user:darkkcyan,2022-04-27]: The difficulty is ok. For me it is not that fun to solve, but for, [user:m0fum0fu,2022-04-27]: simple statement with nice illustration. implementation not sofun., [user:sus,2022-04-27]: Even though this answer is just n, its was still fun figureing out how to

Full text and comments »

  • Vote: I like it
  • +330
  • Vote: I do not like it

125.
Codeforces Round 1065 (Div. 3)
By reirugan, 10 months ago, In English
Codeforces Round 1065 (Div. 3) <img src="https://c.tenor.com/G25fbL0QjmYAAAAd/tenor.gif" style="width: 400.0px;float: right;margin: 0 1.0em 1.0em 1.0em;max-width: 100.0%;max-height: 100.0%;"> Hello, Codeforces! ================== I am very excited to invite you to my second-ever contest, [contest:2171], which will start on [contest_time:2171]! In this contest, you will be given **2 hours and 30 minutes** to solve **7 problems, two of which have been split into subtasks**. The subtasks for a given problem are not necessarily placed adjacently in the problemset. The round will be hosted by the rules of educational rounds (extended ICPC). Thus, all solutions will be judged on preliminary tests during the round, and after the round, there will be a 12-hour phase of **open hacks**. After the open hack phase, all accepted solutions will be rejudged on successful hacks. Also, note that there is no score distribution &mdash; rank will be determined by number of problems solved, followed by penalty; wrong submissions...
Good luck, and have fun!

Full text and comments »

  • Vote: I like it
  • +389
  • Vote: I do not like it

126.
Codeforces Round 949 (Div. 2)
By zltzlt, history, 2 years ago, In English
Codeforces Round 949 (Div. 2) Hello, Codeforces! We are glad to invite you to participate in [contest: 1981], which will start on [contest_time: 1981]. **Note the unusual start time of the round**. You will be given **6 problems** and **2 hours** to solve them. This round will be **rated** for participants whose rating is **below 2100**. Participants with higher rating can participate unofficially. The problems were authored and prepared by [user: sinsop90, 2024-5-29], [user: yinhee, 2024-5-29] and me. I would like to thank: - [user: 244mhq, 2024-5-29] for his wonderful coordination. - [user: sinsop90, 2024-5-29] and [user: yinhee, 2024-5-29] for providing problem ideas and discussing the problems with me. - [user: AFewSuns, 2024-5-29] and [user: crazy_sea, 2024-5-29] for providing a better solution to one of the problems. - [user: Um_nik, 2024-5-29] for the only LGM testing. - [user: A_G, 2024-5-29], [user: antontrygubO_o, 2024-5-29], [user: StarSilk, 2024-5-29], [user: CharlieV, 2024-5-29], [us...
Good luck & Have fun!

Full text and comments »

  • Vote: I like it
  • +370
  • Vote: I do not like it

127.
Codeforces Round 1068 (Div. 2)
By paulzrm, 9 months ago, In English
Codeforces Round 1068 (Div. 2) Hello Codeforces! We are glad to invite you to participate in [contest:2173] on [contest_time:2173]. This round is rated for **all participants with rating below 2100**. You will be given **6 problems** and **2 hours** to solve them. **At least one problem will be interactive**, so please make sure to read the [guide for interactive problems](https://codeforces.me/blog/entry/45307) before the contest. In this contest, characters from four different anime series appear in some of the problem statements (including the one my avatar is from). Can you guess which series they are? We would like to thank: - [user:paulzrm,2025-12-02], [user:HHH666666,2025-12-02], [user:chen_zida,2025-12-02] and [user:Hugewide,2025-12-02] for writing the problems. - [user:Error_Yuan,2025-12-02] for coordinating the round. - [user:MikeMirzayanov,2025-12-02] for great Codeforces and Polygon platforms. - [user:Alexdat2000,2025-12-04] for translating the statements into Russian. - [user...
**Good Luck & Have Fun!**

Full text and comments »

  • Vote: I like it
  • +381
  • Vote: I do not like it

128.
Codeforces Round #676 (Div. 2)
By flaviu2001, history, 6 years ago, In English
Codeforces Round #676 (Div. 2) Hi Codeforces! [user:stefdasca,2020-10-17], ~koala_bear00,2020-10-14 and I are very excited to announce our first contest [Codeforces Round #676](https://codeforces.me/contest/1421), which will take place [contest_time:1421]. The round will be rated for participants with rating up to 2099. The tasks were written by me with help from [user:stefdasca,2020-10-14] and [user:koala_bear00,2020-10-14] and you have to help some of the authors' favorite musical artists to solve the problems they're faced with. We hope we compiled a very interesting contest with memorable tasks :) Special thanks to: * [user:antontrygubO_o,2020-10-14] for coordinating our round and pushing us to come up with more and more interesting tasks. * [user:dorijanlendvaj,2020-10-14], [user:kclee2172,2020-10-14], [user:Devil,2020-10-14], [user:thenymphsofdelphi,2020-10-14], [user:jainbot27,2020-10-14], [user:Stelutzu,2020-10-14], [user:proggerkz,2020-10-14], [user:SleepyShashwat,2020-10-14], [user:bh...
You will be given 2 hours to solve 5 problems, good luck everyone and have fun!

Full text and comments »

  • Vote: I like it
  • +564
  • Vote: I do not like it

129.
Congratulations to the winners of the 2nd Universal Cup Semifinal!
By kostka, 2 years ago, In English
Congratulations to the winners of the 2nd Universal Cup Semifinal! We’re excited to share that the **Universal Cup Summer Summit 2024**, sponsored by Huawei, just wrapped up in the beautiful Cancun, Mexico! ![ ](/predownloaded/2d/b9/2db998d0e500754097aab836010f4a903bf26bcf.jpg) ![ ](/predownloaded/d5/5f/d55f2cb20af1268fbb49cfde93c34a84fc93121d.jpg) ![ ](/predownloaded/8c/9b/8c9bda7ee471605ce6af0e80da5c9b979fd7d07e.jpg) The highlight of the event was the 2nd Universal Cup Semifinal, where 200 teams competed both onsite and online. A huge shoutout to all our onsite teams: **Gold Medal** * USA1 ([user:ecnerwala,2024-06-25], [user:ksun48,2024-06-25], [user:tourist,2024-06-25]) **Silver Medal** * Polish Mafia ([user:Swistakk,2024-06-25], [user:Radewoosh,2024-06-25], [user:Marcin_smu,2024-06-25]) **Bronze Medal** * HoMaMaOvO ([user:maroonrk,2024-06-25], [user:maspy,2024-06-25], [user:hos.lyric,2024-06-25]) **Honourable Mention** * 03 Slimes ([user:orzdevinwang,2024-06-25], [user:Rewinding,2024-06-25], [user:TLE,2024-06-25...
For more info about the Universal Cup and how to join the fun, visit our website at https://ucup.ac

Full text and comments »

  • Vote: I like it
  • +411
  • Vote: I do not like it

130.
Introducing Arugo — A website that provides virtual rating while practicing on problemset
By phattd, 5 years ago, In English
Introducing Arugo — A website that provides virtual rating while practicing on problemset Hello Codeforces users. Today I would like to introduce [Arugo](https://arugo.herokuapp.com/), which is a website that provides virtual rating while practicing on problemset. On this website, you can practice problems that are suggested through a suggestion system or by your custom choice. Each problem has a window of 80 minutes to solve and if you manage to solve it in time, please validate and you will earn virtual rating. However, if you gave up early or time runs out, you will lose rating eventually. Rating progress will be displayed at the homepage through a graph like in Codeforces and through it, you can visualize your progress and stay motivated to keep going. <spoiler summary="Rating progress preview"> ![Rating progress](/predownloaded/e2/88/e288e62832a048f2c01b55ec099b3e6c117a4d56.png) </spoiler> <spoiler summary="Challenge preview"> ![Challenge](/predownloaded/16/e1/16e1335d8a2b83093165ee629d45c2ea8ff65dd3.png) </spoiler> This site is inspired by my past t...
Have fun training <https://emoji.gg/emoji/8771_blobheart>

Full text and comments »

  • Vote: I like it
  • +547
  • Vote: I do not like it

131.
Codeforces Round #850 Editorial
By tourist, 4 years ago, translation, In English
Codeforces Round #850 Editorial [problem:1786A2] Problem author: [user:KAN,2023-02-15] <spoiler summary="Explanation"> [tutorial:1786A2] </spoiler> <spoiler summary="Code by KAN"> ~~~~~ NT = int(input()) for T in range(NT): n = int(input()) answer = [0, 0, 0, 0] first_card = 1 for it in range(1, 20000): who = 0 if it % 4 == 1 or it % 4 == 0 else 1 cnt = it if n < cnt: cnt = n cnt_white = (cnt + first_card % 2) // 2 cnt_black = cnt - cnt_white answer[who * 2 + 0] += cnt_white answer[who * 2 + 1] += cnt_black first_card += cnt n -= cnt if n == 0: break assert(n == 0) print(*answer) ~~~~~ </spoiler> [problem:1786B] Problem author: [user:KAN,2023-02-15] <spoiler summary="Explanation"> [tutorial:1786B] </spoiler> <spoiler summary="Code by KAN"> ~~~~~ #include <bits/stdc++.h> using namespace std; const int inf = 1000000000; int main() { int tt; cin >> tt; while (tt--) { int n, w, h; cin >> n >> w >> h; ...
~~~~~ private fun IntArray.countOf(value: Int, fun main() { repeat(readInt()) { solve() } }, private fun readLn() = readLine()!! private fun readInt() = readLn().toInt() ~~~~~, private fun solve() { val s = "win" fun IntArray.bad() = (0 until 3).singleOrNull { c

Full text and comments »

  • Vote: I like it
  • +81
  • Vote: I do not like it

132.
Where the author of the contest came up entertaining. Cheating cheaters.
By Wind_Eagle, history, 5 years ago, translation, In English
Where the author of the contest came up entertaining. Cheating cheaters. Hello, Codeforces! A month ago I have wrote [my blog about cheaters](https://codeforces.me/blog/entry/94300). Under that blog, a number of suggestions have accumulated, and there is a number of interesting ideas that could be applied to sabotage a group of cheaters. I've often seen comments along the lines of: <spoiler summary="Pictures">. <a href="https://imgbb.com/"><img src="https://i.ibb.co/r65zfTL/cheat1.png" alt="pic1" border="0"></a> <a href="https://imgbb.com/"><img src="https://i.ibb.co/Yh6ZfY8/cheat2.png" alt="pic2" border="0"></a> </spoiler> Well, doing what [user:Ari,2021-09-28] suggested wasn't really what I wanted to do, but it was worth checking out what would happen if the wrong solutions were sent. I asked some famous user what would happen if I sent the wrong solutions to cheaters. He told me that someone had done this before and that he was quickly debunked. I wondered whether I could cheat cheaters without getting caught. But for this, I had to do so...
After having a lot of fun, we decided to admit that they were just being trolled, and threw them

Full text and comments »

  • Vote: I like it
  • +526
  • Vote: I do not like it

133.
Codeforces Round #1011 (Div. 2)
By Serval, 18 months ago, In English
Codeforces Round #1011 (Div. 2) Hi Codeforces! I [user:Serval,2025-03-19] am glad to invite everyone to participate in [contest:2085], which will be held on [contest_time:2085]. This round will be rated for participants with rating lower than 2100. We will be glad to see the participants with a higher rating to take part in our round unofficially as well! You will be given 6 problems to solve in 2 hours, one of which will be divided into two subtasks. Scoring distribution will be announced later. I would like to thank everyone that makes this round possible: - [user:Error_Yuan,2025-03-19] and [user:satyam343,2025-03-19] for coordination of the round and help with the preparation. It is noteworthy that this round is the debut of [user:Error_Yuan,2025-03-19] as the coordinator. Special thanks to him! - [user:18o3,2025-03-19], [user:AG-88301,2025-03-19], [user:Dominater069,2025-03-19], [user:Edeeva,2025-03-19], [user:Graythron,2025-03-19], [user:Hanghang007,2025-03-19], [user:JagguBandar,2025-03-19], [us...
Good luck & Have fun! (∠・ω < )⌒☆

Full text and comments »

  • Vote: I like it
  • +383
  • Vote: I do not like it

134.
Codeforces Round #283: разбор (+бонусы!)
By Endagorion, 12 years ago, translation, In English
Codeforces Round #283: разбор (+бонусы!) К каждой задаче присутствует challenge &mdash; бонусная задача на тему, которую можно порешать just for fun и обсудить в комментариях. =) [problem:496A] Переберем все элементы, которые можем выкинуть, пройдем по оставшимся элементам и посчитаем максимальную разность среди соседних. Это решение имеет сложность $O(n^2)$. Можно заметить, что при удалении элемента ответ либо не поменялся, либо стал равен разности тех элементов, которые являлись соседями только что удаленного, поэтому ответ можно получить за $O(1)$, а итоговое решение будет иметь сложность $O(n)$. Ограничения позволяли сдать любое из этих решений или даже менее эффективное. **Challenge**: пусть мы удаляем не один элемент, а $k$ любых элементов (первый и последний, как и раньше, удалять нельзя). Какую минимальную максимальную разность между соседними элементами мы можем получить? Решите задачу в ограничениях $1 \leq k \leq n - 2$, $n \leq 10^5$, $a_i \leq 10^9$. [problem:496B] Заметим, что нам неважно, в каком...
for fun и обсудить в комментариях. =), tackle at the challenges for fun and practice, also feel free to discuss them at the comments. =)

Full text and comments »

  • Vote: I like it
  • +336
  • Vote: I do not like it

135.
Codeforces Round #832 (Div. 2)
By rivalq, history, 4 years ago, In English
Codeforces Round #832 (Div. 2) Hi Codeforces! I am pleased to invite you to <strike> Adhocforces</strike>, <strike> Mathforces</strike> [Codeforces Round #832 (Div. 2)](https://codeforces.me/contest/1747), which will take place on [Friday, Nov 4, 2022 at 14:35 UTC](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Codeforces+Round+832&iso=20221104T1435&p1=%3A&ah=2). You will be given **5 problems** and **2 hours** to solve them. The round will be rated for participants of Division 2 with a rating lower than **2100**. Division 1 participants can participate unofficially in the round. All problems in this round were prepared by me and [user:coderanshu,2022-11-02]. I would like to thank: - [user:antontrygubO_o,2022-11-02] for coordination of the round. - [user:ffao,2022-11-02], [user:Everule,2022-11-02], [user:Andreasyan,2022-11-02], [user:koderkushy,2022-11-02], [user:nor,2022-11-02], [user:AlperenT,2022-11-02], [user:the_hyp0cr1t3,2022-11-02], [user:Runtime-Terr0r,2022-11-02], [user:sp005,...
Good luck and have fun! See you in the standings.

Full text and comments »

  • Vote: I like it
  • +441
  • Vote: I do not like it

136.
MIT Informatics Tournament 2025-26 Winter Contest
By zhoukangyang, history, 10 months ago, In English
MIT Informatics Tournament 2025-26 Winter Contest **UPD 4:** The contest problems and editorials are available in Codeforces gym: [MITIT Winter 2025-26 Advanced Team Round](https://codeforces.me/gym/106250) [MITIT Winter 2025-26 Beginner Round](https://codeforces.me/gym/106251) [MITIT Winter 2025-26 Advanced Individual Round](https://codeforces.me/gym/106249) **Editorials:** [Team Round Editorials](https://codeforces.me/gym/106250/attachments/download/34709/MITIT_Winter_2025_2026_Team_Editorials-1.pdf). **UPD 3:** All contests have ended. Thank you all for participating! We will release the rankings and editorials soon. **UPD 2:** The team contest has officially started. You can view the [live scoreboard](https://mitit.org/Contest/ViewScoreboard/advanced-team-25-26) here. **UPD 1:** The contest has officially started. Good luck and have fun! Please join our Discord server [here](https://discord.gg/gmTUzcezv4) for the latest information! Hello Codeforces! We ( [user:ETK.,2025-11-06], [user:flame...
**UPD 1:** The contest has officially started. Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +301
  • Vote: I do not like it

137.
Codeforces Round #551 (Div. 2)
By Serval, 7 years ago, In English
Codeforces Round #551 (Div. 2) Hi Codeforces! We are glad to invite you to our first Codeforces Round [contest:1153] which will be held on [contest_time:1153]. This round will be rated for participants with rating less than 2100. We will be glad to see participants from the first division to join out of competition as well! In this round, as the best friend of Serval's, you are going to help him to solve the problems he meets. The problems are prepared by [user:bzh,2019-04-12] and me. We hope you will enjoy the round. :P Great thanks to [user:300iq,2019-04-12] for coordination of this round, [user:isaf27,2019-04-12], [user:gritukan,2019-04-12], [user:KAN,2019-04-12], [user:mohammedehab2002,2019-04-12], [user:learner99,2019-04-12], [user:aleks5d,2019-04-12] and [user:Um_nik,2019-04-13] for testing our rounds, and [user:MikeMirzayanov,2019-04-12] for the amazing Codeforces and Polygon platforms. You will be given 6 problems to solve in 2 hours. Scoring distribution will be announced later. Please ...
Good luck & Have fun! :D

Full text and comments »

  • Vote: I like it
  • +490
  • Vote: I do not like it

138.
Codeforces Round #584 (Dasha Code Championship Elimination Round) (div. 1 + div. 2)
By Errichto, 7 years ago, In English
Codeforces Round #584 (Dasha Code Championship Elimination Round) (div. 1 + div. 2) Hey, hi, hello. [contest:1209] starts on [contest_time:1209] and lasts 2h30m. The score drain will be adjusted for longer contest duration. It's a combined rated round with around eight problems. It is open and it is rated for everybody. Yes, it's rated. There are Dasha t-shirts for top 30 competitors (not counting later-to-be onsite finalists). As an extra, this is an elimination round for those who live in/near SPb/Novosibirsk. More info about the championship is in the other [blog](https://codeforces.me/blog/entry/69530). Thanks to Dasha.AI for making such an event for the community! Problems are prepared by [user:MikeMirzayanov,2019-09-14], [user:FieryPhoenix,2019-09-14], [user:dragonslayerintraining,2019-09-14] and [user:Errichto,2019-09-14]. One of these setters also created Codeforces, thanks for that! And huge thanks to [user:_kun_,2019-09-14] for coordinating the round, to [user:Merkurev,2019-09-14], [user:isaf27,2019-09-14], [user:KAN,2019-09-14] and me for test...
I wish you more fun than bugs. Enjoy the contest!

Full text and comments »

  • Vote: I like it
  • +583
  • Vote: I do not like it

139.
Fun fact about sync_with_stdio
By -is-this-fft-, history, 8 months ago, In English
Fun fact about sync_with_stdio Consider this code: ``` #include <iostream> using namespace std; int main () { ios::sync_with_stdio(false); ios::sync_with_stdio(true); } ``` In GCC, are the C++ streams like `std::cout` etc then synchronized with the corresponding C methods like `printf`? <spoiler summary="Answer"> No &mdash; the second `sync_with_stdio` has no effect at all. There is no trick here: the booleans aren't being interpreted as pointers or anything like that. There is simply no code to handle turning synchronization back on. <spoiler summary="Implementation of sync_with_stdio"> ``` bool ios_base::sync_with_stdio(bool __sync) { // _GLIBCXX_RESOLVE_LIB_DEFECTS // 49. Underspecification of ios_base::sync_with_stdio bool __ret = ios_base::Init::_S_synced_with_stdio; // Turn off sync with C FILE* for cin, cout, cerr, clog iff // currently synchronized. if (!__sync && __ret) { // Make sure the standard streams are constructed. i...
Fun fact about sync_with_stdio

Full text and comments »

  • Vote: I like it
  • +203
  • Vote: I do not like it

140.
Codeforces Round 1051 (Div. 2)
By LucaLucaM, 12 months ago, In English
Codeforces Round 1051 (Div. 2) Hello, Codeforces! Or, as we like to say in Romania: *Poți să îmi dai link la rundă în privat să testez?* We are proud to invite you to [contest:2143], which will be held on [contest_time:2143]. The round will be rated for participants whose rating is **below 2100**, but higher rated users are also welcome to participate out of competition. You will be given **6-7 problems**, one of which will be divided into a subtask, and **2 hours** to solve them. The problems were authored by [user:anpaio,2025-09-15], [user:tvladm,2025-09-15], [user:MateiKing80,2025-09-15] and by yours truly. We would like to thank: - [user:ntherner,2025-07-07] and [user:Vladithur,2025-07-07] for coordinating the round, - ~rolandpetrean,2025-09-15 ~waipoli,2025-09-15 ~Turcavid,2025-09-15 ~tibinyte2006,2025-09-15 ~_istil,2025-09-15 ~Tudy006,2025-09-15 ~mircea_007,2025-09-15 ~madlogic,2025-09-15 ~Non-origination,2025-09-15 ~AlanSkarica,2025-09-15 ~ToniB,2025-09-15 ~andrei_C1,2025-09-15 ~AleXutzZu...
Good luck & have fun!

Full text and comments »

  • Vote: I like it
  • +405
  • Vote: I do not like it

141.
Unofficial Editorial for Educational Round 94 (Div. 2)
By neal, 6 years ago, In English
Unofficial Editorial for Educational Round 94 (Div. 2) Haven't done one of these for a while! Here are my approaches to the problems: #### [problem:1400A] We just need to make sure our string of $n$ characters matches each of the $n$ substrings in at least one spot. The easiest way to do this is to take every other character from $s$. Code: [submission:90908018] Another fun solution: we can generate random strings and check them until we find one that matches everything. This works because the probability of failing to match any particular substring is $\frac{1}{2^n}$, so as $n$ gets bigger the probability of failing gets extremely low. Code: [submission:90999219] #### [problem:1400B] First iterate on the number of swords we will personally take. Then we should greedily take as many war axes as we can until we run out of money. At this point, our follower needs to take as many items as possible. They can do this by greedily taking whichever of swords or war axes are cheaper until they run out, followed by taking the more expensi...
Another fun solution: we can generate random strings and check them until we find one that matches

Full text and comments »

  • Vote: I like it
  • +416
  • Vote: I do not like it

142.
VK Cup 2016 — Round 1
By Radewoosh, history, 10 years ago, In English
VK Cup 2016 — Round 1 <img src="http://cdn.icmgworld.com/architectureawards/2014/images/awards/Round_1.png" style="float:left; margin:0 1em 1em 0"/> Hello everybody! I'm glad to announce that Round 1 of VK Cup 2016 will take place this Monday, and me ([user:Stonefeang,2016-03-26]) and Kamil Dębowski ([user:Errichto,2016-03-26]) are the problemsetters! There will be an official round for teams from VK cup, but if you are not eligible to participate in it, then you can compete (alone, not in team) in one of two additional editions (one for div.1 and one for div.2), so everybody is invited to take part in the competition! Just register in your category [here](http://codeforces.me/contests/639,657,658). All three rounds will be **rated**. Div.1 and Div.2 editions will look like normal CF round, but will have common problems with official edition. If you can't register before the round, then you will be able to do it during the contest (but not for the entire duration, you can cheсk it [here](http:/...
We wish you good luck and great fun! Can't wait to see you during the contest! :D

Full text and comments »

Announcement of VK Cup 2016 - Round 1
  • Vote: I like it
  • +364
  • Vote: I do not like it

143.
Codeforces Round #821 (Div. 2)
By 055D, 6 years ago, In English
Codeforces Round #821 (Div. 2) Hello Codeforces! We invite you to [contest:1733] starting on [contest_time:1733]. The round is **rated for users whose rating is lower than 2100**. All problems were mainly created and prepared by me. One problem is revised by [user:mejiamejia,2022-09-17]. I would also like to thank: - [user:MikeMirzayanov,2022-03-01] for Codeforces and Polygon platforms, - [user:KAN,2022-09-09] for helping preparation of the round, - [user:Arpa,2022-03-01] for coordinating and reviewing the round, - [user:mejiamejia, 2022-09-17] for developing one problem and a lot of advices, - [user:satyam_343,2022-07-09], [user:74TrAkToR,2022-07-12], [user:MagentaCobra,2022-07-27], [user:cadmiumky,2022-08-05], [user:Andreasyan,2022-08-05], [user:darkkcyan,2022-08-06], [user:Vladithur,2022-08-09], [user:Etherite,2022-08-10], [user:welleyth,2022-08-17], [user:mjhmjh1104,2022-08-27], [user:emorgan5289,2022-09-18], [user:jeroenodb,2022-09-18], [user:oolimry,2022-09-18], [user:willy108,2022-09-18], [user:...
Good luck, and have fun!

Full text and comments »

  • Vote: I like it
  • +404
  • Vote: I do not like it

144.
MIT Mystery Hunt
By Um_nik, history, 4 years ago, In English
MIT Mystery Hunt Disclaimer: This blog is not about competitive programming; you probably will not learn anything about algorithms and data structures. In other words, it doesn't qualify for [this initiative](https://codeforces.me/blog/entry/110840), but I want to give a link to it anyways because I think it's cool. I love solving problems. No, seriously. I LOVE it. The mindset described in [this blog](https://codeforces.me/blog/entry/91114) is 100% how I feel. But it is not constrained to competitive programming problems. I loved math problems for a much longer time, and physics was somewhere there. But I also love solving puzzles. And playing puzzle games on the computer (well, on consoles). And participating in intellectual games. I am not as good in them as in cp, but it was never about being good for me, I just love the process. And I think that there might be some people with a similar love for puzzles among competitive programmers, this is why I decided to write this blog on CF <s>and no...
](https://interestingthings.museum/) ended yesterday, and this weekend was one of the mostfun

Full text and comments »

  • Vote: I like it
  • +356
  • Vote: I do not like it

145.
Background of Good Bye 2019
By antontrygubO_o, 7 years ago, In English
Background of Good Bye 2019 Hi there! The recent Good Bye 2019 was very important event for us, and thanks for all the positive feedback we got, especially from [user:Radewoosh,2020-01-01]! As a follow-up, we would like to share some background on its preparation. ### **Problems:** **A**: This one was the hardest to come up with. We wanted it to be super easy but still to include some idea, and this is like the $10$th version of the problem. **B**: Initially there was another problem at this position. However, it turned out to be too hard for B (one orange couldn’t do it during the testing), and people didn’t like it in general, so we came up with another task. **C**: Funny, but we didn’t know that it’s always possible to make array good with adding at most $1$ element before the contest. **D**: This problem was created just 3 days before the contest to make it more balanced :O. We are glad that the contest did turn out to be well-balanced. **E**: Initially we wanted this problem to be at positi...
Fun fact: initially we considered G and H to be of about the same difficulty. The contest proved

Full text and comments »

  • Vote: I like it
  • +374
  • Vote: I do not like it

146.
Codeforces Round #628 (Div.2)
By mohammedehab2002, history, 6 years ago, In English
Codeforces Round #628 (Div.2) Hi! Codeforces round #628 (vintage Codeforces round #2) will take place on [contest_time:1325]. It's rated for the second division, but, as usual, first division participants can take part out of competition. The problems were created by me. I'd like to thank, and orz, [user:antontrygubO_o,2020-03-12] for coordinating the round; [user:ramchandra,2020-03-12], [user:pajenegod,2020-03-12], [user:aryanc403,2020-03-12], [user:Taran_1407,2020-03-12], [user:Kuroni,2020-03-12], [user:mcdx9524,2020-03-12], [user:dorijanlendvaj,2020-03-12], [user:Andreasyan,2020-03-12], [user:300iq,2020-03-12], [user:zoooma13,2020-03-12], [user:Osama_Alkhodairy,2020-03-12], [user:Mohammad_Yasser,2020-03-14], and [user:DeadPillow,2020-03-12] (special shout-out) for testing the round; and of course [user:MikeMirzayanov,2020-03-12] for the great codeforces and polygon platforms. You'll be given 6 problems and 2 hours to solve them. **UPD:** the scoring distribution will be 500-750-1250-1750-2500-2750. ...
Good luck & Have fun!

Full text and comments »

  • Vote: I like it
  • +671
  • Vote: I do not like it

147.
Pinely Round 3 (Div. 1 + Div. 2)
By TheScrasse, 3 years ago, In English
Pinely Round 3 (Div. 1 + Div. 2) <img src="https://assets.codeforces.com/images/pinely_logo.png" align="right" style="height: 200px;" alt="text"/> Ciao, Codeforces! We're glad to invite you to take part in [contest:1909], which will start on [contest_time:1909]. You will be given **9 problems** and **3 hours** to solve them. One of the problems will be divided into two subtasks. The problems were authored and prepared by me. <spoiler summary="Spoiler"> ![ ](https://i.imgur.com/lipiKQE.png) </spoiler> We would like to thank - [user:errorgorn,2023-12-20] for his fun &#129292; &#x1F921; &#x1F913; &#x1F629; coordination; - [user:Alexdat2000,2023-12-20] for Russian translation; - [user:franv,2023-12-20] for writing $173$ lines of checker of problem H correctly at the first try; - [user:franv,2023-12-20] for pictures in the editorial; - [user:dario2994,2023-12-20], [user:Endagorion,2023-12-20], [user:ffao,2023-12-20], [user:Golovanov399,2023-12-20], [user:nor,2023-12-20] for VIP testing; - [user:Kaey,202...
- [user:errorgorn,2023-12-20] for his fun 🤌 🤡 🤓 😩 coordination

Full text and comments »

  • Vote: I like it
  • +797
  • Vote: I do not like it

148.
Codeforces Round #853 (Div. 2)
By Serval, history, 4 years ago, In English
Codeforces Round #853 (Div. 2) **UPD: The start time has been changed. Note that the start time is unusual.** Hi Codeforces! [user:Bazoka13,2023-02-23], [user:Toxel,2023-02-23], and I [user:Serval,2023-02-23] are glad to invite everyone to participate in [contest:1789], which will be held on [contest_time:1789]. This round will be rated for participants with rating lower than 2100. We will be glad to see the participants with a higher rating to take part in our round unofficially as well! You will be given 6 problems to solve in 2 hours. Scoring distribution will be announced later. We would like to thank everyone that makes this round possible: - [user:Artyom123,2023-02-23] for coordination of the round and help with the preparation. - [user:SSerxhs,2023-02-23], [user:skywalkert,2023-02-23], [user:zlc1114,2023-02-23], [user:foreverlasting,2023-02-23], [user:tiger2005,2023-02-23], [user:OMG_link,2023-02-23], [user:fried-chicken,2023-02-23], [user:tibinyte,2023-02-23], [user:_Viole_,2023-02-23], [u...
Good luck & Have fun! :P

Full text and comments »

  • Vote: I like it
  • +394
  • Vote: I do not like it

149.
Codeforces Round #462
By Tommyr7, history, 9 years ago, In English
Codeforces Round #462 Hi, Codeforces! Happy Valentine's Day. And happy Lunar New Year! I'm quite honored to invite you to Codeforces Round #462 which will take place at [15:05 MSK on 14 Feb](https://www.timeanddate.com/worldclock/fixedtime.html?day=14&month=2&year=2018&hour=15&min=5&sec=0&p1=166) and last for two hours. The authors are [user:quailty,2018-02-12], [user:skywalkert,2018-02-12], [user:visitWorld,2018-02-12] and me. This is our second round here. The round couldn't have been realized without efforts of [user:KAN,2018-02-12] and our testers: [user:cyand1317,2018-02-12], [user:demon1999,2018-02-12]. Thanks for your help to the contest. Also, thank [user:MikeMirzayanov,2018-02-12] for the fantastic Codeforces and Polygon platforms. The contest will consist of five problems and it is **rated** for both division contestants. The background of problems will be about Lunar New Year. (Yes... Not Valentine's Day...) Hope to see you in the contest! Good luck and have fun, wish you a hig...
Hope to see you in the contest! Good luck and have fun, wish you a high rating!

Full text and comments »

  • Vote: I like it
  • +544
  • Vote: I do not like it

150.
Editorial for Codeforces Round #761 (Div. 2)
By snowysecret, 5 years ago, In English
Editorial for Codeforces Round #761 (Div. 2) Thanks for participating, hope you enjoyed the problems! Implementations for the problems are chosen randomly among testers, and I made some changes to their codes (for example, deleted meaningless comment lines). Please do not hesitate to provide feedback in the comments, so I can improve in setting problems next time. **UPD**: Sorry but there is a checker bug in problem E. All submissions of problem E will be rejudged soon. **UPD2:** Rejudge done, the round remains rated. <spoiler summary="Statistics"> Number of FST for rated participants: - Problem A: $29$ - Problem B: $90$ - Problem C: $12$ - Problem D1: $4$ - Problem D2: $0$ - Problem E: $6$ Number of AK: $22$ Number of clarifications: $85$ </spoiler> [problem:1617A] <spoiler summary="Hint"> When is the lexicographically smallest permutation of $S$ (i.e. the sorted string) not the answer? </spoiler> <spoiler summary="Solution"> If there are no occurrences of `a`, `b` or `c` in $S$, ...
Originally, the author and two testers' solutions are all wrong, but

Full text and comments »

  • Vote: I like it
  • +425
  • Vote: I do not like it

151.
Codeforces Round 1046 (Div. 1, Div. 2)
By Register, 12 months ago, In English
Codeforces Round 1046 (Div. 1, Div. 2) Hello, Codeforces! We, the RiOI team, are proud to invite you to participate in [contest:2135] and [contest:2136] which will be held on [contest_time:2135]. The round will be **rated for everyone**. You will be given **6 problems** in both divisions, where some problems will be divided into subtasks, and **3 hours** to solve them. For both divisions, the number of interactive problems will **not be equal to 1**, so you may need to read the [guide for interactive problems](https://codeforces.me/blog/entry/45307) before the contest. The problems are authored and prepared by [user:Register,2025-08-24], [user:STUDENT0,2025-08-24], [user:Error_yuan,2025-08-24], [user:_istil,2025-08-24], and [user:Alan_dong,2025-08-24]. We would like to thank: - [user:Error_Yuan,2025-08-24] for his great coordination. - [user:Alexdat2000,2025-08-24] for Russian translation. - [user:Um_nik,2025-08-24], [user:errorgorn,2025-08-24], [user:SSerxhs,2025-08-24], [user:dorijanlendvaj,2025-08-24] a...
Good luck & Have fun! (∠・ω < )⌒☆

Full text and comments »

  • Vote: I like it
  • +381
  • Vote: I do not like it

152.
Codeforces Round 1118 (Div. 2)
By ItsNotMeItsYou, 9 days ago, In English
Codeforces Round 1118 (Div. 2) # Merhaba Codeforces! We are proud to invite you to [contest:2258], which will be held on [contest_time:2258]. The round will be rated for participants whose rating is **below 2100**, but higher rated users are also welcome to participate out of competition. You will be given **6 problems**, one of which will be divided into a subtask, and **2 hours** to solve them. Also, there is **at least one** interactive problem, so you are recommended to read the [guide](https://codeforces.me/blog/entry/45307) to interactive problems if you have not encountered them before. The problems were authored by me ([user: ItsNotMeItsYou,2025-10-31]), [user:carcinisation,2025-11-17], [user:mychecksdead,2025-11-24] and [user:Seferoglu,2024-06-07]. This round was prepared by some members of the 2025 and 2026 IOI team of Türkiye, and we hope you enjoy all our problems. We would like to thank: - [user:cadmiumky,2023-11-08] for his outstanding coordination of the round, - [user:um_nik,...
Good luck & have fun!

Full text and comments »

  • Vote: I like it
  • +318
  • Vote: I do not like it

153.
Codeforces Round #326
By PrinceOfPersia, history, 11 years ago, In English
Codeforces Round #326 Hello Codeforces. I'm honored to announce you, that Codeforces round #326 is gonna take place [soon](http://timeanddate.com/worldclock/fixedtime.html?day=15&month=10&year=2015&hour=19&min=30&sec=0&p1=166) on Codeforces. Writers are AmirMohammad Dehghan([user:PrinceOfPersia,2015-10-01]) and Ali Haghani([user:Haghani,2015-10-08]). There will be 6 problems in each division(4 problems are common) and you'll have 2 and a half hour to solve them. I hope you enjoy the problems. I wanna thank Maxim Akhmedov([user:Zlobober,2015-10-01]) for his great helps in preparing this round, [user:MikeMirzayanov,2015-10-01] for wonderful platforms of Codeforce and Polygon, [user:Delinur,2015-10-08] for translating problem statements into Russian and MohammadReza Maleki([user:mruxim,2015-10-13]) and Ali Bahjati([user:AliB,2015-10-13]) for their great advices (and [user:AliB,2015-10-13] again for some graphics). This is my third round on Codeforces and not the last one, I hope. This is the las...
working with him. We had a lot of fun and interesting contests during his coordination. I just wanna

Full text and comments »

  • Vote: I like it
  • +721
  • Vote: I do not like it

154.
Unbelieveable story of success at ACM ICPC final
By Bredor, history, 10 years ago, translation, In English
Unbelieveable story of success at ACM ICPC final Preparing to contest ==================== For long time I haven't been writing stories about my life. As Nietzsche said &mdash; Bredor died, and I don't feel so good myself. You might be thinking that I went into booze. Actually, I have really been drinking so much all this time, but I had more important activities: once upon a time I came to my college to find a company to drink. There I saw an advertisment about programming competitions, but I found that competitive programming is sense less in school and it didn't attract my attention. Soon, I was summoned to the dean, and the dean told me: "mr. Rudolph Gotov, there is noone except you who can win this contest!". I refused him at first time certainly, but then he offered me hard choices such as to continue winning all contests or to stop to arrange night parties at college campus. The choice was not great, and I went looking for a team. Because of stupid rules I could not invite my friends from Bratsk into the team, so I had t...
It was a short prelude, and now I would describe how we had fun in Phuket mor detaily, (in reason

Full text and comments »

  • Vote: I like it
  • +625
  • Vote: I do not like it

155.
Codeforces Round #716 (Div.2)
By mohammedehab2002, 5 years ago, In English
Codeforces Round #716 (Div.2) Hi everyone! Codeforces round #716 will take place on [contest_time:1514]. It's rated for the second division, but, as usual, first division participants can take part out of competition. The problems are based on the Egyptian IOI qualification, and they were created by me and [user:mahmoudbadawy,2021-04-17]. I'd like to thank: - [user:KAN,2021-04-17] and [user:Nebuchadnezzar,2021-04-17] for their excellent coordination. - [user:antontrygubO_o,2021-04-17] for improving a problem, then rejecting all our problems without reading them, then testing the round. - [user:Yousef_Salama,2021-04-17], [user:Mohammad_Yasser,2021-04-17], [user:Noureldin,2021-04-17], and [user:Commando_,2021-04-17] for testing the official contest. - [user:74TrAkToR,2021-04-17] and [user:psevdoinsaf,2021-04-17] for testing the round. - [user:MikeMirzayanov,2021-04-17] for the great codeforces and polygon platforms. This may be the most and only balanced round I've ever set. You'll be given 5 problems...
Good luck & Have fun :D

Full text and comments »

  • Vote: I like it
  • +639
  • Vote: I do not like it

156.
fix problem ratings pls (the rainboy effect)
By galen_colin, 2 years ago, In English
fix problem ratings pls (the rainboy effect) [The first few paragraphs of this blog, above the first spoiler, are just for story purposes and are irrelevant to the problem statement] One fateful day, a naive and young version of me from about 5 days ago had a dream. A dream to stop being so terrified of hard problems. A dream to conquer the most challenging stuff that CF ever had to offer. A dream to... ok, enough of that, that's so stupid. Basically, I've been grinding 3500s lately, mostly for fun (and my god, has it been fun). Two days prior, I found myself solving [1919G](https://codeforces.me/contest/1919/problem/G). That went fine, but after getting it, I noticed that despite G being 3500, it wasn't even the hardest problem in the contest &mdash; that honor went to the next problem, [1919H](https://codeforces.me/contest/1919/problem/H) (the subject of this blog), which had **no solves in-contest**. I concluded that I would have to be insane to try that, and moved on to other problems. Well, yesterday, I decided I...
incredibly fun and takes most of the stress away from practice (no worries about what you *should* be, lately, mostly for fun (and my god, has it been fun)., Basically, they very quickly stopped being fun. Not to say that *problem solving* has stopped being

Full text and comments »

  • Vote: I like it
  • +360
  • Vote: I do not like it

157.
Codeforces Round #717 (Div.2)
By mohammedehab2002, 5 years ago, In English
Codeforces Round #717 (Div.2) It's me again! Codeforces round #717 will take place on [contest_time:1516], an hour early than the usual timing. It's rated for the second division, but, as usual, first division participants can take part out of competition. The problems were created by me, and some of them are based on the Egyptian IOI qualification. I'd like to thank: - [user:KAN,2021-04-19] and [user:Aleks5d,2021-04-19] for their excellent coordination. - [user:Akulyat,2021-04-19], [user:__cucumber__,2021-04-19], [user:Randle,2021-04-19], [user:Riladavin,2021-04-19], [user:Waley,2021-04-19], [user:MForest,2021-04-19], [user:_Stefan_,2021-04-19], [user:RabbitPower,2021-04-19], and the official contestants, I guess, for testing the round. - [user:MikeMirzayanov,2021-04-19] for the great Codeforces and Polygon platforms. You'll be given 5 problems, but this time you'll have 2 hours to solve them. **UPD:** the scoring distribution will be 500-1000-1500-2000-2750. **UPD:** [the editorial.](https://c...
Good luck & Have fun :D

Full text and comments »

  • Vote: I like it
  • +637
  • Vote: I do not like it

158.
Codeforces Round #318 [RussianCodeCup Thanks-Round]
By Errichto, 11 years ago, In English
Codeforces Round #318 [RussianCodeCup Thanks-Round] Hello Codeforces community! Codeforces Round #318 (for both divisions) will take place on [August, 29 at 19:30 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?day=29&month=8&year=2015&hour=19&min=30&sec=0&p1=166). It is the Thanks-Round devoted to Russian Code Cup. You will be given 5 problems and 2 hours to solve them. Scoring will be announced close to the round. I strongly recommend you to read all problems. ![ ](http://codeforces.me/predownloaded/97/f0/97f0ed2e07a03e20ded192532c533b620734da64.jpg) <a href="http://www.russiancodecup.ru/">RussianCodeCup</a> is the largest open programming competiton for Russian-speaking participants by Mail.Ru Group. Its history started in 2011. And since the first championship RCC offers great problems and generous prizes. This year finals will be held on September, 19th. Wish good luck to all the finalists! Thank you, RussianCodeCup, for your gift on the 5th anniversary of Codeforces! I am honoured to be a problem setter ...
I wish you great fun and no frustrating bugs. Looking forward to seeing you!

Full text and comments »

  • Vote: I like it
  • +380
  • Vote: I do not like it

159.
Codeforces Round 1105 (Div. 1, Div. 2)
By Gold14526, history, 2 months ago, In English
Codeforces Round 1105 (Div. 1, Div. 2) #### 你好，Codeforces! We are delighted to invite you to participate in [contest:2239] or [contest:2240], both of which will be held on [contest_time:2239]. For both division 1 and division 2, you will be given **$2.5$ hours** to solve **$6$ problems** in each division. The problems were authored and prepared by [user:Gold14526,2026-06-22], [user:Milkcat2009,2026-06-22] and [user:wangmarui,2026-06-22]. We would really like to thank the following people for making this round possible: - ~Um_nik,2026-06-26 for the preliminary review of the round - [user:cadmiumky,2026-06-22] for the great coordination. - ~Alexdat2000,2026-06-29 for providing Russian translations. - [user:hcywoi,2026-06-22] and [user:Network_Error,2026-06-22] who also prepared problems that were ultimately not used in this round. - [user:lkrqwq,2026-06-22] for optimizing many details of problems. - [user:Starsilk,2026-06-23] and [user:errorgorn,2026-06-22] for black red testing. - [user:Network_Error,202...
Good Luck & Have Fun!

Full text and comments »

  • Vote: I like it
  • +346
  • Vote: I do not like it

160.
ICPC World Finals in Astana: I invite you to a push-up challenge!
By MikeMirzayanov, 2 years ago, In English
ICPC World Finals in Astana: I invite you to a push-up challenge! Hi everyone! At the ICPC World Finals in Astana, there's an Alumni Zone, and I've been invited there on [September 18th from 16:30 to 17:00](https://www.timeanddate.com/worldclock/fixedtime.html?msg=ICPC+World+Finals+in+Astana%3A+push-up+challenge&iso=20240918T1630&p1=921&am=30) (Astana time/UTC+5). I suggest we hold a push-up challenge during this time! I'm ready to participate and would be happy to see other participants. Let's do some push-ups! Are you ready? I'll give a Codeforces t-shirt to the winner. If this isn't your kind of sport and you're only into competitive programming, feel free to drop by to cheer and have fun. See you there! **UPD 1:** Thanks to [user:1.6,2024-09-16] for the idea! I'm planning to stream (instagram live) from my Instagram account: https://www.instagram.com/mikemirzayanov/ **UPD 2:** People came up to me and asked about the format. I think we'll do it this way: we'll do sets of 25 push-ups. Gradually, people will start dropping out. Wh...
competitive programming, feel free to drop by to cheer and have fun.

Full text and comments »

  • Vote: I like it
  • +787
  • Vote: I do not like it

161.
Codeforces Round 1086 (Div. 2)
By Mindeveloped, history, 6 months ago, In English
Codeforces Round 1086 (Div. 2) Hello, Codeforces! [user:abc864197532,2026-03-09] and I are pleased to invite you to [contest:2208] on [contest_time:2208]! You will be given $5$ problems to solve in $2$ hours. Some of these problems are divided into subtasks. The scoring distribution is $500-1000-1250-(1250+1250)-3000$. The problems of this round were prepared by [user:tybbs,2026-03-09], [user:Mini_PEKKA,2026-03-09] and me. We would like to thank the following people for making this round possible. - [user:abc864197532,2026-03-09] for his wonderful coordination. - [user:Alexdat2000,2026-03-09] for Russian translation. - [user:__baozii__,2026-03-09], [user:_istil,2026-03-09], [user:ETO_leader,2026-03-09], [user:Fysty,2026-03-09], [user:Wiwiho,2026-03-09], [user:amano_hina,2026-03-09], [user:baluteshih,2026-03-09] and [user:max0810,2026-03-09] for red testing. - [user:Friedrich,2026-03-09], [user:Halberd_Cease,2026-03-09] and [user:guagua0407,2026-03-09] for orange testing. - [user:CSQ31,2026-03-09], ...
Good luck & Have fun!

Full text and comments »

  • Vote: I like it
  • +278
  • Vote: I do not like it

162.
Codeforces Round 1004 (Div. 1, Div. 2)
By sevlll777, 19 months ago, In English
Codeforces Round 1004 (Div. 1, Div. 2) Hello again, Codeforces! I am glad to invite you to [contest:2066], [contest:2067], at [contest_time:2066]. In Division 1 you will be offered $6$ problems. In Division 2 you will be offered $7$ problems. One of the problems in Div.1 will be divided into 2 subtasks. Round duration is set to be **2 hours**. Also, both divisions contain _at least one_ interactive problem(s), so be prepared for those! [Guide for interactive problems](https://codeforces.me/blog/entry/45307) I would like to thank, - [user:FairyWinx,2025-02-09] for dedicated coordination, a lot of problemset discussion, and suggesting one of the problems idea. - Our testers: [user:Dart-Xeyter,2025-02-09], [user:I_love_kirill22,2025-02-09], [user:RP-1,2025-02-09], [user:larush,2025-02-09], [user:Wansur,2025-02-09], [user:furt1ve,2025-02-09], [user:Iura_Shch,2025-02-09], [user:SomethingNew,2025-02-09], [user:Gabbasov,2025-02-09], [user:glllll,2025-02-09], [user:domovonok,2025-02-09], [user:Error_Yuan,2025-02...
As always, we hope you will like the problems. Have fun!

Full text and comments »

  • Vote: I like it
  • +294
  • Vote: I do not like it

163.
Codeforces Round #190
By cgy4ever, 13 years ago, In English
Codeforces Round #190 Hello, everyone! Do you want to train your skill by a contest before [ACM/ICPC Finals](http://icpc.baylor.edu/worldfinals)? Codeforces Round #190 will take place on [Friday, June 28th at 19:30 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?msg=Codeforces+Round+%23190&iso=20130628T1930&p1=166&ah=2). This is the last chance to practice, don't miss it! I am [user:cgy4ever,2013-06-26] from China, and this is my first round on Codeforces, I hope you will love it. As usual, there will be 7 problems: 2 for Div2, 2 for Div1 and 3 for both. I am the writer of them. And I would like to thank [user:Gerald,2013-06-26] and [user:sdya,2013-06-26] for testing, and [user:MikeMirzayanov,2013-06-26] for the Codeforces project including [polygon](http://codecenter.sgu.ru/polygon/home) system. Good luck and have fun! **Update 1**: The score distribution for Both Division is regular (500-1000-1500-2000-2500). The main character of all problem will be: Fox Ciel. (See [here](http...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +347
  • Vote: I do not like it

164.
Codeforces Round 1083 (Div. 2)
By Leftist_G, 6 months ago, In English
Codeforces Round 1083 (Div. 2) #### 你好, Codeforces! <img src="/predownloaded/ee/40/ee40e93b2b5e01607ec07e0bea1ff7d7c2dadfaf.png" style="width: 300.0px;float: right;margin: 0 1.0em 1.0em 1.0em;max-width: 100.0%;max-height: 100.0%;"> We (DBOI Team) are very glad to invite you to participate in [contest:2205], starting at [contest_time:2205]. There will be **7 problems** for you to solve in **2 hours and 30 minutes**. All problems were authored and prepared by [user:cool_milo,2026-02-19], [user:StayAlone,2026-02-19] and me. This round will be rated for all participants with **rating below 2100**. I would like to thank the following list of very strong individuals for making this round possible: - [user:Error_Yuan,2026-02-19] for the excellent coordination and for making problems better. - [user:Alexdat2000,2026-02-19] for Russian translation. - [user:CTHOOH,2026-02-19], [user:LiHn,2026-02-19], [user:Angelic717,2026-02-19], [user:StayAlone,2026-02-19] and me for providing some rejected problems. - All ...
Good Luck & Have Fun!

Full text and comments »

  • Vote: I like it
  • +377
  • Vote: I do not like it

165.
[Tutorial] Common Mistakes in Competitive Programming and How to Avoid Them
By YouKn0wWho, 4 years ago, In English
[Tutorial] Common Mistakes in Competitive Programming and How to Avoid Them One thing is for sure. You do make mistakes. I also make miskates and that's what makes us human. But what we can surely do is &mdash; to try to minimize the errors that we make throughout our life. I have compiled some of the mistakes that I made in my early Competitive Programming phase. I also mentioned how to avoid them. Also, in most cases, I will give you a chance to find out what the bug is before I reveal the culprit as I tried to make this blog interactive. The codes that I have used in this blog have been written in C++ as it is the most used language for CP. **So, if you are new to CP, stick with me as you might don't wanna repeat the mistakes that I made when I was a beginner.** #### Mistake 1 Check out the following code: <spoiler summary="Code"> ~~~~~ #include<bits/stdc++.h> using namespace std; int main() { int a = 1000'000'000,b = 1000'000'000; long long product = a * b; cout << product << '\n'; return 0; } ~~~~~ </spoiler> The outp...
most of the fun. The rest is seeing practice paying off every once in a while. If everyone could have

Full text and comments »

  • Vote: I like it
  • +634
  • Vote: I do not like it

166.
Making NTT convolution 10x faster with avx2
By Qwerty1232, 17 months ago, In English
Making NTT convolution 10x faster with avx2 > Text is also available on [github pages](https://piskareviv.github.io/blog_aux_ntt_1/) (formatting may look a bit cleaner there) > Thanks [user:alexxela12345,2025-05-05] for reviewing this blog Hello everyone! I want to share some of my thoughts and experiments on vectorizing NTT. I prefer NTT to real-valued FFT because of the imprecision of the latter. I use `avx2` because it is the most advanced vector extension supported by the majority of modern online judges (including Codeforces), as of 2024. And I have no idea how many bugs (already found two) and how much UB my code contains, at least it passes some kind of tests. ### Benchmark info All the benchmarks are performed on my `Ubuntu 22` `Intel i5-1135g7` laptop. I execute `cpupower frequency-set -d 3.0ghz -u 3.0ghz` before benchmarks to (attempt to) fix CPU frequency for better accuracy. Code is available at [github](https://github.com/piskareviv/blog_aux_ntt_1). You can try running all the benchmarks o...

Full text and comments »

  • Vote: I like it
  • +366
  • Vote: I do not like it

167.
Codeforces Round 1081 (Div. 2)
By Jamshed11, 7 months ago, In English
Codeforces Round 1081 (Div. 2) Hello Codeforces !!! I am very excited to invite you to participate in [Codeforces Round 1081](https://codeforces.me/contests/2192), which will be held on [contest_time:2192]! You will be given **$\mathbf{2}$ hours** to solve **$\mathbf{6}$ problems**. This round will be rated for all participants with **rating below 2100**. This is my first time hosting an official Codeforces round, and all the problems are authored by me. I hope you will enjoy the round. This round would not be possible without the help of the following people: - [user:Proof_by_QED,2026-02-18] for excellent coordination and improving the problems. - [user:flamestorm,2026-02-18] and [user:ScarletS,2026-02-18] for initial coordination of the round. - [user:Alexdat2000,2026-02-18] for russian statement translation. - All the testers for testing and sharing valuable feedback: [user:__baozii__,2026-02-18], [user:YuukiS,2026-02-18], [user:N_z__,2026-02-18], [user:sammyuri,2026-02-18], [user:Ari,2026-02-18],...
Good Luck & Have Fun !

Full text and comments »

  • Vote: I like it
  • +362
  • Vote: I do not like it

168.
Codeforces Round #282
By matrix, 12 years ago, In English
Codeforces Round #282 Hi, Codeforces Round #282 will be held at [13th of December, 19:30 MSK](http://timeanddate.com/worldclock/fixedtime.html?day=13&month=12&year=2014&hour=19&min=30&sec=0&p1=166). Please don't note anything since the time is the usual time of contests. The round is prepared by [user:FarbodY,2014-12-12], [user:Haghani,2014-12-12] and Me([user:matrix,2014-12-12]). We'd like to thank [user:Zlobober,2014-12-12] who helped us a LOT for preparing the problems, [user:MikeMirzayanov,2014-12-12] for the Polygon and Codeforces platforms and [user:delinur,2014-12-13] for helping us in preparing statements and translating them. Our special thanks goes to [user:mruxim,2014-12-12] for testing the round. The problems will be sorted according to the estimated order of difficulty according to our opinion but we strongly recommend you to read all of the problems. As always the update regarding score distribution will be posted **just** before the round starts. :) **UPD**: It was writ...
Good luck and Have fun!

Full text and comments »

  • Vote: I like it
  • +383
  • Vote: I do not like it

169.
Creating Gravity Defied tracks using Codeforces rating graph
By awoo, history, 11 years ago, translation, In English
Creating Gravity Defied tracks using Codeforces rating graph Introduction ============ <img src="http://cs624422.vk.me/v624422694/36ac0/8jKq7pMzPOc.jpg" style="float: right;"></img> Hi everybody! Recently I have decided to refresh memories about good old times and play Gravity Defied on my phone. It wasn't really hard to find port of that legendary game from J2ME to modern platforms. It rapidly gained glory among students of past decade. Key points of Gravity Defied success were nice gameplay (biker completing different stages with high cliffs and deep pits), convinient physics (ability to rotate mid-air) and simplicity of modmaking. As for me, it was a bit more than usual game. When I had completed over thousand tracks, I began earning money on helping others to progress. Only later even more difficult games were developed: HOMM 3, Far Cry and Dark Souls... Predevel story ============ <img src="http://cs624422.vk.me/v624422694/370dd/wU1hi77t6U8.jpg" style="float: right;"></img> And now Gravity Defied is on my phone again! Not o...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +245
  • Vote: I do not like it

170.
Codeforces Round #616 Editorial
By Kuroni, history, 7 years ago, In English
Codeforces Round #616 Editorial Hello everyone, this is the editorial for [contest:1290] and [contest:1291]! Along with the solution to each problem, we will have the theme and easter egg solution as well! I hope you all enjoyed our problems ( ´ ▽ ` )b [problem:1291A] Author: [user:265918,2020-02-02] <spoiler summary="Tutorial"> [tutorial:1291A] </spoiler> <spoiler summary="Implementation"> ~~~~~ #include <bits/stdc++.h> using namespace std; int main() { ios::sync_with_stdio(false); cin.tie(nullptr); int t; cin >> t; while (t--) { int n; cin >> n; string s; cin >> s; int odd = 0; for (char c : s) if ((c - '0') & 1) odd++; if (odd <= 1) { cout << "-1\n"; continue; } int cnt = 0; for (char c : s) { if ((c - '0') & 1) { cout << c; cnt++; } if (cnt == 2) break; } cout << '\n'; } return 0; } ~~~~~ </spoiler> [problem:1291B] Author: [user:hugopm,2020-02-02...
Hope you have fun with the easter eggs we provided. ( ͡~ ͜ʖ ͡°)

Full text and comments »

  • Vote: I like it
  • +239
  • Vote: I do not like it

171.
Codeforces Round 1029 (Div. 3)
By yse, 15 months ago, In English
Codeforces Round 1029 (Div. 3) أهلاً, Codeforces! ---------------------- [user:cry,2025-06-04], [user:Intellegent,2025-06-04], and I are really excited to invite you to participate in [contest:2117], which will take place on [contest_time:2117]. You will be given $2$ hours and $15$ minutes to solve $8$ problems. The round will be hosted by rules of educational rounds (extended ICPC). Thus, all solutions will be judged on preliminary tests during the round, and after the round, there will be a 12-hour phase of **open hacks**. After the open hack phase, all accepted solutions will be rejudged on successful hacks. Also, note that there is no score distribution but the usual penalty of **10 minutes** for each wrong submission, following the rules of educational rounds. Note that the penalty for each wrong submission in this round is **10 minutes**. Also, **note the rule [restricting AI use](https://codeforces.me/blog/entry/133941)**. If you are caught using AI in an unorthodox manner, you will be sent to [use...
Good luck, and most importantly, have fun!

Full text and comments »

  • Vote: I like it
  • +361
  • Vote: I do not like it

172.
JOI Spring Training 2025 Online Contest
By E869120, 18 months ago, In English
JOI Spring Training 2025 Online Contest Hello, everyone! Japanese Olympiad in Informatics (JOI) Spring Training 2025 ([Contest URL](https://contests.ioi-jp.org/joi-sp-2025/index-en.html)) will be held from March 21st to 24th. There are 4 days in the contest. * Day 1: [March 21, 02:00 GMT &mdash; March 21, 24:00 GMT](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympiad+in+Informatics+%28JOI%29+Spring+Camp+2025+Day1&iso=20250321T02&p1=1440&ah=22) * Day 2: [March 22, 02:00 GMT &mdash; March 22, 24:00 GMT](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympiad+in+Informatics+%28JOI%29+Spring+Camp+2025+Day2&iso=20250322T02&p1=1440&ah=22) * Day 3: [March 23, 02:00 GMT &mdash; March 23, 24:00 GMT](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympiad+in+Informatics+%28JOI%29+Spring+Camp+2025+Day2&iso=20250322T02&p1=1440&ah=22) * Day 4: [March 24, 02:00 GMT &mdash; March 24, 24:00 GMT](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Japanese+Olympia...
We welcome all participants. Good luck and have fun!

Full text and comments »

Tags joi, ioi
  • Vote: I like it
  • +211
  • Vote: I do not like it

173.
Algorithm Gym :: Graph Algorithms
By PrinceOfPersia, 12 years ago, In English
Algorithm Gym :: Graph Algorithms Welcome to the new episode of [user:PrinceOfPersia,2015-01-31] presents: Fun with algorithms ;) You can find all the definitions here in the book "Introduction to graph theory", Douglas.B West. [cut] Important graph algorithms : DFS --- The most useful graph algorithms are search algorithms. DFS (Depth First Search) is one of them. While running DFS, we assign colors to the vertices (initially white). Algorithm itself is really simple : ~~~~~ dfs (v): color[v] = gray for u in adj[v]: if color[u] == white then dfs(u) color[v] = black ~~~~~ Black color here is not used, but you can use it sometimes. Time complexity : $O(n + m)$. #### DFS tree DFS tree is a rooted tree that is built like this : ~~~~~ let T be a new tree dfs (v): color[v] = gray for u in adj[v]: if color[u] == white then dfs(u) and par[u] = v (in T) ...
Welcome to the new episode of [user:PrinceOfPersia,2015-01-31] presents: Fun with algorithms ;)

Full text and comments »

  • Vote: I like it
  • +355
  • Vote: I do not like it

174.
Codeforces Round 679 (Div.1, Div.2) and Technocup — Elimination Round 1
By Golovanov399, 6 years ago, translation, In English
Codeforces Round 679 (Div.1, Div.2) and Technocup — Elimination Round 1 Hi all! This weekend, at [contest_time:1413] we will hold Codeforces Round 679. It is based on problems of Technocup 2021 Elimination Round 1 that will be held at the same time. Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at <a href="https://technocup.mail.ru/">Technocup 2021 website</a> and take part in the Elimination Round. Div. 1 and Div.2 editions are open and rated for everyone. Register and enjoy the contests! The Elimination Round authors are [user:AndreySergunin,2020-10-24], [user:Endagorion,2020-10-24], [user:amethyst0,2020-10-24], and me, [user:Golovanov399,2020-10-24]. Thanks to [user:KAN,2020-10-24] and [user:300iq,2020-10-24] for their coordination. This round would also be not possible without the help of our testers: [user:__rkm__,2020-10-24], [user:300iq,2020-10-25], [user:arjunsanjeev7,2020-10-24], [user:brunomont,2020-10-24], [user:Chocobar,2020-10-24], [user:iankury,2020-10-2...
Have fun!

Full text and comments »

  • Vote: I like it
  • +237
  • Vote: I do not like it

175.
Codeforces Round 1045 (Div. 2)
By henotrix, 12 months ago, In English
Codeforces Round 1045 (Div. 2) Hello, Codeforces! I am glad to invite you to take part in [contest:2134], which will start on [contest_time:2134]. You will have $2$ hours to solve $6$ problems. The score distribution is listed below. There will be at least one interactive problem, so make sure to read the [guide for interactive problems](https://codeforces.me/blog/entry/45307) before the contest. The round will be rated for participants whose rating is below $2100$, but higher rated users are also welcome to participate out of competition. The problems were authored and prepared by me. I would like to thank: - [user:SSerxhs,2025-08-24] for coordination and providing great ideas to improve the problem set. - [user:Alexdat2000,2025-08-24] for translating the statements to Russian. - Our list of testers for providing valuable feedback: [user:StarSilk,2025-08-24], [user:BurnedChicken,2025-08-24], [user:Misuki,2025-08-24], [user:__baozii__,2025-08-24], [user:_istil,2025-08-24], [user:A_G,2025-08-24],...
Good luck & have fun!

Full text and comments »

  • Vote: I like it
  • +328
  • Vote: I do not like it

176.
Codeforces Round 1040 (Div. 1, Div. 2)
By wuhudsm, history, 13 months ago, In English
Codeforces Round 1040 (Div. 1, Div. 2) Hello, Codeforces! We're glad to invite you to take part in [contest:2129] and [contest:2130], which will start on [contest_time:2129]. You will be given **6 problems** and **3 hours** to solve them in both divisions. Some problems will be divided into subtasks. The problems were authored and prepared by me. Some problems may be **interactive**. So please refer to the guide on [interactive problems](https://codeforces.me/blog/entry/45307) if you are unfamiliar with them. We would like to thank - [user:TheScrasse,2024-04-28] and [user:errorgorn,2025-07-30] for the coordination; - [user:Alexdat2000,2024-04-28] for Russian translation; - [user:Burnedchicken,2025-07-30], who impressively solved $15$ problems, for **VIP++** testing; - [user:StarSilk,2025-07-30], [user:liympanda,2025-07-30], [user:Irmuun.Ch,2025-07-30], [user:irkstepanov,2025-07-30], [user:nifeshe,2025-07-30], [user:Error_Yuan,2025-07-30], [user:Akulyat,2025-07-30], [user:sevlll777,2025-07-30], [user:Fairy...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +286
  • Vote: I do not like it

177.
WF23 Luxor
By galen_colin, 2 years ago, In English
WF23 Luxor _(Long blog ahead. Reader discretion advised.)_ I feel we have a rather interesting WF story (note: we did the 47th finals, as the University of Maryland, <b><i>as 2 people</i></b>... explained below), so I figured I'd tell it. Exposition ---------- It actually starts way before WF, too. Our teams were decided on (some form of) merit based on an internal qualifier. My team for the regional and NAC (North America superregional) ended up as {me, [user:Navick,2024-04-24], [user:mr.banana,2024-04-24]}. We did [fairly](https://nasouth22d1.kattis.com/contests/nasouth22d1/standings) [well](https://nac.icpc.global/wp-content/uploads/2023/06/NAC23-scoreboard.pdf) in those. However, for WF, my two teammates only had single-entry visas for the US, meaning that if they left, they couldn't come back into our country. So they couldn't really go with me... Luckily, in such situations, ICPC lets you just replace your teammates. So we held another internal qualifier, and ended up with two ...
for over 12 hours, which could not have been a fun process to go through. However, we supposed that, that was it for him, and that couldn't have been a fun process at all, especially since it all ended

Full text and comments »

  • Vote: I like it
  • +457
  • Vote: I do not like it

178.
Codeforces Round #825 (Div. 2)
By satyam343, 4 years ago, In English
Codeforces Round #825 (Div. 2) Hello, Codeforces! [user:lackadaisical_lad,2022-10-07], [user:naman1601,2022-10-07] and I are glad to invite everyone to participate in [contest:1736], which will be held on [contest_time:1736]. This Round will be rated for participants with rating lower than **2100**. You will be given **5 problems with one subtask** and **2 hours** to solve them We would like to thank: - [user:Arpa,2022-10-07] for coordinating the round. - [user:KAN,2022-10-07] for help in preparation of the round. - [user:Everule,2022-10-07] for proposing a task that did not make it to the final problemset. - [user:BucketPotato,2022-10-07], [user:PurpleCrayon,2022-10-07], [user:the_hyp0cr1t3,2022-10-07], [user:welleyth,2022-10-07], [user:MagentaCobra,2022-10-07], [user:recurring_raj,2022-10-07], [user:GoatTamer,2022-10-07], [user:udhavvarma03,2022-10-07], [user:74TrAkToR,2022-10-07], [user:AwakeAnay,2022-10-07], [user:cadmiumky,2022-10-07], [user:TheScrasse,2022-10-07], [user:kal013,2022-10-07]...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +318
  • Vote: I do not like it

179.
VK Cup 2016 — Round 3
By Errichto, 10 years ago, In English
VK Cup 2016 — Round 3 Hi everybody. The VK Cup Round 3 is coming ([exact time](http://www.timeanddate.com/worldclock/fixedtime.html?day=7&month=5&year=2016&hour=18&min=5&sec=0&p1=166)). The duration will be longer than usual, likely 3 hours. As usually in VK Cup, there will be three contests &mdash; div1, div2, official one. All of them are rated. Div1 and div2 versions are for individual participants, not for teams. Setters are [user:Stonefeang,2016-05-05], [user:Errichto,2016-05-05] and [user:qwerty787788,2016-05-05]. I think that (some) problems are extremely interesting and I really wish I could participate. Thanks to [user:GlebsHP,2016-05-05] and [user:MikeMirzayanov,2016-05-05], we wouldn't have a round without them. Also, thanks to [user:AlexFetisov,2016-05-06] and [user:winger,2016-05-06] for testing. We will later inform about the final duration. Maybe we will inform about the number of problems and scoring. I wish you great fun and no frustrating bugs. And Limak wishes you...
I wish you great fun and no frustrating bugs. And Limak wishes you good luck!

Full text and comments »

Announcement of VK Cup 2016 - Round 3
  • Vote: I like it
  • +327
  • Vote: I do not like it

180.
Codeforces Round 350
By MikeMirzayanov, history, 10 years ago, translation, In English
Codeforces Round 350 <img src="http://codeforces.me/predownloaded/57/00/5700ddd1b3c541fe2021c83fefdd6b80d5d5370c.png" style="float:right; margin:0 1em 1em 1em;"/> On [May, 5, 16:05 (UTC)]( http://timeanddate.com/worldclock/fixedtime.html?day=5&month=5&year=2016&hour=19&min=5&sec=0&p1=166) Codeforces Round 350 is going to start! Yes, pay attention to _the non-standard start time_. I took advantage of my official position and the round is expected to be a bit experimental with an expanded set of problems. Perhaps for experienced participants (sorry, Div 1) it could seem easy. This time, emphasis was placed on the main target audience of the round: so in the round will be a lot of very simple problems, but even the top of the second division will find something interesting. In addition, one of the problems will be offered in two versions &mdash; in a simplified version with small constraints and in a harder version with greater constraints. Thus, if you immediately realize solution for large constraint...
problems and the round will be fun and useful!

Full text and comments »

Tags 350
  • Vote: I like it
  • +466
  • Vote: I do not like it

181.
Codeforces Round #785 (Div. 2)
By JaySharma1048576, 4 years ago, In English
Codeforces Round #785 (Div. 2) Hello Codeforces, I invite you to participate in [contest:1673] which will be held on [contest_time:1673]. **The round will be rated for participants of Division 2 with rating strictly less than 2100**. But as always, the participants of Division 1 are welcome to take part out of competition. You will be given **6 problems** and **2 hours** to solve them. Moreover, there will be atleast $1$ and atmost $1048576$ interactive problems. So, you are advised to refer to the [guide on interactive problems](https://codeforces.me/blog/entry/45307) in case you are not familiar with them. I would like to thank the following people for their contribution to the round: - [user:Artyom123,2022-04-28] for his amazing coordination, helping me throughout the preparation of the round and translating the statements. - [user:Um_nik,2022-04-28], [user:Monogon,2022-04-28], [user:kclee2172,2022-04-28], [user:TheScrasse,2022-04-28], [user:yash_daga,2022-04-28], [user:Sad_reacts_only,2022-04-28], ...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +369
  • Vote: I do not like it

182.
Educational Codeforces Round #1
By Edvard, history, 11 years ago, translation, In English
Educational Codeforces Round #1 Привет, Codeforces! [13 ноября 2015 года в 18:00 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?msg=Educational+Codeforces+Round+%231&iso=20151113T1500) состоится первый учебный раунд Educational Codeforces Round #1 для участников из первого и второго дивизионов. Учебные раунды Codefores &mdash; это новый формат соревнований основной целью, которого является помощь в развитии у участников базовых (и не только) навыков и знаний, которые необходимы при решении олимпиадных задач по программированию. В учебных раундах вы встретите не только старые добрые идеи и алгоритмы, которые многие знают, но также и некоторые расширенные темы, которые неизвестны многим участникам, в том числе и из первого дивизиона. Сложность задач будет сравнима с обычными раундами для участников из второго дивизиона, хотя многое может пригодиться и участникам из первого дивизиона. На мой взгляд первый раунд получился несколько проще того на что мы ориентировались. Учебные раунды будут нерейтингов...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +231
  • Vote: I do not like it

183.
Codeforces Round #349 (Div. 1 & Div. 2)
By adamant, 10 years ago, translation, In English
Codeforces Round #349 (Div. 1 & Div. 2) Hi everyone! Yeah, you guessed it right, after a long four month break after the [latest div. 1 round](http://codeforces.me/blog/entry/22726) which was not dedicated to any official competition, you will once again have the unique opportunity to participate in **usual** codeforces round. No t-shirts for _top-x_ competitors! No multi-level selection system for the opportunity to compete in final! No esoteric languages or marathon-like problems! We even will not tell you the scoring untill the very end of the round! That's it, like the good old days. So this round was prepared for you by Ivan Smirnov ([user:ifsmirnov,2016-04-28]) and me ([user:adamant,2016-04-28]). We want to thank Max Akhmedov ([user:Zlobober,2016-04-28]), Alex Frolov ([user:fcspartakm,2016-04-28]), Edvard Davtyan ([user:Edvard,2016-04-28]) and Mike Mirzayanov ([user:MikeMirzayanov,2016-04-28]) for the help in round preparing, and useful advice. Special thank to [user:Edvard,2016-04-28] for taking the role of c...
Good luck to everyone! We really hope that you will have a lot of fun participating in this round :)

Full text and comments »

  • Vote: I like it
  • +694
  • Vote: I do not like it

184.
OMORI CONTEST Announcement
By Hexagons, 23 months ago, In English
OMORI CONTEST Announcement Assalamualaikum (peace be upon you), Codeforces people &#128075;. I'm glad to invite you to the mashup [OMORI CONTEST](https://codeforces.me/contestInvitation/fc8da6d6845e77adc452e754d3d84c1086148c59) which will be held inshallah on [Thursday, October 17, 2024 at 19:30 (GMT+3)](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20241017T1930&p1=426). You will be given **3.5 hours (210 minutes)** to solve **7 cool problems** in an **ICPC-styled** contest, themed about the videogame [OMORI](https://www.google.com/search?q=omori) (Which is a great game that you might want to give a try). There will be exactly one interactive problem, so I suggest you should read the [guide for interactive problems](https://codeforces.me/blog/entry/45307). All problems have been written and prepared by me, [user:Hexagons,2024-10-04]. I would like to give a lot of thanks to: - [user:MikeMirzayanov,2024-10-04] for the great codeforces and polygon systems &#128077;, without them I wou...
discouraged to use it. This is just a fun mashup that has not real life (or even virtual life) consequences, I Hope you enjoy the contest and have fun solving the problems 😊.

Full text and comments »

Announcement of OMORI CONTEST
  • Vote: I like it
  • +370
  • Vote: I do not like it

185.
COMPFEST 15 Preliminary Online Mirror (Unrated, ICPC Rules, Teams Preferred)
By Pyqe, history, 3 years ago, In English
COMPFEST 15 Preliminary Online Mirror (Unrated, ICPC Rules, Teams Preferred) <img alt="logo" src="/predownloaded/54/ec/54ec8a2a974eb225636db378f5470e039144d49b.png" style="float: right;height: 100.0px;margin: 10.0px;max-width: 100.0%;max-height: 100.0%;"> Hello, **Codeforces**! &#x1f60d;&#x1f60d; We are happy to invite you to participate in [COMPFEST 15 Preliminary Online Mirror (Unrated, ICPC Rules, Teams Preferred)](https://codeforces.me/contests/1866) on <a class="contest-time" contestid=1866></a>. COMPFEST is a national **ICPC-style contest** for university students in Indonesia. The problems are written and prepared by [user:ArvinCiu,2023-08-30], [user:asteriskzie,2023-08-30], [user:CyberSleeper,2023-08-30], [user:Edbert.H,2023-08-30], [user:FreeJinG,2023-08-30], [user:gansixeneh,2023-08-30], [user:KokiCoder,2023-08-30], [user:nandonathaniel,2023-08-30], and [user:Pyqe,2023-08-30]. We would also like to thank: - [user:KAN,2023-08-30] for helping to host the mirror round; - [user:AMnu,2023-08-30], ([user:KerakTelor,2023-08-30], [user:Owmic...
We hope you will enjoy and have fun in the contest. Good luck! 🔥🔥🔥🔥

Full text and comments »

  • Vote: I like it
  • +308
  • Vote: I do not like it

186.
ZeptoLab Code Rush 2015
By viktork, 11 years ago, translation, In English
ZeptoLab Code Rush 2015 Hello, Codeforces! <b><i>The problems were suggested by users [user:roosephu,2015-04-04] and [user:sunayuki,2015-04-04]. The great help in preparing was provided by [user:Aksenov239,2015-04-04], [user:GlebsHP,2015-04-04] and Codeforces team. ZeptoLab Team did its best while working on statements.</i></b> <b><i>The round will use smoother dynamic problem scores with 250 points steps.</i></b> In 2014 we hosted our [first programming contest](/zeptolab2014) together with Codeforces, and we liked it! Let me shortly remind you how it was. The contest consisted of 6 problems, 2.5 hours were given to solve (you can have a look at the problems of the previous year and try to solve them [here](/contest/436)). Of course, even on a purely coding event we stayed true to ourselves, so all problems were designed based on our games, and, of course, we illustrated them with care: <center> <img src="http://assets.codeforces.com/images/zepto2015/pics2014.jpg"/> </center> Zepto C...
fun gizmos of our corporate green color).

Full text and comments »

Announcement of ZeptoLab Code Rush 2015
  • Vote: I like it
  • +886
  • Vote: I do not like it

187.
Codeforces Round #822 (Div.2) Editorial
By arvindf232, 4 years ago, In English
Codeforces Round #822 (Div.2) Editorial Thank you for your participation! [1734A &mdash; Select Three Sticks](https://codeforces.me/contest/1734/problem/A) ------------------ We first sort the array $a$ in non-decreasing order. Denote the indices of the elements that we choose from $a$ to be $x$, $y$, and $z$, where $1 \le x < y < z \le n$, and the final value (after performing the operations) of the concerned elements to be $v$. The minimum required number of operations is then $|a_x-v|+|a_y-v|+|a_z-v|$. It is well-known that such expression attains its minimum value when $v$ is the median of $a_x$, $a_y$, and $a_z$. Since the array $a$ has already been sorted, it is best to assign $v$ to be $a_y$. Our expression then becomes $|a_x-a_y|+|a_y-a_y|+|a_z-a_y|=(a_y-a_x)+0+(a_z-a_y)=a_z-a_x$. We would like to minimize the value of $a_z$, which implies $z$ should be as small as possible since $a$ is sorted. It is clear that taking $z=y+1$ would minimize the value of the expression. Similarly, we can show that we ...
~~~~~ val Boolean.chi:Int get() = if(this) 1 else 0 //characteristic function fun Int.has(i:Int

Full text and comments »

  • Vote: I like it
  • +169
  • Vote: I do not like it

188.
Codeforces Round #554 (Div. 2)
By AkiLotus, history, 7 years ago, In English
Codeforces Round #554 (Div. 2) Once again, **TREMBLE BEFORE THE MIGHTY OMEGALULRIPGRAPE.** ![ ](https://i.imgur.com/kpS7NEq.png) ![ ](https://i.imgur.com/A2dF7M2.jpg) *(He last walked the Earth in round [538](https://codeforces.me/blog/entry/65033) btw.)* Hello Codeforces! We are here to invite you to Codeforces Round #554 (Div. 2), which will take place at [contest_time:1152]. The round will be rated for all Division 2 participants **(with rating less than 2100)**, yet any Division 1 participants are welcome to join us out of competition. The round will be cat themed. Raise your paws and prepare your catnips! *(Or even cat memes, while you're at it).* You will be given **6+1** problems ( **6** problems, one of them has **2** subtasks ) to solve in **2 hours.** The round's problems were prepared by Xuan-Quang ~xuanquang1999,2019-04-23 D. Nguyen, Duy-Bach ~Akikaze,2019-04-23 Le, Stefan ~stefdasca,2019-04-23 Dascalescu, Quang-Minh ~MofK,2019-04-23 D. Nguyen and our dear Codeforces coordinator ...
**UPD1a:** Another comrade, Quang-Minh ~MofK,2019-04-23 D. Nguyen joined the fun ! Kudos for the

Full text and comments »

  • Vote: I like it
  • +436
  • Vote: I do not like it

189.
Codeforces Round 896 (Div. 1, Div. 2)
By sszcdjr, 3 years ago, In English
Codeforces Round 896 (Div. 1, Div. 2) Hello, Codeforces! & Happy Chinese Teachers' Day! We (OICon Team) are so excited to invite you to take part in OICon Round 1 ([contest:1868] and [contest:1869]) which will start on [contest_time:1868]. You will be given 6 problems and 2.5 hours to solve them in both divisions. * **Please notice the unusual starting time!** * One of the problems has two versions but their statement are not exactly the same, which means that you **can't** pass the easy version using the code of the hard version. However, you can only make hacks when you pass both versions. * There will be $0$ interactive problem in each division so you needn't read the [guide for interactive problems](https://codeforces.me/blog/entry/45307). * Score distribution: * Div. 1: $500-(500+750)-1000-1750-2500-3000$ * Div. 2: $500-750-1250-(1250+1500)-2500-3250$ The problems were authored and prepared by [user:Error_Yuan,2023-09-03], [user:duck_pear,2023-09-03], [user:programpiggy,2023-09-03] and me. We...
Good Luck & Have Fun!

Full text and comments »

  • Vote: I like it
  • +350
  • Vote: I do not like it

190.
Rumination on AI and competitive programming
By ko_osaga, history, 2 years ago, In English
Rumination on AI and competitive programming An OpenAI model can now achieve a rating of 1800 in Codeforces. That made me wonder about the future of competitive programming and why we do this. I came up with some opinions, which I'll be glad to share with you. ## AI killed the competitive programming? I don't think that's happening, because competitive programming is useless! Some people might think CP is less interesting because AI can solve CP problems &mdash; but come on, problemsetter can solve those problems, unless they are really bad. Many people still play Chess just fine, and I recently enjoyed participating in Sudoku competitions, although I was completely aware that computers would wreck me in a second. It didn't matter, and I didn't see how it could. CP problems are not "open problems" &mdash; if they are, the problemsetters are to blame. So, you are not contributing anything to the world by solving CP problems; it all comes down to personal interest. As long as CP is fun for people, they will do it. ## Flag...
interest. As long as CP is fun for people, they will do it., will limit lots of fun problems. The one problem that AI did [relatively terribly on IOI is Mosaic

Full text and comments »

  • Vote: I like it
  • +255
  • Vote: I do not like it

191.
Codeforces Round #747 (Div. 2)
By Theo830, 5 years ago, In English
Codeforces Round #747 (Div. 2) Γεια σου (Hello), Codeforces! [user:Dremix10,2021-10-01] and I are glad to invite you to the first **Cypriot round** [Codeforces Round #747 (Div. 2)](https://codeforces.me/contest/1594) which will take place on [contest_time:1594]. **Note the unusual start time of the round**. As usual, **this round will be rated for participants with rating lower than 2100.** Problems were created and prepared by [user:Dremix10,2021-10-01] and me. We tried to make them interesting, with short and clear statements. We hope that you will enjoy them! I would like to thank: - [user:adedalic,2021-10-01] for amazing coordination of this round. - [user:Dremix10,2021-10-01] for giving the first feedback about every problem I created. - [user:Markadiusz,2021-10-01], [user:cfalas,2021-10-01], [user:m371,2021-10-01], [user:ijxjdjd,2021-10-06], [user:YouKn0wWho,2021-10-06], [user:PurpleCrayon,2021-10-06], [user:flamestorm,2021-10-06], [user:Shinchan01,2021-10-06], [user:rgnerdplayer,2021-...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +586
  • Vote: I do not like it

192.
The Toxic Mindset in Competitive Programming and How to Fight It
By SlavicG, history, 4 years ago, In English
The Toxic Mindset in Competitive Programming and How to Fight It #### Introduction Rating is a great measure of skill and a nice way to observe progress by comparing yourself to your past self and seeing where you stand in the community. As great measure as it is, there are a lot of problems that come with it. They have nothing to do with how the rating system works but rather with how human beings function. In this blog post, I will talk about some of the most pressing personal problems that come up with rating and try to provide some advice on how to solve them, speaking from personal experience and from the experience of a lot of other people I know. #### Associating self-worth to rating This is, in my opinion, the most significant problem people face, and it also pretty much contains all the following problems as a subset. It's extremely easy to fall into this rabbit hole since, as a competitive programmer, it only feels natural to associate our rating with intelligence and, respectively, our intelligence with self-worth. Why is this su...
, learn about new topics and just have fun.

Full text and comments »

  • Vote: I like it
  • +432
  • Vote: I do not like it

193.
Ethflow Round 1 (Codeforces Round 1001, Div. 1 + Div. 2)
By StarSilk, history, 19 months ago, In English
Ethflow Round 1 (Codeforces Round 1001, Div. 1 + Div. 2) Hi Codeforces! As the Chinese New Year approaches, we are glad to invite you to our Codeforces Round [contest:2062] which will be held on [contest_time:2062]. You will be presented with $8$ problems, one of which is divided into two subtasks, and $2.5$ hours to solve them. This round will be rated for all participants. This round is the first Div. 1 + Div. 2 round on Codeforces with a four-digit round number, and it is also my first round. We hope you will enjoy this round. Great thanks to: - [user:SSerxhs,2025-01-23] for helping me prepare most problems, - [user:Yakumo_Ran,2025-01-23] for providing some problems, - [user:TheScrasse,2025-01-23] for good coordination of this round, - [user:alexdat2000,2025-01-23] for translating all statements to Russian, - [user:jqdai0815,2025-01-23], [user:ugly2333,2025-01-23], [user:dXqwq,2025-01-23], [user:Sugar_fan,2025-01-23], [user:propane,2025-01-23], [user:LuCpp,2025-01-23], [user:triple__a,2025-01-23], [user:PinkieRabbit,20...
Good luck & Have fun!

Full text and comments »

  • Vote: I like it
  • +220
  • Vote: I do not like it

194.
Editorial of Global Round 15
By cip999, 5 years ago, In English
Editorial of Global Round 15 We hope you liked the problems! Before we go ahead with the editorial, let us make some general comments about this round. Problems A, B, C, D, E, F are "div 2" problems, while problems G, H, I are meant to be solved by Grandmasters. Overall, our goal was to provide a problemset that could be enjoyable for a wide range of participants and such that the winner could solve all the problems. There were three big "jumps" in the difficlty gaps between consecutive problems. Problems A and B are meant to be easy, many contestants have the skills and the techniques to attack them (and, maybe, to solve them). Problems C, D, E, F are gradually harder but the difficulty gap between C and F is not as large as usual (and this is reflected in the score distribution). The same holds for problem G, H, I; the difficulty gap between G and I is relatively small (but there is a big score difference because coding I is much harder). Sadly, we discovered 14 minutes into the round that problem I...
not touch elements which are already in the correct position! Fun fact: this problem appears again, I had a whole lot of fun organizing Global Round 15, and I discovered that I like inventing

Full text and comments »

  • Vote: I like it
  • +533
  • Vote: I do not like it

195.
A Brief Inquiry into Online Connectivity
By ko_osaga, history, 3 years ago, In English
A Brief Inquiry into Online Connectivity This question striked my head: *"How can I solve dynamic $k$-connectivity efficiently?"* And then I tried to answer it, but I realized that my question was open to a lot of different interpretations. Two vertices are $k$-connected if there are $k$ edge-disjoint paths connecting two vertices. For $k = 1$, it is the usual definition of *connectivity*. ## Solve? If I say, "I solved the graph connectivity problem", what can it possibly mean? **First Interpretation ($s$-$t$ connectivity)**. I can respond to the following query efficiently: Given two vertices $s, t$, determine if there is a path between them. In the case of $k = 1$, graph search suffices. What about higher $k$? You can find $k$ edge-disjoint path by reducing it into a flow problem. Each edge-disjoint path corresponds to a flow from $s$-$t$, so make all edges to capacity one, and find a flow of total capacity $k$ from $s$ to $t$. This algorithm takes $O(\min(k, m^{1/2}) (n + m))$ time. **Second Interpre...
fun.

Full text and comments »

  • Vote: I like it
  • +143
  • Vote: I do not like it

196.
Codeforces Round 871 (Div. 4)
By SlavicG, history, 3 years ago, In English
Codeforces Round 871 (Div. 4) Hey, hi Codeforces! It's [user:mesanu,2023-03-18], [user:flamestorm,2023-03-18] and me and we are very excited to invite you to [contest:1829]! It starts on [contest_time:1829]. We worked swiftly to tailor the problems for this contest, so we hope you will enjoy them! We tried to make the statements short, epic and concise. The format of the event will be identical to Div. 3 rounds: - 5-8 tasks; - ICPC rules with a penalty of 10 minutes for an incorrect submission; - 12-hour phase of open hacks after the end of the round (hacks do not give additional points) - after the end of the open hacking phase, all solutions will be tested on the updated set of tests, and the ratings recalculated - by default, only "trusted" participants are shown in the results table (but the rating will be recalculated for all with initial ratings less than 1400 or you are an unrated participant/newcomer). We urge participants whose rating is 1400+ not to register new accounts for the purpose...
**Good Luck and have fun!!**

Full text and comments »

  • Vote: I like it
  • +238
  • Vote: I do not like it

197.
EPIC Institute of Technology Round August 2024 (Div. 1 + Div. 2)
By xcyle, 2 years ago, In English
EPIC Institute of Technology Round August 2024 (Div. 1 + Div. 2) <a href="https://epic-institute.io/"><img alt="EPIC" src="https://assets.codeforces.com/images/deltix/2_logo.gif" style="float:right; height: 154px; padding-left: 35px; padding-right: 73px; padding-top: 41px; padding-bottom: 33px;"/></a> Hi, Codeforces! We are pleased to invite you to [contest:2002], which will be held on [contest_time:2002]. The problems are prepared by [user:Flamire,2024-08-06], [user:le0n,2024-08-06] and [user:xcyle,2024-08-06]. You will be given **8 problems** and **3 hours** to solve them. Two problems are divided into two subtasks. The round will be rated for **everyone**. We would like to thank everyone who has helped prepare for this round: - [user:TheScrasse,2024-08-06] for his brilliant coordination. - [user:AdunAdunov,2024-08-08] and [user:Alexdat2000,2024-08-08] for Russian translation. - [user:orzdevinwang,2024-08-06], [user:arvindf232,2024-08-08], [user:MagicalFlower,2024-08-06], [user:rui_er,2024-08-06], [user:LipArcanjo,2024-08-06], [u...
Good luck, have fun!

Full text and comments »

  • Vote: I like it
  • +293
  • Vote: I do not like it

198.
Codeforces Global Round 10 — Editorial
By Tlatoani, 6 years ago, In English
Codeforces Global Round 10 — Editorial We hope you liked the problems! We apologize for the weak pretests for A and B -- that was a major oversight on our part. Hopefully you were still able to enjoy the contest regardless :) We have to apologize to [user:antontrygubO_o,2020-08-16] a bit here -- the rejection count mentioned in the [editorial](https://codeforces.me/blog/entry/79974) for [contest:1372] actually also included this round, as the problems from that round and problems A through G in this round were created together. We did have one more problem rejected after that round happened, bringing up the total to 73. For reference, here are the overall rejection counts for each problem: <spoiler summary="Rejection Counts"> - A: 12 - B: 16 - C: **6** - D: 19 - E: 18 - F: 2 Total: **73** </spoiler> Without further ado, here are the tutorials for each of the problems: [tutorial:1392A] <spoiler summary="Solution (Kotlin) by golions"> ~~~~~ import java.io.* import java.util.* import kotlin.math...
fun main(){ val f = BufferedReader(InputStreamReader(System.`in`))

Full text and comments »

  • Vote: I like it
  • +214
  • Vote: I do not like it

199.
Codeforces Round #228
By cgy4ever, 13 years ago, In English
Codeforces Round #228 Hello everyone! [Codeforces Round #228](http://codeforces.me/contests/388,389) (Div. 1 and Div.2) will start at [Monday, 3 February 2014, 19:30:00 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?day=3&month=2&year=2014&hour=19&min=30&sec=0&p1=166). This is my 2nd round on Codeforces. (Click [here](http://codeforces.me/blog/entry/8163) to see my last round) , As usual, there will be 7 problems: 2 for Div2, 2 for Div1 and 3 for both. And same with the last round, the main character of all problem will be Fox Ciel. I would like to thank [user:Gerald,2014-02-01] for testing, and [user:MikeMirzayanov,2014-02-01] for the Codeforces project including [polygon](http://polygon.codeforces.com) system. Good luck and have fun! The score distribution will be published later. And the editorial will be published right after the system test. By the way, yesterday is the Chinese new year. So I'd like to say Happy New Year to everyone who celebrate it! And I'm very glad ...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +313
  • Vote: I do not like it

200.
Codeforces Round 1035 (Div. 2)
By CutieSmileHaruka, history, 14 months ago, In English
Codeforces Round 1035 (Div. 2) 你好，Codeforces！ We (FeOI and WAOI Team) are glad to invite you to take part in [contest:2119], which will start on [contest_time:2119]. You will be given **6 problems** and **2 hours** to solve them. The round will be rated for participants of Division 2 with a rating lower than **2100**. Division 1 participants can participate unofficially. All problems are authored by [user:lizhous,2025-06-28], [user:Lyz09,2025-06-28], [user:ma2021tyoi0037,2025-06-28] and me. I would like to thank the following people for making this round possible: - [user:abc864197532,2025-06-28] for the excellent coordination. - [user:Alexdat2000,2025-06-28] for Russian translation. - [user:lizhous,2025-06-28], [user:Lyz09,2025-06-28], [user:Rebex,2025-06-28], [user:hzy_mod,2025-06-28] and me for providing some rejected problems. - [user:Z-301,2025-06-28] for Legendary Grandmaster Testing. He was promoted from IGM to LGM four days after testing, congratulations! - [user:Fysty,2025-06-28], [user:_...
We hope you will enjoy and have fun in the contest.

Full text and comments »

  • Vote: I like it
  • +297
  • Vote: I do not like it

201.
Codeforces Round #334
By desert97, history, 11 years ago, In English
Codeforces Round #334 Howdy Codeforces! Come join us for a trip to Bovinia with everyone’s favorite munchkin Kevin Sun ([user:ksun48,2015-11-30]) and his sidekick Nicky Sun ([user:nsun48,2015-11-30])! Codeforces Round #334 (for both divisions) will be taking place on [December 1st, at 6:35pm MSK](http://www.timeanddate.com/worldclock/fixedtime.html?day=1&month=12&year=2015&hour=18&min=35&sec=0&p1=166). The problems were written by Alex Wei ([user:yummy,2015-11-30]), Michael Kural ([user:pi37,2015-11-30]), and myself, Yang Liu. As proud Americans, we’ve themed all of our statements around the most glorious cow (and its many uses in life). ![ ](http://i.imgur.com/GaaxwrM.png) ![ ](http://i.imgur.com/YbpRD2Q.png) We are immensely grateful to [user:GlebsHP,2015-11-30] for his guidance and suggestions, without whom we would not have a balanced problem set. In addition, we would like to thank [user:MikeMirzayanov,2015-11-30] for creating Codeforces and Polygon, as well as [user:Delinur,2015-11-30] for tr...
for Div 1. Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +466
  • Vote: I do not like it

202.
What to do at the IOI after you (inevitably) solve everything
By dolphingarlic, history, 6 years ago, In English
What to do at the IOI after you (inevitably) solve everything With IOI just around the corner, [some](https://codeforces.me/profile/tmwilliamlin168) [of](https://codeforces.me/profile/300iq) [you](https://codeforces.me/profile/saba2000) may be wondering: **"what should I do after I AK after 3 hours?"** In this post, I'll share some activities that you can do to pass the time! (Note that some of these may not be applicable for an online IOI) ## Level 1 &mdash; Built-in software on your computer The most obvious thing you can do is use the built-in stuff. I'm talking about playing Minesweeper, reading the C++ documentation, or anything similar. While Minesweeper is quite fun and the C++ documentation is... interesting, Minesweeper quickly becomes boring and you'll look like a huge nerd if you read the documentation (and you don't want that, do you?) That's why I'll only recommend this if you're a noob and only AK in 4 hours. ## Level 2 &mdash; Creating software So you've beaten Minesweeper 10 times already and read throug...
(or C++ if you're one of those people) is a fun (albeit not very rewarding) challenge. But you know, Ok, I get it — you're no fun and only want to do something related to the IOI. That's, While Minesweeper is quite fun and the C++ documentation is... interesting, Minesweeper quickly

Full text and comments »

  • Vote: I like it
  • +384
  • Vote: I do not like it

203.
Codeforces Round #487 (Div. 2)
By cyand1317, history, 8 years ago, In English
Codeforces Round #487 (Div. 2) Here and there, summer's in the air! (I beg your forgiveness, residents of the Southern Hemisphere... > <) I'm delighted to invite you to [contest:989], which starts at [contest_time:989]. Please note that the timing is, as usual, unusual. This is my third time creating a contest from scratch. Along the way can be seen the efforts of: [user:KAN,2018-06-10] the super-ultra-hyper-mega-meta coordinator, who has reviewed, refined and translated the problems; [user:300iq,2018-06-10], [user:Livace,2018-06-10], [user:mike_live,2018-06-10], [user:Noam527,2018-06-10], [user:RobeZH,2018-06-10], and [user:Tommyr7,2018-06-11] the super-ultra-great-delicious-wonderful testers, that have populated our collection of solutions; and [user:MikeMirzayanov,2018-06-10] along with the super-ultra-extreme-awesomazing Codeforces/Polygon team, who have made all these happen in the way it is! Kudos to all of you! The round will be **rated** for contestants from the second division, and the first divisi...
We wish everyone a fun experience and a fair rating. We'll be pleased to have you on the contest!

Full text and comments »

  • Vote: I like it
  • +444
  • Vote: I do not like it

204.
Introduction of Neowise Labs
By Edvard, 17 months ago, In English
Introduction of Neowise Labs Hello, Codeforces! I’m excited to introduce to you Neowise Labs. We’re going to host an upcoming [contest:2096] and have prepared presents for you. Neowise Labs was founded by Max ([user:dark_ai,2025-04-11]), Igor ([user:Igor_Kudryashov,2025-04-11]) and me, and here is our story. <center> <img style="width:400px;" src="/predownloaded/16/41/16415eb2b19a656db6f7e133296434dea3391a21.jpg"/> </center> [user:Igor_Kudryashov,2025-04-11] and I have been in the same ACM ICPC team for many years while studying at the Saratov State University. [user:dark_ai,2025-04-11] was in the Saint Petersburg State University team so we were competitors back then :) Those years in the university we were doing the same as all other competitive programmers: solve problems, make contests, practice, practice and practice again (and sometimes study). I’ve even enjoyed being a Codeforces platform developer in my final year of study. [cut] <center style="margin-top:30px;"> <img style="width:450...
Enjoy the contest, good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +204
  • Vote: I do not like it

205.
Google Kick Start 2021
By kostka, 5 years ago, In English
Google Kick Start 2021 Looking for a way to stay connected, try something new, and have a little fun? The [**Kick Start 2021**](https://codingcompetitions.withgoogle.com/kickstart?utm_medium=email&utm_source=toolkit%20template&utm_campaign=reg_promo&src=Online/TOPs/KS) season has begun! **Kick Start** offers **programmers of all skill levels** the opportunity to **boost your skills** through a series of intriguing algorithmic and mathematical problems designed by Google engineers. **Each round starts fresh**, so give any one of our 2021 online rounds a try — or join them all! **Join** * Create a [Coding Competitions profile](https://codingcompetitions.withgoogle.com/profile) and then [register](https://codingcompetitions.withgoogle.com/kickstart/register?utm_medium=email&utm_source=toolkit%20template&utm_campaign=reg_promo&src=Online/TOPs/KS) for Kick Start. * Check out [the full schedule](https://codingcompetitions.withgoogle.com/kickstart/schedule?utm_medium=email&utm_source=university_progr...
Looking for a way to stay connected, try something new, and have a little fun? The [**Kick Start, We hope you’ll join us for some fun practice. What are you waiting for?

Full text and comments »

  • Vote: I like it
  • +239
  • Vote: I do not like it

206.
Codeforces Round 908 (Div. 1, Div. 2)
By sevlll777, history, 3 years ago, In English
Codeforces Round 908 (Div. 1, Div. 2) Big greetings, Codeforces! I am happy to invite you to [contest:1893], [contest:1894], which will be held on [contest_time:1893]. This round will be **rated for everyone**. In both divisions, you will be given **5 problems** and **120 minutes** to solve them. All problems were cooked by me ([user:sevlll777,2023-10-31]). The traditional thanks-list to everyone who took part in the creation of the round. Thanks, - [user:74TrAkToR,2023-10-31] for incredible coordination! - [user:gzchenben,2023-10-31], [user:Gary2005,2023-10-31], [user:SomethingNew,2023-10-31], [user:Heltion,2023-10-31], [user:FairyWinx,2023-10-31], [user:EternalAlexander,2023-10-31], [user:RUSH_D_CAT,2023-10-31], [user:rsj,2023-10-31], [user:Kieray,2023-10-31], [user:CtrlAlt,2023-10-31], [user:Vladithur,2023-10-31], [user:nnv-nick,2023-10-31], [user:AndZhi,2023-10-31], [user:p_b_p_b,2023-10-31], [user:Adam_GS,2023-10-31], [user:tem_shett,2023-10-31], [user:127.0.0.1,2023-10-31], [user:a.nasretdinov,2023-10...
Have fun!

Full text and comments »

  • Vote: I like it
  • +175
  • Vote: I do not like it

207.
India ICPC — Gwalior-Pune 2020 Regionals
By T1duS, history, 5 years ago, In English
India ICPC — Gwalior-Pune 2020 Regionals Hi Codeforces, **ICPC Gwalior-Pune 2020 Regional Round will be held on [Codedrills](https://codedrills.io/) tomorrow.** **Contest Details** - Contest Link — [ICPC Gwalior-Pune 2020 Regional Round](https://codedrills.io/contests/icpc-gwalior-pune-2020-regional-round) - Date & Time — 18 August 2021, Wednesday, 18:00 IST - Duration — **4 Hours** - There is a ranklist freeze of 60 minutes. Ranklist will freeze at 21:00 IST. - There will be 10-13 questions to solve - Will follow standard ICPC scoring system (20 minutes penalty and 1 point per problem) - The problems may not be sorted by difficulty **Selection Criteria** - Top *few* teams will advance to World Finals <spoiler summary="Spoiler"> ![ ](https://i.kym-cdn.com/photos/images/newsfeed/001/462/400/978.jpg) </spoiler> **Clarifications** - Only ask the clarifications about the problems by messaging the [private clarification group via discuss](https://discuss.codedrills.io/g/clarifications). - Do not a...
We recommend you to read the statements of all problems. Good luck & Have fun! May the best bugaboo

Full text and comments »

  • Vote: I like it
  • +338
  • Vote: I do not like it

208.
IndiaHacks Finals — rated CF round
By Errichto, 10 years ago, In English
IndiaHacks Finals — rated CF round Hi everybody. The IndiaHacks finals will take place tomorrow (on Saturday). The contest is being organized by HackerEarth. Just after the official finals, the CF round will start ([check-your-time](http://timeanddate.com/worldclock/fixedtime.html?day=19&month=3&year=2016&hour=11&min=35&sec=0&p1=166)) with almost the same problems. <s>You can treat it as a standard CF round &mdash; there will be 5 problems in each of 2 divisions, and 2 hours to solve them.</s> Two divisions will compete together on the problem set with 7 problems, with 2 hours to solve them. I want to especially thank [user:I_love_Tanya_Romanova,2016-03-18] for testing the problems, [user:GlebsHP,2016-03-18] for help with making the CF round possible, and [user:MikeMirzayanov,2016-03-18] for his awesome attitude and for the Polygon system. Setters: [user:lewin,2016-03-18], [user:k790alex,2016-03-18], [user:Sokolov,2016-03-18], [user:Errichto,2016-03-18]. Testers: [user:I_love_Tanya_Romanova,2016-03-18], [use...
I wish you great fun and no frustrating bugs. Enjoy the contest.

Full text and comments »

  • Vote: I like it
  • +197
  • Vote: I do not like it

209.
ICPC Baku World Finals Alumni Event: I invite you to a push-up challenge!
By MikeMirzayanov, 12 months ago, In English
ICPC Baku World Finals Alumni Event: I invite you to a push-up challenge! <div style="float:right; margin: 0 1em 1em 1em; width:200px;"> <img src="/predownloaded/1f/73/1f7347fb7cecd54d17063bfda097a75f214cfa56.jpg"/> <br> <small class="muted"><center>The image was created with the help of OpenAI, a sponsor of the ICPC World Finals 2025.</center></small> </div> Hello, Codeforces. Today I arrived in Baku for the ICPC World Finals. The very first participant I met asked me if we would be doing push-ups. Yes! This year I decided to repeat the fun event and I invite you to join the push-up challenge. It will take place on <a href="https://www.timeanddate.com/worldclock/fixedtime.html?day=3&month=9&year=2025&hour=17&min=00&sec=0&p1=166">September 3rd at 18:00</a>. The best performer will receive a prize from Codeforces! And everyone in the top 25 will get a souvenir. If you're not ready to do push-ups, come anyway to cheer for your friends and have fun! We'll repeat last year's format: push-ups in rounds of 25. Gradually, people will start droppi...
If you're not ready to do push-ups, come anyway to cheer for your friends and havefun!

Full text and comments »

  • Vote: I like it
  • +615
  • Vote: I do not like it

210.
Codeforces Wrapped 2022 — Share your yearly statistics!
By awoo, 4 years ago, In English
Codeforces Wrapped 2022 — Share your yearly statistics! Feliz Navidad, Codeforces! I'm a huge data nerd and an avid Codeforces user. I decided to combine these traits and make a service to provide everyone with some sort of their yearly statistics on this wonderful site in a neat form. My main goals were to make a report card that: - contains insighful statistics; - is not overloaded with information; - is easy to share. In persuit of that, I discarded multiple stats which were too boring, took too much space <s>or were hard to implement within the limitations of CF API</s>. I find the final choice of data really fun. I hope you like the result too! The service is pretty intuitive to use. Enter your handle (in case you changed it, enter the one you had throughout the year), get the report card and share it with the world by clicking "open as image". <spoiler summary="Disclaimer"> I'm not a professional web-designer, neither I'm at least an experienced one. Thanks to my friends from kbr discord server, I managed to fix ...
were hard to implement within the limitations of CF API. I find the final choice of data reallyfun

Full text and comments »

  • Vote: I like it
  • +559
  • Vote: I do not like it

211.
Educational Codeforces Round 102 Editorial
By awoo, history, 6 years ago, translation, In English
Educational Codeforces Round 102 Editorial [problem:1473A] Idea: [user:BledDest,2021-01-15], [user:adedalic,2021-01-15] <spoiler summary="Tutorial"> [tutorial:1473A] </spoiler> <spoiler summary="Solution (Neon)"> ~~~~~ #include <bits/stdc++.h> using namespace std; int main() { int tc; cin >> tc; while (tc--) { int n, d; cin >> n >> d; vector<int> a(n); for (int& x : a) cin >> x; sort(a.begin(), a.end()); cout << (a.back() <= d || a[0] + a[1] <= d ? "YES" : "NO") << endl; } } ~~~~~ </spoiler> [problem:1473B] Idea: [user:BledDest,2021-01-15] <spoiler summary="Tutorial"> [tutorial:1473B] </spoiler> <spoiler summary="Solution (Neon)"> ~~~~~ #include <bits/stdc++.h> using namespace std; int main() { auto mul = [](string s, int k) -> string { string res = ""; while (k--) res += s; return res; }; int tc; cin >> tc; while (tc--) { string s, t; cin >> s >> t; int n = s.length(), m = t.length(); ...
~~~~~ fun main() { repeat(readLine()!!.toInt()) { val (n, k) = readLine()!!.split

Full text and comments »

  • Vote: I like it
  • +133
  • Vote: I do not like it

212.
Kotlin Heroes 13 Editorial
By BledDest, 12 months ago, In English
Kotlin Heroes 13 Editorial I hope you liked the problems! Thank you for participation. I am sorry that the difference between H and I turned out to be that big, I didn't expect that so many people would solve H. The contest was prepared by me, [user:Neon,2025-09-13], [user:adedalic,2025-09-13], [user:FelixArg,2025-09-13] and [user:Roms,2025-09-13]. I would like to express my gratitude to the testers who helped us improve the contest: [user:pashka,2025-09-13], [user:shnirelman,2025-09-13] and [user:awoo,2025-09-13]. See you in the next episode of Kotlin Heroes... sometime in the future (probably near the end of 2025). [problem:2141A] Idea: [user:BledDest,2025-09-13], preparation: [user:Neon,2025-09-13] <spoiler summary="Tutorial"> [tutorial:2141A] </spoiler> <spoiler summary="Solution (Neon)"> ~~~~~ fun main() = repeat(readln().toInt()) { val n = readln().toInt() val a = readln().split(" ").map { it.toInt() } val p = a.runningReduce { x, y -> minOf(x, y) } val ans = (1..n).filt...
)"> ~~~~~ fun main() = repeat(readln().toInt()) { val n = readln().toInt() val a = readln, > ~~~~~ fun main() = repeat(readln().toInt()) { val n = readln, private fun intarr(sz: Int, v: Int = 0) = IntArray(sz) { v } private fun longarr(sz: Int, v: Long, private fun readInt() = read().toInt() private fun readLong() = read().toLong() privatefun

Full text and comments »

  • Vote: I like it
  • +48
  • Vote: I do not like it

213.
THE OPTIMAL PRACTICE STRATEGY (**NOT CLICKBAIT**)
By galen_colin, 2 years ago, In English
THE OPTIMAL PRACTICE STRATEGY (**NOT CLICKBAIT**) Spoiler: it's clickbait. Sorry. Titles like those are fun. ...but, it's the same style of clickbait as my [roadmap](https://www.youtube.com/watch?v=bSdp2WeyuJY) [spoiler 2: if you haven't seen that, it markets itself as a standard roadmap (y'know, soulless and devoid of purpose), but then a few minutes in, says "ok but roadmaps are stupid and here's the advice that you really need" and completely changes the direction of the video]. That's my style of clickbait, and that's the vibe this blog goes for. [cut] <br><br> So... hear me out, please. The start ------------------ First, a couple meta-notes. I will likely exaggerate my tone a bit here for dramatic effect. Don't take it personally, please. Also, **this applies to almost all ratings**. At the very least, I recommend you process the main point of this blog and see whether or not you already do something similar (for most people... probably not?) The problem ------------------ I'm sure if you've looked at the...
Spoiler: it's clickbait. Sorry. Titles like those are fun.

Full text and comments »

Tags hi
  • Vote: I like it
  • +207
  • Vote: I do not like it

214.
[CONTEST OVER] MIT Informatics Tournament 2024 Spring Invitational
By antontrygubO_o, 2 years ago, In English
[CONTEST OVER] MIT Informatics Tournament 2024 Spring Invitational **Update 2**: The Qualification Round has **officially concluded**! A huge thank you to our contestants for joining us and supporting this new initiative! Congratulations to the top 16 finalists who are advancing to the finals round (along with many more as we continue to confirm people's availability)! 1. [user:Rewinding,2024-04-24] 2. [user:ksun48,2024-04-24] 3. [user:Petr,2024-04-24] 4. [user:Geothermal,2024-04-24] 5. [user:mango_lassi,2024-04-24] 6. [user:hank55663,2024-04-24] 7. [user:ecnerwala,2024-04-24] 8. [user:MiFaFaOvO,2024-04-24] 9. [user:Kevin114514,2024-04-30] 10. [user:A_G,2024-04-30] 11. [user:Adam_GS,2024-04-24] 12. [user:Tourist,2024-04-24] 13. [user:FlowerOfSorrow,2024-04-24] 14. Matthew Allan 15. [user:uwu,2024-04-24] 16. [user:TLE,2024-04-24] At this time, the scoreboard has been finalized, and you can upsolve our problems / watch our video tutorials with the following links: - Finalized Scoreboard: [https://mitit.org/Contest/ViewScoreboar...
Round is filled with exciting activities, such as fun tours around Boston, a fancy banquet

Full text and comments »

  • Vote: I like it
  • +320
  • Vote: I do not like it

215.
Codeforces Round 1096 (Div. 3)
By yse, 4 months ago, In English
Codeforces Round 1096 (Div. 3) Hello, Codeforces! ------------------ I am super excited to invite you to participate in [contest:2227], which will take place on [contest_time:2227]. You will be given $2$ hours and $30$ minutes to solve $8$ problems. All problems were authored and prepared by me. The round will be hosted by rules of educational rounds (extended ICPC). Thus, all solutions will be judged on preliminary tests during the round, and after the round, there will be a 12-hour phase of **open hacks**. After the open hack phase, all accepted solutions will be rejudged on successful hacks. Also, note that there is no score distribution but the usual penalty of **10 minutes** for each wrong submission, following the rules of educational rounds. [Remember](https://codeforces.me/blog/entry/59228) that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsporting behavior. To qualify as...
Good luck, and most importantly, have fun!

Full text and comments »

  • Vote: I like it
  • +291
  • Vote: I do not like it

216.
April Fools Day Contest 2021 — ZS Edition
By zscoder, history, 5 years ago, In English
April Fools Day Contest 2021 — ZS Edition Hi everyone, April Fools is near and as usual we have an [April Fools Day Contest](https://codeforces.me/blog/entry/88840) on Codeforces this year. In addition to that, I usually try to host some form of mini April Fools Contest for my friends every year (or almost every year). This year, I am trying to host a bigger April Fools Day contest than usual and I invite everyone to participate! In view of the April Fools contest on Codeforces, the round will begin at [31 March 10pm (GMT+8)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=April+Fools+Day+Contest+2021+%28ZS%29&iso=20210331T22&p1=122) and lasts for exactly $24$ hours (and thus it will end ~35 minutes before the CF April Fools round). The contest will consist of several unusual tasks, and I hope that everyone will at least find something interesting. The problems will not be sorted by increasing order of difficulty (if the word difficulty is even applicable), so it is **highly advisable** to read (and try!)...
**UPD 3:** The contest has just begun! Good luck and have fun. :)

Full text and comments »

  • Vote: I like it
  • +247
  • Vote: I do not like it

217.
Codeforces Round #563 (Div. 2)
By mohammedehab2002, 7 years ago, In English
Codeforces Round #563 (Div. 2) Hi! I'm back with not one, not two, but three contests, although I have no promises about when to expect them.... The first of them, codeforces round #563, will take place on [contest_time:1174]. It's rated for the second division, but, as usual, first division participants can take part out of competition. I'm the problemsetter of the round. I'd like to thank [user:KAN,2019-06-01] for coordinating the round (and his patience .. try coordinating ~20 problems), [user:arsijo,2019-06-02] for helping with the preparation, [user:Um_nik,2019-06-01], [user:opukittpceno_hhr,2019-06-02], [user:Aleks5d,2019-06-02], [user:Rifai,2019-06-03], [user:pllk,2019-06-03], [user:ulna,2019-06-03], [user:Ivan19981305,2019-06-03], and [user:PrianishnikovaRina,2019-06-03] for testing the round, and [user:MikeMirzayanov,2019-06-01] for the great codeforces and polygon platforms. In this round, you'll be given 6 problems and 2 hours to solve them. **UPD:** I decided to drop the 3 seconds rule. Th...
Good luck & Have fun!

Full text and comments »

  • Vote: I like it
  • +466
  • Vote: I do not like it

218.
Educational Codeforces Round 143 Editorial
By awoo, history, 4 years ago, In English
Educational Codeforces Round 143 Editorial [problem:1795A] Idea: [user:BledDest,2023-02-17] <spoiler summary="Tutorial"> [tutorial:1795A] </spoiler> <spoiler summary="Solution (Neon) 1"> ~~~~~ #include <bits/stdc++.h> using namespace std; int main() { auto ok = [](string s) { for (int i = 1; i < (int)s.size(); ++i) if (s[i - 1] == s[i]) return false; return true; }; int t; cin >> t; while (t--) { int n, m; string s, t; cin >> n >> m >> s >> t; bool f = false; for (int x = 0; x < 2; ++x) { string cs = s, ct = t; for (int i = 0; i < n; ++i) { f |= ok(cs) && ok(ct); ct.push_back(cs.back()); cs.pop_back(); } swap(n, m); swap(s, t); } cout << (f ? "YES\n" : "NO\n"); } } ~~~~~ </spoiler> <spoiler summary="Solution (Neon) 2"> ~~~~~ #include <bits/stdc++.h> using namespace std; int main() { int t; cin >> t; while (t--) { int n, m; string ...
fun main() { repeat(readln().toInt()) { val n = readln().toInt() var h

Full text and comments »

  • Vote: I like it
  • +121
  • Vote: I do not like it

219.
CodeTON Round 1 (Div. 1 + Div. 2, Rated, Prizes!)
By FelixMP, history, 4 years ago, In English
CodeTON Round 1 (Div. 1 + Div. 2, Rated, Prizes!) Hello! It is a pleasure to invite you to [contest:1656]! The round will take place on [contest_time:1656]. The round will be **rated** for all participants. The problems of the round were authored by [user:FelixMP,2022-03-20], and they were prepared by [user:FelixMP,2022-03-20] and [user:xpov1LL,2022-03-20]. I would like to thank the following people: - [user:Baqtraqking,2022-03-20] for having the idea of preparing a Codeforces Round and helping with the solution to one problem; [user:Baqtraqking,2022-03-20], [user:izanbf,2022-03-20] and [user:xpov1LL,2022-03-20] for early help and discussion of problems, and [user:Baqtraqking,2022-03-20], [user:xpov1LL,2022-03-20] and [user:OneStone,2022-03-20] for proposals that did not make it to the final problem set. - [user:74TrAkToR,2022-03-20] for coordination of the round. - [user:MikeMirzayanov,2022-03-20] for the great platforms Codeforces and Polygon. - [user:Um_nik,2022-03-20], [user:Monogon,2022-03-24], [user:AlexLuchianov...
- 3000 - 3250 - 3750 - 4500$. Hope you have fun!

Full text and comments »

  • Vote: I like it
  • +404
  • Vote: I do not like it

220.
Educational Codeforces Round 87 Editorial
By awoo, history, 6 years ago, translation, In English
Educational Codeforces Round 87 Editorial [problem:1354A] Idea: [user:BledDest,2020-05-18] <spoiler summary="Tutorial"> [tutorial:1354A] </spoiler> <spoiler summary="Solution (pikmike)"> ~~~~~ t = int(input()) for _ in range(t): a, b, c, d = map(int, input().split()) if b >= a: print(b) continue if c <= d: print(-1) continue a -= b dif = c - d print(b + (a + dif - 1) // dif * c) ~~~~~ </spoiler> [problem:1354B] Idea: [user:BledDest,2020-05-18] <spoiler summary="Tutorial"> [tutorial:1354B] </spoiler> <spoiler summary="Solution (BledDest)"> ~~~~~ #include<bits/stdc++.h> using namespace std; char buf[200043]; int main() { int t; scanf("%d", &t); for(int i = 0; i < t; i++) { scanf("%s", buf); string s = buf; int ans = int(1e9); int n = s.size(); vector<pair<char, int> > c; for(auto x : s) { if(c.empty() || c.back().first != x) c.push_back(make_pair(x, 1)); else c.back().second++; } int m = c.size(); for...
fun main() { val PI = acos(-1.0) val T = readLine()!!.toInt() for (tc in 1..T

Full text and comments »

  • Vote: I like it
  • +267
  • Vote: I do not like it

221.
SNWS 2022 streams
By tourist, 5 years ago, In English
SNWS 2022 streams Tune in at [twitch.tv/the__tourist](https://twitch.tv/the__tourist) at around [22:30 MSK, 11 Jan 2022](https://www.timeanddate.com/worldclock/fixedtime.html?msg=touristream:+SNWS+R1&iso=20220111T2230&p1=3396) to watch me solving [SnarkNews Winter Series 2022 Round 1](https://contest.yandex.com/snws2022/contest/23957/enter) live! First I will do the round competitively without much interaction, and I'll be up for discussing the problems on stream afterwards. SnarkNews Winter/Summer Series (SNWS/SNSS) is organized by [user:snarknews,2022-01-11] and consists of 5 rounds. Each round is a virtual 6-problem 80-minute contest open for 10 days. The series is open to all, but problem statements are in Russian only. On stream, I'll read the problem statements automatically translated to English. To make the stream more fun and for easier understanding of what will be going on, you're welcome to do the round yourself beforehand! If you don't understand Russian, you can also compete using au...
To make the stream more fun and for easier understanding of what will be going on, you're welcome

Full text and comments »

  • Vote: I like it
  • +243
  • Vote: I do not like it

222.
Educational Codeforces Round 92 Editorial
By awoo, history, 6 years ago, translation, In English
Educational Codeforces Round 92 Editorial [problem:1389A] Idea: [user:BledDest,2020-07-30] <spoiler summary="Tutorial"> [tutorial:1389A] </spoiler> <spoiler summary="Solution (BledDest)"> ~~~~~ t = int(input()) for i in range(t): l, r = map(int, input().split()) if l * 2 > r: print(-1, -1) else: print(l, l * 2) ~~~~~ </spoiler> [problem:1389B] Idea: [user:Roms,2020-07-30] <spoiler summary="Tutorial"> [tutorial:1389B] </spoiler> <spoiler summary="Solution 1 (pikmike)"> ~~~~~ for _ in range(int(input())): n, k, z = map(int, input().split()) a = [int(x) for x in input().split()] ans = 0 s = 0 mx = 0 for t in range(z + 1): pos = k - 2 * t if pos < 0: continue mx = 0 s = 0 for i in range(pos + 1): if i < n - 1: mx = max(mx, a[i] + a[i + 1]) s += a[i] ans = max(ans, s + mx * t) print(ans) ~~~~~ </spoiler> <spoiler summary="Solution 2 (pikmike)"> ~~~~~ for _ in range(int(input())): n, k, z = map(int, ...
fun main() { repeat(readLine()!!.toInt()) { val (n, k) = readLine()!!.split(' ').map, ~~~~~ fun gcd(a: Long, b: Long): Long { if (a == 0L) return b return gcd(b % a, a) }

Full text and comments »

  • Vote: I like it
  • +127
  • Vote: I do not like it

223.
The 4th Universal Cup Announcement
By Qingyu, 11 months ago, In English
The 4th Universal Cup Announcement Hi, The 4th Universal Cup has officially begun! For those who are new: the Universal Cup is a weekly, open team contest in the ICPC format, featuring global problem sets. In the previous season, more than 1,000 teams from over 500 institutions worldwide registered and took part in 40 stages, covering contests from Asia, Europe, and the Americas. Our participants range from former ICPC and IOI champions to current students sharpening their skills. We are dedicated to offering training resources for competitive programming teams and building a platform where the world's top talents can showcase their abilities. [Join us](https://contest.ucup.ac/register) today, you will be able to compete with teams from around the world, access a rich archive of past high-quality contests for training, and connect with others on our server to share knowledge and tips. For our friends from the past seasons, we've made several major updates, from the [rules](https://ucup.ac/rule/) to our [cont...
We cannot wait to see you in the contests. Good luck, and have fun!

Full text and comments »

  • Vote: I like it
  • +411
  • Vote: I do not like it

224.
Educational Codeforces Round 89 Editorial
By awoo, history, 6 years ago, translation, In English
Educational Codeforces Round 89 Editorial [problem:1366A] Idea: [user:Roms,2020-06-12] <spoiler summary="Tutorial"> [tutorial:1366A] </spoiler> <spoiler summary="Solution (Roms)"> ~~~~~ for _ in range(int(input())): l, r = map(int, input().split()) print(min(l, r, (l + r) // 3)) ~~~~~ </spoiler> [problem:1366B] Idea: [user:Roms,2020-06-12] <spoiler summary="Tutorial"> [tutorial:1366B] </spoiler> <spoiler summary="Solution (Roms)"> ~~~~~ for _ in range(int(input())): n, x, m = map(int, input().split()) l, r = x, x for _ in range(m): L, R = map(int, input().split()) if max(l, L) <= min(r, R): l = min(l, L) r = max(r, R) print(r - l + 1) ~~~~~ </spoiler> [problem:1366C] Idea: [user:BledDest,2020-06-12] <spoiler summary="Tutorial"> [tutorial:1366C] </spoiler> <spoiler summary="Solution (BledDest)"> ~~~~~ #include <bits/stdc++.h> using namespace std; void solve() { int n, m; ...
~~~~~ fun main() { val n = readLine()!!.toInt() val a = readLine()!!.split(' ').map

Full text and comments »

  • Vote: I like it
  • +113
  • Vote: I do not like it

225.
Teza Round 1 (Codeforces Round 1015, Div. 1 + Div. 2)
By zltzlt, history, 17 months ago, In English
Teza Round 1 (Codeforces Round 1015, Div. 1 + Div. 2) Hi, Codeforces! We are pleased to invite you to [Teza Round 1 (Codeforces Round 1015, Div. 1 + Div. 2)](https://codeforces.me/contests/2084), which will be held on [contest_time:2084] The problems are authored and prepared by [user: CharlieV, 2025-3-27] and me. You will be given **8 problems**, one of which is divided into two subtasks, and **3 hours** to solve them. **The round will be rated for everyone.** I would like to thank everyone who has helped prepare for this round: - [user: Sugar_fan, 2025-3-27] for his excellent coordination. - [user: Alexdat2000, 2025-3-27] for the Russian translation. - [user: CharlieV, 2025-3-27], [user: ExplodingKonjac, 2025-3-27], [user: QwQwf, 2025-3-27], [user: sinsop90, 2025-3-27] for providing problem ideas despite a few unused. - [user: 244mhq, 2025-3-27] for reviewing some of the problems when coordinating my previous rounds. - [user: jqdai0815, 2025-3-27], [user: StarSilk, 2025-3-27], [user: 244mhq, 2025-3-27], [user: N_z__, 20...
Good luck, have fun!

Full text and comments »

  • Vote: I like it
  • +200
  • Vote: I do not like it

226.
Educational Codeforces Round 70 Editorial
By awoo, history, 7 years ago, translation, In English
Educational Codeforces Round 70 Editorial [problem:1202A] Idea: [user:adedalic,2019-08-08] <spoiler summary="Tutorial"> [tutorial:1202A] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ fun main(args: Array<String>) { val T = readLine()!!.toInt() for (tc in 1..T) { val x = readLine()!!.reversed() val y = readLine()!!.reversed() val posY = y.indexOf('1') val posX = x.indexOf('1', posY) println(posX - posY) } } ~~~~~ </spoiler> [problem:1202B] Idea: [user:adedalic,2019-08-08] <spoiler summary="Tutorial"> [tutorial:1202B] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ const val INF = 1e9.toInt() fun main(args: Array<String>) { val s = readLine()!!.map { it - '0' } val cf = Array(10) {Array(10) {0}} for (i in 1 until s.size) cf[s[i - 1]][s[i]]++ for (x in 0..9) { for (y in 0..9) { val ds = Array(10) {Array(10) {INF + 7}} for (v in 0..9) { ...
fun main(args: Array) { val T = readLine()!!.toInt() for (tc in 1..T, fun main(args: Array) { val s = readLine()!!.map { it - '0' } val cf = Array(10

Full text and comments »

  • Vote: I like it
  • +187
  • Vote: I do not like it

227.
Educational Codeforces Round 94 Editorial
By awoo, history, 6 years ago, translation, In English
Educational Codeforces Round 94 Editorial [problem:1400A] Idea: [user:BledDest,2020-08-26] <spoiler summary="Tutorial"> [tutorial:1400A] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ fun main() { repeat(readLine()!!.toInt()) { val n = readLine()!!.toInt() val c = readLine()!!.groupingBy { it }.eachCount().maxBy { it.value }!!.key println(c.toString().repeat(n)) } } ~~~~~ </spoiler> [problem:1400B] Idea: [user:adedalic,2020-08-26] <spoiler summary="Tutorial"> [tutorial:1400B] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ fun main() { repeat(readLine()!!.toInt()) { val (p, f) = readLine()!!.split(' ').map { it.toInt() } var (cntS, cntW) = readLine()!!.split(' ').map { it.toInt() } var (s, w) = readLine()!!.split(' ').map { it.toInt() } if (s > w) { s = w.also { w = s } cntS = cntW.also { cntW = cntS } } var ans = 0 for (s1 in 0.....
~~~~~ fun main() { repeat(readLine()!!.toInt()) { val (p, f) = readLine()!!.split, ~~~~~ fun main() { repeat(readLine()!!.toInt()) { val n = readLine()!!.toInt

Full text and comments »

  • Vote: I like it
  • +204
  • Vote: I do not like it

228.
Codeforces Round #977 (Div. 2, based on COMPFEST 16 — Final Round)
By ArvinCiu, 23 months ago, In English
Codeforces Round #977 (Div. 2, based on COMPFEST 16 — Final Round) <img alt="logo" src="/predownloaded/7c/c9/7cc971d2212c2990000eca9584691770d4e6bc38.png" style="float: right;height: 100.0px;margin: 10.0px;max-width: 100.0%;max-height: 100.0%;"> Halo, **Codeforces**! Ape kabar kitak? Nyi deu sit bau maang? &#128525; &#128525; COMPFEST 16 is happy to invite you to participate in [contest:2021] on [contest_time:2021]. The round will be **rated**. You will be given **2 hours** to solve **5 problems, 2 of them will have subtasks**. **Note the unusual time of the round**. ------------------ The problems are written by [user:ArvinCiu,2024-10-05], [user:CyberSleeper,2024-10-05], [user:athin,2024-10-05], and [user:joelgun14,2024-10-05]. We would like to thank: - [user:KAN,2024-10-05] for helping to host the round; - [user:errorgorn,2024-10-05] for the based coordination; - [user:gansixeneh,2024-10-05], [user:CyberSleeper,2024-10-05], [user:joelgun14,2024-10-05], and [user:icebear30,2024-10-05] for helping with the problem preparation; ...
We hope you will enjoy and have fun in the contest. Muga-muga beja lan isa entuk biji apik

Full text and comments »

  • Vote: I like it
  • +384
  • Vote: I do not like it

229.
Codeforces Beta Round #80
By Alex_KPR, 15 years ago, translation, In English
Codeforces Beta Round #80 <p>Hi all!</p><p>Now it's time for 80th Codeforces Beta Round.</p><p>The authors of the contest are:&nbsp;<span class="Apple-style-span" style="font-family: verdana, arial, sans-serif; font-size: 12px; "><a href="http://codeforces.me/profile/Alex_KPR" title="Подполковник Alex_KPR" class="rated-user user-red" style="font-family: arial; text-decoration: none !important; font-weight: bold; color: rgb(0, 0, 204); ">Alex_KPR</a></span>,&nbsp;<span class="Apple-style-span" style="font-family: verdana, arial, sans-serif; font-size: 12px;"><a href="http://codeforces.me/profile/winger" title="Подполковник winger" class="rated-user user-red" style="font-family: arial; text-decoration: none !important; font-weight: bold; color: rgb(0, 0, 204); ">winger</a></span>,&nbsp;<span class="Apple-style-span" style="font-family: verdana, arial, sans-serif; font-size: 12px;"><a href="http://codeforces.me/profile/RAD" title="Штаб, RAD" class="rated-user user-admin" style="font-family: arial; text-decoration:...
Good luck and have fun! _____________________________________

Full text and comments »

  • Vote: I like it
  • +208
  • Vote: I do not like it

230.
Codeforces Round #765. One of the contest authors is entertaining again.
By Wind_Eagle, 5 years ago, translation, In English
Codeforces Round #765. One of the contest authors is entertaining again. Hello, Codeforces! Codeforces #765 (Div. 2) took place not so long ago, and one of its authors was me. When an hour had passed since the contest started, I decided to remember the old days and start making fun of the cheaters. To that end, I decided to take a look at the old cheater groups and see how they were doing. The first group I looked into &mdash; is the group where the admin is actively fighting against cheaters. So, there really weren't any cheaters on the round. I think that's a success. The second group I checked out &mdash; it's a group with 2.5k users. I decided that just going in there would be too boring, so I decided to write there that I was a contest author. Here's the reaction of the users: <spoiler summary="Picture"> <a href="https://imgbb.com/"><img src="https://i.ibb.co/0Xt07qt/Screenshot-20220112-164100.png" alt="pic1" border="0"></a> </spoiler> Can you imagine?! I write that I am the author of the contest, and I am offered to leak the solution ...
making fun of the cheaters.

Full text and comments »

  • Vote: I like it
  • +423
  • Vote: I do not like it

231.
Educational Codeforces Round 101 Editorial
By awoo, history, 6 years ago, translation, In English
Educational Codeforces Round 101 Editorial [problem:1469A] Idea: [user:BledDest,2020-12-29] <spoiler summary="Tutorial"> [tutorial:1469A] </spoiler> <spoiler summary="Solution 1 (BledDest)"> ~~~~~ t = int(input()) for i in range(t): s = input() if len(s) % 2 == 0 and s[0] != ')' and s[-1] != '(': print('YES') else: print('NO') ~~~~~ </spoiler> <spoiler summary="Solution 2 (BledDest)"> ~~~~~ t = int(input()) for i in range(t): s = input() n = len(s) a = [s[i] for i in range(n)] cnt = n // 2 - 1 for j in range(n): if a[j] == '?': if cnt > 0: cnt -= 1 a[j] = '(' else: a[j] = ')' bal = 0 minbal = 0 for j in range(n): if a[j] == '(': bal += 1 else: bal -= 1 minbal = min(bal, minbal) print('YES' if bal == 0 and minbal >= 0 else 'NO') ~~~~~ </spoiler> [problem:1469B] Idea: [user:Bled...
~~~~~ fun main() { repeat(readLine()!!.toInt()) { val (n, k) = readLine()!!.split

Full text and comments »

  • Vote: I like it
  • +121
  • Vote: I do not like it

232.
Codeforces Round #744 (Div. 3)
By doreshnikov, history, 5 years ago, translation, In English
Codeforces Round #744 (Div. 3) Hello Codeforces! Sorry for a bit delayed English announcement, we are glad to invite you all to [contest:1579], third division round held on [contest_time:1579]. This round was prepared by me and [user:MikeMirzayanov,2021-09-26] and we hope that you'll find the problems interesting and enjoy solving them. I would like to thank [user:MikeMirzayanov,2021-09-26] for helping me with both writing and preparing the problems for this round. Since it's the second Div. 3 round held I'm involved in but only the first one I'm preparing problems for from zero all the way to the end, without his guidance it would've taken much more of my time. Also special thanks to [user:nizamoff,2021-09-28], [user:andreumat,2021-09-28], [user:QAZZY,2021-09-28], [user:Vladosiya,2021-09-28], [user:CtrlAlt,2021-09-28], [user:vladmart,2021-09-28], [user:Igorjan94,2021-09-28], [user:okwedook,2021-09-28], [user:I_Remember_Olya_ashmelev,2021-09-28] and [user:Aris_244_,2021-09-28] for testing the round and givi...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +308
  • Vote: I do not like it

233.
A serious proposal for Division 1.5
By drastogi21, 6 years ago, In English
A serious proposal for Division 1.5 Hi Codeforces Community, Are you rated 2100 or higher? If yes, then it must be frustrating waiting for rated contests. I thus, bring to you a serious (not troll) proposal for Div 1.5 contests and some small changes in contest setups. Note that, I have also prepared a contest and know very well how hard it is to come up with interesting and novel ideas, so this is by no means a blog where I'm just criticizing setters that they are not setting frequent contests. _Why Division 1.5?_ The frequency of Div. 1's is extremely low is compared to Div. 2. Moreover, coming up with the last problem of a Div. 1 round is extremely hard. If you have got good enough ideas (up to let's say Div 1 D), you still get to make the contest! _How does it benefit the contestants?_ Well, more contests are always fun! _How does it benefit the setters?_ Read the answer to the 1st question. _Rated Range?_ Let's make it rated for up to 2600. _But you know, anyone will become red, blah bl...
Well, more contests are always fun!

Full text and comments »

  • Vote: I like it
  • +637
  • Vote: I do not like it

234.
Educational Codeforces Round 106 Editorial
By awoo, history, 5 years ago, translation, In English
Educational Codeforces Round 106 Editorial [problem:1499A] Idea: [user:adedalic,2021-03-19] <spoiler summary="Tutorial"> [tutorial:1499A] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ fun main() { repeat(readLine()!!.toInt()) { val (n, k1, k2) = readLine()!!.split(' ').map { it.toInt() } val (w, b) = readLine()!!.split(' ').map { it.toInt() } if (k1 + k2 >= 2 * w && (n - k1) + (n - k2) >= 2 * b) println("YES") else println("NO") } } ~~~~~ </spoiler> [problem:1499B] Idea: [user:BledDest,2021-03-19] <spoiler summary="Tutorial"> [tutorial:1499B] </spoiler> <spoiler summary="Solution (Neon)"> ~~~~~ #include <bits/stdc++.h> using namespace std; int main() { int t; cin >> t; while (t--) { string s; cin >> s; int i = s.find("11"); int j = s.rfind("00"); cout << (i != -1 && j != -1 && i < j ? "NO" : "YES") << endl; } } ~~~~~ </spoiler> [problem:1499C] Idea: [use...
~~~~~ fun main() { repeat(readLine()!!.toInt()) { val (n, k1, k2) = readLine, ~~~~~ fun main() { repeat(readLine()!!.toInt()) { val n = readLine()!!.toInt

Full text and comments »

  • Vote: I like it
  • +111
  • Vote: I do not like it

235.
Educational Codeforces Round 86 Editorial
By awoo, history, 6 years ago, translation, In English
Educational Codeforces Round 86 Editorial [problem:1342A] Idea: [user:BledDest,2020-04-27] and [user:adedalic,2020-04-27] <spoiler summary="Tutorial"> [tutorial:1342A] </spoiler> <spoiler summary="Solution (Roms)"> ~~~~~ for _ in range(int(input())): x, y = map(int, input().split()) a, b = map(int, input().split()) b = min(b, a + a) if x < y: x, y= y, x print(y * b + (x - y) * a) ~~~~~ </spoiler> [problem:1342B] Idea: [user:adedalic,2020-04-27] <spoiler summary="Tutorial"> [tutorial:1342B] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ fun main() { val T = readLine()!!.toInt() for (tc in 1..T) { val t = readLine()!! val s = t.toCharArray().distinct().joinToString("").repeat(t.length) println(s) } } ~~~~~ </spoiler> [problem:1342C] Idea: [user:BledDest,2020-04-27] and [user:adedalic,2020-04-27] <spoiler summary="Tutorial"> [tutorial:1342C] </spoiler> <spoiler summary="Solution (Bled...
~~~~~ fun main() { val T = readLine()!!.toInt() for (tc in 1..T) { val t

Full text and comments »

  • Vote: I like it
  • +149
  • Vote: I do not like it

236.
Educational Codeforces Round 168 Editorial
By awoo, history, 2 years ago, translation, In English
Educational Codeforces Round 168 Editorial [problem:1997A] Idea: [user:BledDest,2024-07-31] <spoiler summary="Tutorial"> [tutorial:1997A] </spoiler> <spoiler summary="Solution (BledDest)"> ~~~~~ #include<bits/stdc++.h> using namespace std; void solve() { string s; cin >> s; int n = s.size(); int idx = -1; for(int i = 0; i + 1 < n; i++) if(s[i] == s[i + 1]) idx = i; if(idx == -1) { if(s.back() == 'a') cout << (s + "b") << endl; else cout << (s + "a") << endl; } else { string t = "a"; if(s[idx] == 'a') t = "b"; cout << s.substr(0, idx + 1) + t + s.substr(idx + 1) << endl; } } int main() { int t; cin >> t; for(int i = 0; i < t; i++) solve(); } ~~~~~ </spoiler> [problem:1997B] Idea: [user:BledDest,2024-07-31] <spoiler summary="Tutorial"> [tutorial:1997B] </spoiler> <spoiler summary="Solution (Neon)"> ~~~~~ #include <bits/stdc++.h> using namespace std; int main() { int t; cin >> t; while (t--) { int n; ...
fun main() { repeat(readln().toInt()) { val n = readln().toInt() val s

Full text and comments »

  • Vote: I like it
  • +89
  • Vote: I do not like it

237.
Codeforces Round #439 (Div. 2)
By Tommyr7, history, 9 years ago, In English
Codeforces Round #439 (Div. 2) Hi, Codeforces! I'm quite excited to invite you to Codeforces Round #439 (Div. 2) which takes place at [16:35 MSK on 6 October](https://www.timeanddate.com/worldclock/fixedtime.html?day=06&month=10&year=2017&hour=16&min=35&sec=0&p1=166) and lasts for two hours. One of the five problems is created by [user:quailty,2017-10-05], and the others are created by me. This is our first round here. The round couldn't have been realized without efforts of [user:KAN,2017-10-05] and [user:gritukan,2017-10-05]. Besides, I also want to say thanks to our testers: [user:cyand1317,2017-10-05], [user:visitWorld,2017-10-05], [user:Nisiyama_Suzune,2017-10-05], [user:cdkrot,2017-10-05] and [user:gainullin.ildar,2017-10-05]. Thanks for your help to the contest. Also, thanks to [user:MikeMirzayanov,2017-10-05] with the fantastic Codeforces and Polygon platforms. The contest will consist of five problems and it is **rated** for Div. 2 contestants. The same as before, Div. 1 contestants can take pa...
Have fun! See you next time! (Let's wait and see...), I hope you can have fun during the contest. Good luck and have fun, wish you high rating!

Full text and comments »

  • Vote: I like it
  • +354
  • Vote: I do not like it

238.
Codeforces Round 1080 (Div. 3)
By chromate00, 7 months ago, In English
Codeforces Round 1080 (Div. 3) Oh hello there. I, [user:chromate00,2026-02-14], am back! Oh no, I hope you are not misunderstanding me, I'm not pulling a joke on the announcement this time. I'm too busy for that right now. So here's the <strike>(mostly copy-pasted)</strike> announcement of [contest:2195]. Anyways. Starting from [contest_time:2195], you will be given **$\mathbf{7}$ or $\mathbf{8}$ problems** to be solved in **$\mathbf{2.5}$ hours**. The round will be hosted by rules of educational rounds (extended ICPC). Thus, all solutions will be judged on preliminary tests during the round, and after the round, there will be a 12-hour phase of **open hacks**. After the open hack phase, all accepted solutions will be rejudged on successful hacks. Also, note that there is no score distribution but the usual penalty of **10 minutes** for each wrong submission, following the rules of educational rounds. [Remind](https://codeforces.me/blog/entry/59228) yourself that only the trusted participants of the third ...
I hope that you will enjoy the contest. Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +266
  • Vote: I do not like it

239.
Codeforces::Gym
By MikeMirzayanov, 15 years ago, translation, In English
Codeforces::Gym <p> We've made it! Or in any case, we are at least very close to it. </p> <p> On January 19, 2012 at 12:00 we open a sub-project called &quot;Gym&quot;. In short, its goal is to enable the Codeforces coders not only to participate in competitions and discuss them, but also to train and coach easily. </p> <p> In fact, despite the wide diversity of online judges in the world, a well thought-out training service system does not exist. So, the expectations from this system are: </p> <ol> <li>Collection of online contests, composed mainly of the past official contests. </li><li> Opportunity to integrate the final standings of past contests in the online contests to be able to train &quot;against&quot; the official participants. </li><li> Opportunity to participate in the training at any time whatsoever, without fear that something breaks down and the server will fall. In short, reliability. </li><li> Opportunity to write virtual contests and to solve the problems in a practice mode. </li...
P.S. A little later I will add some screenshots to the text; it will be fun.

Full text and comments »

  • Vote: I like it
  • +419
  • Vote: I do not like it

240.
Kotlin Heroes 10: Editorial
By BledDest, 2 years ago, In English
Kotlin Heroes 10: Editorial We hope you enjoyed the problems! Thank you for participation. The authors are the usual suspects: [user:Neon,2024-05-15], [user:awoo,2024-05-15], [user:adedalic,2024-05-15], [user:Roms,2024-05-15] and me. Huge thanks to the testers: [user:shnirelman,2024-05-15], [user:KIRIJIJI,2024-05-15], [user:soup,2024-05-15], [user:Optoed,2024-05-15], [user:le.mur,2024-05-15], and the MVP tester [user:PavelKunyavskiy,2024-05-15]. Without your insights, this round would be impossible! [problem:1958A] Idea: [user:BledDest,2024-05-15], preparation: [user:BledDest,2024-05-15] <spoiler summary="Tutorial"> [tutorial:1958A] </spoiler> <spoiler summary="Solution (PavelKunyavskiy)"> ~~~~~ fun main() { val ans = IntArray(101) { Int.MAX_VALUE } ans[0] = 0 for (i in ans.indices) { for ((d, c) in listOf(1 to 1, 3 to 0, 5 to 0)) { if (i + d in ans.indices) ans[i + d] = minOf(ans[i + d], ans[i] + c) } } repeat(readInt()) { prin...
companion object { inline fun from(x: Int) = ModInt((x % MOD + MOD) % MOD) inline, inline operator fun div(other: ModInt) = this * other.inv() inline fun inv() = power(MOD - 2), private fun readInt() = readln().toInt() private fun readLongs() = readStrings().map { it.toLong

Full text and comments »

  • Vote: I like it
  • +32
  • Vote: I do not like it

241.
Educational Codeforces Round 8
By Edvard, history, 11 years ago, translation, In English
Educational Codeforces Round 8 Hello, Codeforces! Educational Codeforces Round 8 will take place on [19 February 2016 at 18:00 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?msg=Educational+Codeforces+Round+8&iso=20160219T1500) for the first and the second divisions. You can read about educational rounds [here](http://codeforces.me/blog/entry/21496) and [here](http://codeforces.me/blog/entry/21565). I hope that the high density of contests on Codeforces will not startle you and you will participate in ER8. \<The phrase about simple problems is added in the end\> The round will be unrated for all users and it will be held with extented ACM ICPC rules. You will have two hours to solve six problems. After that you will have one day to hack any solution you want. You will have access to copy any solution and test it locally. If you have ideas for some problems or maybe already prepared problems that you can't use in rounds or official competitions, you can write to me. It seems that it is har...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +200
  • Vote: I do not like it

242.
OCPC 2024 Fall — wrap
By adamant, history, 2 years ago, In English
OCPC 2024 Fall — wrap Hi everyone! <center><a href="https://ocpc.mathos.unios.hr"><img src="https://ocpc.mathos.unios.hr/images/ocpc.svg" height="100px"></a> <a href="https://icpc.foundation/"><img src="https://ocpc.mathos.unios.hr/images/ICPC.svg" height="100px"></a></center> <center> <b>Sponsored by</b><br> <a href="https://www.janestreet.com/join-jane-street/open-roles/?type=students-and-new-grads&location=london"> <img src="/predownloaded/ee/f2/eef26616a3661c658d1545f18ed21fabb14d5871.svg" height="50px" style="margin: 5px 5px 5px 5px;"> </a> <a href="https://pinely.com/"> <img src="/predownloaded/0a/0f/0a0f3f67435d1f6e467bc7203d4a2090ba8f92cc.svg" height="50px" style="margin: 5px 5px 5px 5px;"> </a> <a href="https://quantco.com/"> <img src="/predownloaded/5d/d5/5dd574cd921167d19fb0907b542835e09e6490f4.svg" height="50px" style="margin: 5px 5px 5px 5px;"> </a> </center> Last Sunday marked the conclusion of the fourth [Osijek Competitive Programming Camp](https://codeforces.me/blog/...
Thank you, QuantCo, for the event! I think it was very fun, and I hope that we can do something

Full text and comments »

  • Vote: I like it
  • +200
  • Vote: I do not like it

243.
Codeforces Round 687 (Div. 1, Div. 2) and Technocup 2021 — Elimination Round 2
By KAN, 6 years ago, translation, In English
Codeforces Round 687 (Div. 1, Div. 2) and Technocup 2021 — Elimination Round 2 Hi all! This weekend, at [contest_time:1415] we will hold Codeforces Round 687. It is based on problems of Technocup 2021 Elimination Round 2 that will be held at the same time. Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at <a href="https://technocup.mail.ru/">Technocup 2021 website</a> and take part in the Elimination Round. Div. 1 and Div.2 editions are open and rated for everyone. Register and enjoy the contests! <p> The problems authors are; [user:amethyst0,2020-11-28], [user:eidan,2020-11-28], [user:Diegogrc,2020-11-28], [user:bensonlzl,2020-11-28], [user:Maripium,2020-11-28], [user:antontrygubO_o,2020-11-28], and [user:KAN,2020-11-28]. Thanks to [user:antontrygubO_o,2020-11-28] and [user:300iq,2020-11-28] for their help in coordination. Also huge thanks to testers for their invaluable help: [user:Golovanov399,2020-11-28], [user:__rkm__,2020-11-28], [user:golions,2020-11-28], [user:dantra...
Have fun!

Full text and comments »

  • Vote: I like it
  • +114
  • Vote: I do not like it

244.
Codeforces Round 692 (Div. 1, Div. 2) and Technocup 2021 — Elimination Round 3
By anta.baka, history, 6 years ago, translation, In English
Codeforces Round 692 (Div. 1, Div. 2) and Technocup 2021 — Elimination Round 3 Hi all! This weekend, at [contest_time:1411] we will hold Codeforces Round 692. It is based on problems of Technocup 2021 Elimination Round 3 that will be held at the same time. Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at <a href="https://technocup.mail.ru/">Technocup 2021 website</a> and take part in the Elimination Round. Div. 1 and Div.2 editions are open and rated for everyone. Register and enjoy the contests! The Elimination Round authors are [user:neckbotov,2020-12-19] and [user:sincerity,2020-12-19]. Thanks to [user:Nebuchadnezzar,2020-12-19] and [user:KAN,2020-12-19] for their coordination. Also huge thanks to testers for their invaluable help: [user:isaf27,2020-12-19], [user:300iq,2020-12-19], [user:Kaban-5,2020-12-19], [user:low_,2020-12-19], [user:Himanshu_77,2020-12-19], [user:wiwitrifai,2020-12-19], [user:Ashishgup,2020-12-19], [user:spar5h,2020-12-19], [user:Nemo,2020-12-19], [u...
Have fun!

Full text and comments »

  • Vote: I like it
  • +295
  • Vote: I do not like it

245.
[Contest] Statement Not Found: Season 2
By zscoder, history, 4 years ago, In English
[Contest] Statement Not Found: Season 2 #### Do you think you can solve CP problems without reading the problem statements? Let's find out! On [August 28, 2022 (Sunday) 19:30-22:00 GMT+8](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Statement+Not+Found+-+Season+2&iso=20220828T1930&p1=122&ah=2&am=30), I will hold an unofficial fun contest called Statement Not Found. As you can deduce from the title, there will be no problem statements (except title and samples). Your goal is to collect as many points as possible within 2.5 hours :) Obviously, this round is **unrated**. It is somewhere between April Fools contest and a legitimate contest. The contest will be OI-style, meaning there will be no time penalty. You are allowed to use any resources online to help solve the problems. There will be **12** problems. **Scoring Distribution:** 200-400-700-700-700-800-800-900-1100-1100-1100-1500 (Total: 10000) **Please read all problems** as problem difficulty is very subjective and a 1100-point problem might b...
hours**. Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +308
  • Vote: I do not like it

246.
Codeforces Round 1025 (Div. 2) Editorial
By FetFot, 16 months ago, In English
Codeforces Round 1025 (Div. 2) Editorial Thank you for your participation! We hope you enjoyed the problems! We would love to hear your feedback! Please share your thoughts in the comments. <br> <spoiler summary="How did you find the contest?"> - Great: - Good: - Average: - Bad: - Trash: </spoiler> <spoiler summary="Which problem was your favorite?"> - A: - B: - C1: - C2: - C3: - D: - E: - F: </spoiler> <spoiler summary="Which problem did you find the least enjoyable?"> - A: - B: - C1: - C2: - C3: - D: - E: - F: </spoiler> <br> [problem:2109A] Idea by [user:MOUFLESS,2025-05-17], prepared by [user:MO...

Full text and comments »

  • Vote: I like it
  • +251
  • Vote: I do not like it

247.
AI might erase CP, but not us
By purplesyringa, history, 23 months ago, In English
AI might erase CP, but not us I haven't slept for 20 hours and I can't fall asleep. I've been reading others' topics on AI, and I had a sort of epiphany. These ideas have been brewing inside me for many years, and I thought it might be time to share them with the community. --- There were times when I was a "competitive programmer" at the core. I spent many years doing that exclusively. I've never been to IOI, but I like to think that I've reached some good heights. Two years ago, I stopped writing online competitions. I've written a few offline competitions after that, but eventually, I decided to stop that too. Yet somehow Codeforces still attracts me. I don't want to solve problems, but I keep typing codeforces.com into the address bar. *Why?* Just yesterday, I didn't have an answer. --- Imagine a layperson asking you what competitive programming is. What are you going to say? My answer has always been "Oh, we solve interesting algorithmic problems with time constraints and other limits". Many ...
it's fun., But *why* is it fun to me specifically? I'm in the minority here, but I hate writing rounds. I know

Full text and comments »

  • Vote: I like it
  • +293
  • Vote: I do not like it

248.
ICPC 2023 Online Challenge powered by Huawei
By ICPCNews, 3 years ago, In English
ICPC 2023 Online Challenge powered by Huawei <img src="/predownloaded/60/ed/60eddb18a54159e57dd1ffc836857f58420039bf.jpg" align="right" style="height: 280px;" alt="text"/> #### Hello, Codeforces! From the ICPC 2023 World Finals, we are happy to bring you an exciting online event: **The ICPC 2023 Online Challenge powered by Huawei**，which will start on November 20, 2023 15:00 UTC (UTC+8) In this Challenge, you will have a unique chance: - to **compete with top programmers globally** - to **solve 1 exciting problem** prepared by Huawei - to **win amazing prizes** from Huawei! **It is an individual competition.** #### The ICPC 2023 Online Challenge powered by Huawei: **Start:** [November 20, 2023 15:00 (UTC+8)](https://www.timeanddate.com/worldclock/fixedtime.html?day=20&month=11&year=2023&hour=10&min=0&sec=0&p1=166) **Finish:** [December 4, 2023 15:00 (UTC+8)](https://www.timeanddate.com/worldclock/fixedtime.html?day=04&month=12&year=2023&hour=10&min=0&sec=0&p1=166) **We hope you'll enjoy this ...
**Good luck, we hope this will be fun!**

Full text and comments »

  • Vote: I like it
  • +387
  • Vote: I do not like it

249.
Educational Codeforces Round 182 [Rated for Div. 2]
By awoo, history, 12 months ago, translation, In English
Educational Codeforces Round 182 [Rated for Div. 2] <img alt="Neapolis University Pafos" src="/predownloaded/9a/33/9a332fadbb47050ba9405057df022a6e37eaf5c0.png" style="float:right;height: 200px; margin: 10px; max-width:40%;"/> Hello Codeforces! The series of Educational Rounds continues thanks to the support of the [Neapolis University Pafos](https://www.nup.ac.cy/). They offer a BSc in Computer Science and AI with [JetBrains Scholarships] (https://lp.jetbrains.com/academy/csai-program/). Gain cutting-edge skills in AI and machine learning, preparing you for high-demand tech careers. Limited scholarships available &mdash; don't miss your chance to study in Europe for free! On [contest_time:2144] [contest:2144] will start. This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You w...
_Don't miss the chance to sharpen your skills (and enjoy some fun mashup contests, curated by

Full text and comments »

  • Vote: I like it
  • +128
  • Vote: I do not like it

250.
random quotes
By Lyde, history, 3 years ago, In English
random quotes Oh hi! Welcome to 24 random quotes! I'm a competitive programmer, but I'm also pretty much a fan and often visit here to see some recent actions. I have a pretty unusual hobby: Collecting some sentences from blogs and comments and saving them as pictures, which I could use later for memes. Later I realized that I couldn't use it that much and after 4 years, it became a collection of well, memories. So I had the idea of sharing some of it with you guys for nostalgia! Most of them are light-hearted, and all of them are pretty memorable in my mind. If you are an experienced member here you might realize some of them, so I will make it a challenge: Guess where this is from! (No prizes sadly) The spoiler to the link of the comment/blog and my personal opinion (or s/p) will be right below the quote. Anyways, enjoy. > If newcomers find it confusing, then that's their bugaboo <spoiler summary="s/p"> [Link](https://codeforces.me/blog/entry/91480#comment-800196) Still rem...
> Dude, I'm not having fun solving problems, I'm having fun learning useless algorithms. Get lost.

Full text and comments »

  • Vote: I like it
  • +198
  • Vote: I do not like it

251.
Codeforces: Results of 2013
By MikeMirzayanov, 13 years ago, translation, In English
Codeforces: Results of 2013 Hello! Do you feel the breath of New Year? <img src="http://assets.codeforces.com/images/tree.png" style="float:right;margin: 0 1em 1em 1em;"/> The clock shows a day before New Year, so it is time to sum up the past. I do not have speech-writers for words in the style of "what recently seemed almost impossible, it becomes a fact of life" so I'll be short. Thank you all! Your unfading interest and constant help inspire Codeforces team for new achievements! Brilliant writers, invisible soldiers: testers, tireless and greedy for knowledge participants &mdash; all of you help Codeforces do better! I've dug into the records and made a partial list of the most notable major improvements of 2013. Some large improvements of our infrastructure are not in the list, as the community can not see them directly. * A simple way to add contest from [Polygon](https://polygon.codeforces.com/) to Codeforces::Gym. * Drafts embedded in text form fields in Codeforces and Polygon. * Multipl...
fun pictures. Here is a series of images showing the growth of Codeforces:

Full text and comments »

  • Vote: I like it
  • +601
  • Vote: I do not like it

252.
Technocup 2022 — Elimination Round 2 and Codeforces Round #755 (Div. 1, Div. 2)
By isaf27, history, 5 years ago, translation, In English
Technocup 2022 — Elimination Round 2 and Codeforces Round #755 (Div. 1, Div. 2) Hi all! This weekend, at [contest_time:1584] we will hold [contest:1588] and [contest:1589]. They are based on problems of Technocup 2022 Elimination Round 2 that will be held at the same time. Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at <a href="https://technocup.mail.ru/">Technocup website</a> and take part in the Elimination Round. Div. 1 and Div.2 editions are open and rated for everyone. Register and enjoy the contests! - The round authors are: [user:Denisson,2021-11-13], [user:antonis.white,2021-11-13], [user:dimatimoshin23,2021-11-13], [user:__JustMe__,2021-11-13], [user:4qqqq,2021-11-13], [user:Aleks5d,2021-11-13] - Coordinator: [user:isaf27,2021-11-13] - Thanks [user:KAN,2021-11-13] for help with round preparation, also thanks [user:MikeMirzayanov,2021-11-13] for the great Codeforces and Polygon systems. - Thanks [user:221,2021-11-13], [user:Makcum888,2021-11-13], [user:Melonad...
Have fun!

Full text and comments »

  • Vote: I like it
  • +173
  • Vote: I do not like it

253.
Invitation to TOKI Regular Open Contest #24
By errorgorn, 5 years ago, In English
Invitation to TOKI Regular Open Contest #24 Hello again Codeforces &#x1f44b;, We are excited to invite you to **TOKI Regular Open Contest #24**! Key details: - Contest link: [TLX](https://tlx.toki.id/contests/troc-24) - Time: [18th December 2021, 13:05 UTC](https://www.timeanddate.com/worldclock/fixedtime.html?msg=TOKI+Regular+Open+Contest+%2324&iso=20211218T1305&p1=1440&ah=2&am=30) - Writers: [user:errorgorn,2021-12-13], [user:maomao90,2021-12-13], [user:oolimry,2021-12-13] - Duration: 150 minutes - Problems: 7, but one of the problems will have a subtask - Scoring distribution: **100 &mdash; 200 &mdash; 400 &mdash; 600 &mdash; (600 + 200) &mdash; 900 &mdash; 1000** Many thanks to: - [user:prabowo,2021-12-13] &#x1f468;&zwj;&#x2764;&#xfe0f;&zwj;&#x1f48b;&zwj;&#x1f468; for &#x1f552; coordinating the &#x1f466;&#x1f337; contest and translating our &#x1f4b0;&#x1f171; stupid &#x1f615;&#x1f4a9; jokes into &#x27a1; Indonesian &#x1f1ee;&#x1f1e9;. - [user:icypiggy,2021-12-13] for helping &#x1f4bb; us &#x1f1...
😘 enjoy 😋💋 the contest! Good 👌 luck 😄 have 😏😝 fun!

Full text and comments »

  • Vote: I like it
  • +227
  • Vote: I do not like it

254.
Codeforces Round 987 (Div. 2) Editorial
By ACGN, history, 22 months ago, In English
Codeforces Round 987 (Div. 2) Editorial <spoiler summary="A little backstory about the round (ACGN)">The Highschool CPers (HSCP) Discord server was created in April 2022 by [user:pwned,2024-11-14], which over time grew into a close-knit community of highschool competitive programmers. I joined in the same month of its creation, and in the next month I approached [user:pwned,2024-11-14] about the possibility of setting a contest. Thus the HSCP round concept was born. Over the next month or so, the initial problems were born; the current problems A and F were produced in June-July 2022. We had several problem ideas by then, enough to set a div.2 round. However, as I was going to be busy in my 5th year of high school, and may not be that responsive to coordinators, the contest was in the ownership of [user:pwned,2024-11-14], who needed to wait until he reached master in order to propose the set on Codeforces. However, this step took almost 1.5 years as he would stay at candidate master for 57 consecutive contests, eve...
That's it for this round, and we hope you had fun with all the problems!

Full text and comments »

  • Vote: I like it
  • +282
  • Vote: I do not like it

255.
After-stream thoughts
By Errichto, 8 years ago, In English
After-stream thoughts Hello again. Next stream will start tomorrow (Wednesday) at 2pm CEST ([your timezone](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Errichto+Stream+%233&iso=20181003T14&p1=262)), solving problems from POI 22, round 1 ([link](https://szkopul.edu.pl/p/default/problemset_eng/oi/22)). It will be on my [Youtube channel](https://www.youtube.com/channel/UCBr_Fu6q9iHYQCh13jmpbrg). I did two streams this weekend that you can now find on my youtube [channel](https://www.youtube.com/channel/UCBr_Fu6q9iHYQCh13jmpbrg). The first with quite easy Codeforces problems that I solved from scratch (I haven't seen them before), also implementing them. The second one with a bit harder Topcoder problems that I've solved before, but I didn't necessarily remember the solution now &mdash; and for those I only described the solution, without implementation. The streams were fine but there are a lot of things to improve. I wanted to see two things: 1. Can I stream? Am I able to try to sol...
useful for anybody here, but it would be a bit of fun and any programmer could watch that.

Full text and comments »

  • Vote: I like it
  • +240
  • Vote: I do not like it

256.
Codeforces Round 917 (Div. 2)
By _LeMur_, 3 years ago, In English
Codeforces Round 917 (Div. 2) Hi, Codeforces! I'm glad to invite you to take part in [Codeforces Round 917](https://codeforces.me/contests/1917), which will take place on [contest_time:1917]. **Round will be rated for participants with rating less than $2100$.** Participants from the first division can take part out of competition. There will be $6$ problems for $2$ hours. The problems are authored by [user:igori,2023-12-24], [user:zidder,2023-12-24] and me. **Part of the problems in this round were in the Yerevan SU 28.1₀.₂₀₂3 Contest. If you participated in it or know at least one problem from it, please refrain from participating in this round.** We would like to thank - Thanks to [user:thescrasse,2023-12-22] for excellent round coordination; - Thanks to our testers: [user:KAN,2023-12-22], [user:S_Voloch,2023-12-22], [user:Tmitmi,2023-12-22], [user:Pagode_Paiva,2023-12-22], [user:hgglmao,2023-12-22], [user:IceWolf898,2023-12-22], [user:daud04,2023-12-22], [user:dewana310,2023-12-22], [user:menbo...
We hope you'll like the problemset! Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +281
  • Vote: I do not like it

257.
Online mirror of The 2024 ICPC Asia Jakarta Regional Contest
By Pyqe, 21 month(s) ago, In English
Online mirror of The 2024 ICPC Asia Jakarta Regional Contest Selamat pagi Codeforces! We're going to hold The 2024 ICPC Asia Jakarta Regional Contest. We invite you to join the online mirror contest [2024-2025 ICPC, Asia Jakarta Regional Contest (Online Mirror, Unrated, ICPC Rules, Teams Preferred)](https://codeforces.me/contests/2045) on Codeforces. It'll be held on [contest_time:2045] and will last for 5 hours. The mirror will be held using ICPC-style scoring with 10 to 13 problems. The problem statements will only be available in English. We encourage participating as a team using only one computer for coding (as in ICPC contests). The mirror will be unrated. Some useful links: * [The 2024 ICPC Asia Jakarta homepage](https://competition.binus.ac.id/icpc2024) * [The regional information in ICPC Global](https://icpc.global/regionals/finder/Jakarta) * [The onsite scoreboard](https://competition.binus.ac.id/contest) We hope that you'll enjoy the contest. Good luck and have fun! **UPD.** The mirror has ended! You can find...
We hope that you'll enjoy the contest. Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +174
  • Vote: I do not like it

258.
2024 ICPC Asia Taichung Regional Contest [Online Mirror, ICPC Rules]
By tmt514, history, 21 month(s) ago, In English
2024 ICPC Asia Taichung Regional Contest [Online Mirror, ICPC Rules] Hello Codeforces! I am pleased to invite you to participate in [contest:2041], which will be held on [contest_time:2041]. This is an online mirror contest for the 2024 ICPC Asia Taichung Regional Contest, and the official offline contest was conducted on November 17th, 2024. The duration of the contest will be 5 hours and the contest is best for **teams of three people**. The mirror will use the ICPC format. The contest tasks are proposed by the task authors ([user:baluteshih,2024-11-21], [user:waynetuinfor,2024-11-21], [user:skylinebaby,2024-11-21],[user:samsam2310,2024-11-21], [user:hank55663,2024-11-21], [user:ltf0501,2024-11-21], [user:Jeffrey,2024-11-21], [user:shik,2024-11-21], [user:tmt514,2024-11-21], Bangye Wu, [user:kasuistry,2024-11-21], and Peter Rossmanith), prepared and polished by the judge team (Regional Contest Director Ling-Ju Hung, Chief Judge Peter Rossmanith, [user:kasuistry,2024-11-21], Hung-Lung Wang, [user:baluteshih,2024-11-21], [user:waynetuinfor,2024...
contest and have fun!

Full text and comments »

  • Vote: I like it
  • +290
  • Vote: I do not like it

259.
Noon Cake Programming Contest 2026 Announcement
By TripleM5da, history, 10 months ago, In English
Noon Cake Programming Contest 2026 Announcement Hello Codeforces! Noon is thrilled to invite you to participate in the first-ever Noon Cake Programming Contest (NCPC)! Noon is building the future of e-commerce for the Middle East, and we are powered by a world-class engineering team. We're passionate about problem-solving and competitive programming, and we want to celebrate that with the community. ![ ](/predownloaded/da/c6/dac6a72f133817c7fc0d42b7d5da74d9af24761f.png) Our problem-setting team includes several ICPC World Finalists and IOI Medalists who have crafted an exciting set of challenges for you. We can't wait for you to try them! The contest will be held in two phases: Phase 1: Qualification Round This round is open to everyone, all around the world! It's your chance to test your skills against a high-quality problem set and have fun. <br> Date: 2026-01-31 <br> Time: 12:35 EGY (UTC+2) <br> Duration: 4 hours <br> Who: Everyone! <br> Registration: [form](https://docs.google.com/forms/d/e/1FAIpQLS...
. Good luck, and have fun! — The Noon Team

Full text and comments »

  • Vote: I like it
  • +271
  • Vote: I do not like it

260.
Let's solve some hard problems!
By ivan100sic, history, 5 years ago, In English
Let's solve some hard problems! Tonight, I will pick twelve 3000 rated problems I haven't solved yet, try solving them, and track my progress. As usual, I will not look at editorials. Hopefully I will be able to solve them all before the year ends. I will not make this my highest priority and I won't try too hard. I will keep solving other problems in the meantime. The problems are: 1. [problem:341E] (solved Jan 14, 12 days) 2. [problem:843E] 3. [problem:1250D] (solved Jan 5, 3 days) 4. [problem:573D] (solved Jan 6, 4 days) 5. [problem:1290D] (solved Jan 8, 6 days) 6. [problem:568E] 7. [problem:788D] (solved Jan 14, 12 days) 8. [problem:698F] (solved Jan 3, 1 day) 9. [problem:1342F] (solved Jan 4, 2 days) 10. [problem:1236F] (solved Jan 3, 1 day) 11. [problem:533A] (solved Jan 16, 14 days) 12. [problem:1411F] (solved Jan 22, 20 days) My thoughts on the problems I have solved: <spoiler summary="Problem 1"> I had a lot of fun solving this! <spoiler summary="My solution"> I use only a few tho...
I had a lot of fun solving this!

Full text and comments »

  • Vote: I like it
  • +197
  • Vote: I do not like it

261.
A story about the worst contest organization ever. Or how to invent rules to have rules.
By peltorator, 2 years ago, In English
A story about the worst contest organization ever. Or how to invent rules to have rules. Today, the European Championship was held in Prague. The first of its kind. And it was... the worst organized contest I have ever participated in. This is not only sad in isolation but also especially sad as the contest itself (the problems) was actually nice, and I would like to thank the authors for that! So what was so bad about it? Let me describe how entering the contest works. One first goes to the cloakroom. Then, one proceeds via a long corridor to another building, where in a relatively small space, all teams gather for half an hour. Then, "id check" begins. I mean... I have never seen this before but in itself, there is nothing wrong with it. They want to check your identity. Makes sense. However, what do you think would be a reasonable way to do it? I would think that one and only reasonable way to do it is the following: one comes to the entrance of the contest area, a volunteer checks their id and matches with their badge, and the contestant comes in. As you could ha...
. But this one... This one was pure fun. As a final rule that comes out of nowhere: [link](https

Full text and comments »

  • Vote: I like it
  • +316
  • Vote: I do not like it

262.
Codeforces Round #369 (Div. 2)
By zscoder, history, 10 years ago, In English
Codeforces Round #369 (Div. 2) **Important Update:** Our friends have noticed that the upcoming round collides with their contest and also weekend is full of many another contests, so the round is now **moved** to **Monday**, [29 August 2016 15:05 MSK](http://timeanddate.com/worldclock/fixedtime.html?day=29&month=8&year=2016&hour=15&min=5&sec=0&p1=166). We are sorry for the inconvenience caused and hope that you'll understand us. Hi everyone! Codeforces Round #369 (Div. 2) will take place on [27 August 2016 at 16:05 MSK](http://timeanddate.com/worldclock/fixedtime.html?day=27&month=8&year=2016&hour=16&min=5&sec=0&p1=166). As usual, Div.1 participants can join out of competition. I would like to thank [user:dans,2016-08-26] for helping me with the preparation of the round, [user:MikeMirzayanov,2016-08-26] for the amazing Codeforces and Polygon platforms and also [user:Phyto,2016-08-26] for testing the problems. I am the author of all the problems, and [user:dans,2016-08-26] also helped making one of the...
Good luck, have fun, and wish everyone many **Accepted Solutions**. :)

Full text and comments »

  • Vote: I like it
  • +286
  • Vote: I do not like it

263.
Kotlin Heroes 8 Editorial
By BledDest, 5 years ago, In English
Kotlin Heroes 8 Editorial First of all, I would like to thank all testers of the round: [user:pashka,2021-10-08], [user:FlakeLCR,2021-10-08], [user:peti1234,2021-10-08], [user:Akulyat,2021-10-08], [user:bugdone,2021-10-08], [user:pacha2880,2021-10-08]. Also huge thanks to co-authors of the contest: [user:Neon,2021-10-08], [user:adedalic,2021-10-08] and [user:awoo,2021-10-08]. I hope you enjoyed participating in the round! Okay, now for the editorial itself: [problem:1571A] Idea: [user:BledDest,2021-10-08], preparation: [user:Neon,2021-10-08] <spoiler summary="Tutorial"> [tutorial:1571A] </spoiler> <spoiler summary="Solution (Neon)"> ~~~~~ fun main() = repeat(readLine()!!.toInt()) { val s = readLine()!! val l = s.count({ it == '<' }) val g = s.count({ it == '>' }) if (l > 0 && g > 0) println("?") else if (l > 0) println("<"); else if (g > 0) println(">"); else println("="); } ~~~~~ </spoiler> [problem:1571B] Idea: [user:BledDest,2021-10-08], preparation: ...
private fun readInt() = read().toInt() private fun readLong() = read().toLong() privatefun

Full text and comments »

  • Vote: I like it
  • +60
  • Vote: I do not like it

264.
Codeforces Round 1007 (Div. 2)
By FetFot, 18 months ago, In English
Codeforces Round 1007 (Div. 2) <h1>مرحبا, Codeforces!</h1> Translation: Hello, Codeforces! We are super excited to invite you to participate in [Codeforces Round 1007 (Div. 2)](https://codeforces.me/contest/2071), which will be held on [Friday, February 28, 2025 at 17:35](https://www.timeanddate.com/worldclock/fixedtime.html?day=28&month=2&year=2025&hour=17&min=35&sec=0&p1=166). This round will be **rated for all participants with rating below $2100$**. Participants with higher ratings are encouraged to participate out of the competition. You will be presented with **$6$ or $7$ problems** and **$2$ hours and $15$ minutes** to solve them. The problems are authored and prepared by [user:Al-Merreikh,2025-02-25], [user:ApraCadabra,2025-02-25], [user:FzArK,2025-02-25], [user:limbo16,2025-02-25], [user:MOUFLESS,2025-02-25], and [user:Vectors_Master,2025-02-25]. We would like to thank everyone who made this round possible: - [user:Sugar_fan,2025-02-25] for coordinating the round and helping with problem pr...
We hope you will find a non-empty subset of problems to be interesting. Good luck, havefun and see

Full text and comments »

  • Vote: I like it
  • +343
  • Vote: I do not like it

265.
Kotlin Heroes Editorial
By vovuh, history, 7 years ago, In English
Kotlin Heroes Editorial [problem:1170A] Idea: [user:Vovuh,2019-05-28] Solution: [user:elizarov,2019-05-28] <spoiler summary="Tutorial"> [tutorial:1170A] </spoiler> <spoiler summary="Solution"> ~~~~~ fun main() { val q = readLine()!!.toInt() repeat(q) { val (x, y) = readLine()!!.split(" ").map { it.toInt() }.sorted() println("1 ${x - 1} ${y - x + 1}") } } ~~~~~ </spoiler> [problem:1170B] Idea: [user:MikeMirzayanov,2019-05-28] Solution: [user:elizarov,2019-05-28] <spoiler summary="Tutorial"> [tutorial:1170B] </spoiler> <spoiler summary="Solution"> ~~~~~ fun main() { val n = readLine()!!.toInt() val a = readLine()!!.split(" ").map { it.toInt() } var m1 = 0 var m2 = 0 var c = 0 for (x in a) { if (m2 > x) { c++ } when { x > m1 -> { m2 = m1 m1 = x } x > m2 -> { m2 = x ...
fun next() = readLine()!! fun nextInt() = next().toInt() fun nextInts() = next().split(" ").map, private fun readInt() = readLine()!!.toInt() private fun readInts() = readLine()!!.split(" ").map

Full text and comments »

  • Vote: I like it
  • +47
  • Vote: I do not like it

266.
Codeforces Round 1030 (Div. 2)
By szilb, 15 months ago, In English
Codeforces Round 1030 (Div. 2) Üdv, Codeforces! [user:Error-42,2025-06-10], [user:gortomi,2025-06-10] and I are glad to invite everyone to participate in [contest:2118], which will be held on [contest_time:2118]. You will be given 6 problems and 1 subtask with 2 hours to solve them. The round will be rated for participants of Division 2 with a rating lower than 2100. Division 1 participants can participate unofficially. All problems are authored by [user:Error-42,2025-06-10], [user:gortomi,2025-06-10] and me. We would like to thank: - [user:satyam343,2025-06-10] for their amazing coordination and for rejecting our bad ideas ${\color{white}{\text{and several other problems too.}}}$ - [user:peti1234,2025-06-10] for their LGM opinion. - [user:Alexdat2000,2025-06-10] for the Russian translations. - [user:N_z__,2025-06-10], [user:Error_Yuan,2025-06-10], [user:_istil,2025-06-10], [user:busamate,2025-06-10], [user:andrei_boaca,2025-06-10], [user:Dominater069,2025-06-10], [user:nifeshe,2025-06-10] fo...
We hope you will enjoy and have fun in the contest. Sok szerencsét!

Full text and comments »

  • Vote: I like it
  • +311
  • Vote: I do not like it

267.
Invitation to CodeChef SnackDown Elimination and Parallel Rated Contests
By antontrygubO_o, 5 years ago, In English
Invitation to CodeChef SnackDown Elimination and Parallel Rated Contests We are very glad to invite you to participate in [SnackDown Elimination round](https://www.codechef.com/SNCKEL21)! It will be **rated** for all participants. 60 participants will qualify for the finals from the Elimination round. They include: <ul> <li>The top 25 participants from the Elimination round.</li> <br> <li>Additional top 2 school participants </li> <br> <li>Additional top 2 female participants </li> <br> <li>Additional 31 Indian participants, including: <ul> <li> 10 top Indian participants </li> <br> <li> The next 15 Indian participants from the Elimination Round qualify provided they solve at least 2 problems. </li> <br> <li> 3 top Indian School participants</li> <br> <li> 3 top Indian Female participants </li> </ul> </li> </ul> Those, who haven't advanced, are invited to participate in the [Parallel rounds](https://www.codechef.com/SDELP21), which will be held for all divisions. All three rounds are **rated** too. [Time: 7:30 PM ...
Hope to see you participating. Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +123
  • Vote: I do not like it

268.
Educational Codeforces Round 7
By Edvard, history, 11 years ago, translation, In English
Educational Codeforces Round 7 Hello, Codeforces! Educational Codeforces Round 7 will take place on [10 February 2016 at 18:00 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?msg=Educational+Codeforces+Round+7&iso=20160210T1500) for the first and second divisions. You can read about educational rounds [here](http://codeforces.me/blog/entry/21496) and [here](http://codeforces.me/blog/entry/21565). \<This paragraph was modified last time\> The round will be unrated for all users and it will be held with extented ACM ICPC rules. You will have two hours to solve six problems. After that you will have one day to hack any solution you want. You will have access to copy any solution and test it locally. If you have ideas for some problems or maybe already prepared problems that you can't use in rounds or official competitions, you can write to me. \</This paragraph was modified last time\> Thanks a lot to Aleksa Plavsic [user:allllekssssa,2016-02-08] who suggested the problems D, E and Ivan Po...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +313
  • Vote: I do not like it

269.
Educational Codeforces Round 126 Editorial
By awoo, history, 4 years ago, translation, In English
Educational Codeforces Round 126 Editorial [problem:1661A] Idea: [user:BledDest,2022-04-10] <spoiler summary="Tutorial"> [tutorial:1661A] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ import kotlin.math.abs fun sum(a1: Int, a2: Int, b1: Int, b2: Int) = abs(a1 - a2) + abs(b1 - b2) fun main() { repeat(readLine()!!.toInt()) { val n = readLine()!!.toInt() val a = readLine()!!.split(' ').map { it.toInt() }.toIntArray() val b = readLine()!!.split(' ').map { it.toInt() }.toIntArray() var sum = 0L for (i in 1 until n) { if (sum(a[i - 1], a[i], b[i - 1], b[i]) > sum(a[i - 1], b[i], b[i - 1], a[i])) a[i] = b[i].also { b[i] = a[i] } sum += sum(a[i - 1], a[i], b[i - 1], b[i]) } println(sum) } } ~~~~~ </spoiler> [problem:1661B] Idea: [user:adedalic,2022-04-10] <spoiler summary="Tutorial"> [tutorial:1661B] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ fun main(...
fun sum(a1: Int, a2: Int, b1: Int, b2: Int) = abs(a1 - a2) + abs(b1 - b2), ~~~~~ fun main() { val n = readLine()!!.toInt() val a = readLine()!!.split(' ').map

Full text and comments »

  • Vote: I like it
  • +88
  • Vote: I do not like it

270.
Codeforces Round 929 (Div. 3)
By erniepsycholone, 3 years ago, In English
Codeforces Round 929 (Div. 3) _“It is not important to be better than someone else, but to be better than you were yesterday.”_ — Master Oogway, Kung Fu Panda Hello, Codeforces! We are proud to present [contest:1933], and we hereby invite all of you to take part in it. This round will start on [contest_time:1933]. You will have **2 hours and 15 minutes** to solve **7 problems**. The **penalty** for a wrong submission is equal to **10 minutes**. This round will be rated for participants with ratings lower than 1600. However, all of you who wish to take part and have a rating of 1600 or higher, are welcome to register for the round unofficially. The round will be hosted by rules of educational rounds (extended ICPC). Thus, solutions will be judged on preliminary tests during the round, and after the round, it will be a 12-hour phase of open hacks. Remember that only the trusted participants of the third division will be included in the official standings table. As stated in [this blog](https://codeforce...
exposure to competitive programming and make you _better than you were yesterday_. Havefun!

Full text and comments »

  • Vote: I like it
  • +444
  • Vote: I do not like it

271.
Codeforces Round #769 (Div. 2)
By Igorfardoc, history, 5 years ago, In English
Codeforces Round #769 (Div. 2) #### Hi, Codeforces! [user:Vladithur,2022-01-28] and I are pleased to invite you to our [contest:1632], which will be held on [contest_time:1632]. **This round will be rated for participants with rating lower than 2100.** We would like to express our great gratitude to: - [user:irkstepanov,2022-01-28] and [user:KAN,2022-01-28] for <strike>not rejecting our tasks</strike> excellent coordination of the round and assistance in preparing problems. - [user:Ormlis,2022-01-28], [user:antontrygubO_o,2022-01-28], [user:generic_placeholder_name,2022-01-28], [user:Alexdat2000,2022-01-28], [user:Dart-Xeyter,2022-01-28], [user:wxhtzdy,2022-01-28], [user:sohsoh,2022-01-28], [user:zer0brain,2022-01-28], [user:radal,2022-01-28], [user:dbsic211,2022-01-28], [user:stevancv,2022-01-28], [user:maxverr,2022-01-28], [user:Scrubpai,2022-01-28], [user:Artem1303,2022-01-28], [user:RomkaRomantic,2022-01-28] and [user:MaxShch,2022-01-28] for testing the round and providing useful feedback. - [user:MikeM...
hope you will have fun and increase your rating!

Full text and comments »

  • Vote: I like it
  • +394
  • Vote: I do not like it

272.
Codeforces Round #225
By fchirica, 13 years ago, In English
Codeforces Round #225 Hello everyone! We invite you to participate at Codeforces Round #225, scheduled [Monday, 20th January at 7:30 PM MSK](http://www.timeanddate.com/worldclock/fixedtime.html?day=20&month=1&year=2014&hour=19&min=30&sec=0&p1=166). This is the third round I coauthor, along with [contest:341] (and of course Div. 2 version of contest) and [contest:327]. If you recall my old rounds, you'll see that main character is Iahub. The other writer of this round is... Iahub... the real person corresponding to "Iahub" character. Let me introduce you to Rares Buhai ([user:rares.buhai,2014-01-18]). He's the author of Div. 2 C / Div. 1 A, Div. 1 D and Div. 1 E. You can expect those problems to be interesting, coming from a [2 times IOI gold medalist](http://ioi.eduardische.com/people/2688) (being allowed to participate 2 more times). All other problems are created by me. I like them, but I wouldn't be objective if I said that they're interesting. Let's see if someone will think so after the contest ...
We wish everyone high rating and to have fun!

Full text and comments »

  • Vote: I like it
  • +353
  • Vote: I do not like it

273.
Educational Codeforces Round 146 Editorial
By awoo, history, 3 years ago, translation, In English
Educational Codeforces Round 146 Editorial [problem:1814A] Idea: [user:BledDest,2023-04-07] <spoiler summary="Tutorial"> [tutorial:1814A] </spoiler> <spoiler summary="Solution (awoo)"> ~~~~~ for _ in range(int(input())): n, k = map(int, input().split()) for x in range(2): if n - x * k >= 0 and (n - x * k) % 2 == 0: print("YES") break else: print("NO") ~~~~~ </spoiler> [problem:1814B] Idea: [user:BledDest,2023-04-07] <spoiler summary="Tutorial"> [tutorial:1814B] </spoiler> <spoiler summary="Solution (awoo)"> ~~~~~ for _ in range(int(input())): a, b = map(int, input().split()) ans = a + b for m in range(1, 100000): ans = min(ans, (a + m - 1) // m + (b + m - 1) // m + (m - 1)) print(ans) ~~~~~ </spoiler> [problem:1814C] Idea: [user:BledDest,2023-04-07] <spoiler summary="Tutorial"> [tutorial:1814C] </spoiler> <spoiler summary="Solution (BledDest)"> ~~~~~ #include<bits/stdc++.h> using namespace std; int main() { int t; scanf("%d", &t...
fun checkAround(pos : Long) : Int { val qs = Array(2 * k + 1) { MutableList(0) { 0 } }

Full text and comments »

  • Vote: I like it
  • +68
  • Vote: I do not like it

274.
Codeforces Round #502 (in memory of Leopoldo Taravilse, Div. 1 + Div. 2)
By Magolor, history, 8 years ago, In English
Codeforces Round #502 (in memory of Leopoldo Taravilse, Div. 1 + Div. 2) > This round is in memory of Leopoldo Taravilse. > > Leopoldo Taravilse (ltaravilse) was a distinguished member of the competitive programming community in Argentina and Latin America. As a contestant, he reached the ACM-ICPC World Finals in 2010 and 2012, and was active in CodeForces and TopCoder. After 2012 he became a problemsetter for the ACM-ICPC South American regionals and the Argentinian Programming Tournament, and later coach for a World Finalist team in 2016. > > Leopoldo's passion was helping others realize their full potential in competitive programming. He taught at various competitive programming schools in Brazil, Cuba, Peru and Bolivia, and his role organizing the Argentinian Training Camp cannot be overstated. Under his wing, it grew from a small group of friends in 2010 to a major event featuring international sponsors and having hundreds of participants coming from all corners of Latin America. Through successive editions of the Training Camp, Leopoldo inspired s...
students to learn and improve, to give back to the community, and to have fun doing it. > > With

Full text and comments »

  • Vote: I like it
  • +812
  • Vote: I do not like it

275.
Order Capital Round 2 (Codeforces Round 1104, Div. 1 + Div. 2)
By _ja, 3 months ago, In English
Order Capital Round 2 (Codeforces Round 1104, Div. 1 + Div. 2) Hello / Selamat sejahtera / 你好 Codeforces! ================== <div style="float:right; margin-left:15px; width:200px;"> <img src="/predownloaded/80/7f/807f4117591c25d5cd189f81cecec2afc0afceef.jpg" width="200px" > <div style="font-size:smaller; text-align:center;"> Crochet penguin plushie,<br> credits to [user:gry3125,2026-06-15] </div> </div> We, [user:quacksaysduck,2026-06-15] and [user:_ja,2026-06-15] are excited to invite you to [contest:2237], which will start on [contest_time:2237]! In this round, you will help Ja the Ghost and Quack the Duck on their daily shenanigans. <strike>This round will be in the format of an IMO mock.</strike> There will be $9$ problems which you will have to solve in $3$ hours. This round will be combined for Division 1 and Division 2 and will be rated for everyone. Please note that this contest contains **at least one run-twice problem,** so please read the guide for [run-twice problems](https://codeforces.me/blog/entry/14799...
Fun fact: As far as [user:Evirir,2026-06-15] knows, this is the second round by Malaysians since, _Enjoy the contest, have fun solving, and we hope to see your name near the top of the standings!_

Full text and comments »

  • Vote: I like it
  • +324
  • Vote: I do not like it

276.
Kotlin Heroes 12 - Editorial
By BledDest, 17 months ago, In English
Kotlin Heroes 12 - Editorial The contest was prepared by [user:adedalic,2025-04-08], [user:awoo,2025-04-08], [user:Neon,2025-04-08] and me. We had a great team of testers: [user:shnirelman,2025-04-08], [user:ashmelev,2025-04-08], [user:FelixArg,2025-04-08], [user:KIRIJIJI,2025-04-08], [user:Alenochka,2025-04-08], [user:alyoks1,2025-04-08], [user:Vladosiya,2025-04-08], [user:mariibykova,2025-04-08] &mdash; huge thanks to all of you! <spoiler summary="One insane moment from the testing phase"> One day before the contest, [user:shnirelman,2025-04-08] completely destroyed problem H in less than 15 minutes. Thankfully, I had an idea of a replacement problem. </spoiler> Thanks to all competitors for participation, I hope you enjoyed the problems we made! And last but not least, I would like to express my gratitude to [user:MikeMirzayanov,2025-04-08] for keeping Codeforces and Polygon running even under unprecedented pressure from the bots. Okay, now for the editorial itself: [problem:2087A] Idea: [us...
~~~~~ fun main() { data class ModInt(val value : Int = 0) { val MOD = 998244353

Full text and comments »

  • Vote: I like it
  • +46
  • Vote: I do not like it

277.
Kotlin Heroes Episode 9 Editorial
By BledDest, 3 years ago, In English
Kotlin Heroes Episode 9 Editorial The contest was prepared by [user:awoo,2023-12-12], [user:Neon,2023-12-12], [user:adedalic,2023-12-12], [user:Roms,2023-12-12] and me. We are very grateful to all of the testers of the contest: [user:PavelKunyavskiy,2023-12-12], [user:I_Remember_Olya_ashmelev,2023-12-12], [user:vladmart,2023-12-12], [user:Vladosiya,2023-12-12] and [user:mariibykova,2023-12-12]. We hope you enjoyed both the problems and coding in Kotlin! Okay, now let's talk about how these problems can be solved: [problem:1910A] Idea: [user:BledDest,2023-12-12], preparation: [user:Neon,2023-12-12] <spoiler summary="Tutorial"> [tutorial:1910A] </spoiler> <spoiler summary="Solution (PavelKunyavskiy)"> ~~~~~ fun main() { repeat(readInt()) { println(readln().dropLastWhile { it == '0' }.dropLast(1)) } } private fun readInt() = readln().toInt() ~~~~~ </spoiler> [problem:1910B] Idea: [user:Roms,2023-12-12], preparation: [user:Roms,2023-12-12] <spoiler summary="Tutor...
private fun readInt() = readln().toInt() private fun readLongs() = readStrings().map { it.toLong

Full text and comments »

  • Vote: I like it
  • +35
  • Vote: I do not like it

278.
Educational Codeforces Round 107 Editorial
By awoo, history, 5 years ago, translation, In English
Educational Codeforces Round 107 Editorial [problem:1511A] Idea: [user:BledDest,2021-04-13] <spoiler summary="Tutorial"> [tutorial:1511A] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ fun main() { repeat(readLine()!!.toInt()) { readLine()!!.toInt() println(readLine()!!.split(' ').count { it != "2" }) } } ~~~~~ </spoiler> [problem:1511B] Idea: [user:BledDest,2021-04-13] <spoiler summary="Tutorial"> [tutorial:1511B] </spoiler> <spoiler summary="Solution (awoo)"> ~~~~~ for t in range(int(input())): a, b, c = map(int, input().split()) print("1" + "0" * (a - 1), "1" * (b - c + 1) + "0" * (c - 1)) ~~~~~ </spoiler> [problem:1511C] Idea: [user:BledDest,2021-04-13] <spoiler summary="Tutorial"> [tutorial:1511C] </spoiler> <spoiler summary="Solution (Neon)"> ~~~~~ #include <bits/stdc++.h> using namespace std; int main() { int n, q; scanf("%d%d", &n, &q); vector<int> a(n); for (int& x : a) scanf("%d", &x); while (q--)...
~~~~~ fun main() { repeat(readLine()!!.toInt()) { readLine()!!.toInt

Full text and comments »

  • Vote: I like it
  • +77
  • Vote: I do not like it

279.
Problems that I authored so far
By TheScrasse, history, 3 years ago, In English
Problems that I authored so far Hi everyone, after [contest:1854], maybe it's time to collect all my problems here. For now, I've mainly invented easy-ish problems. I wish to invent a very hard problem sooner or later :) <spoiler summary="Update after Pinely Round 3"> Done :D </spoiler> I'm putting the story of each problem under spoiler, because it may contain parts of the solution. I invented many problems by just trying random setups until I came up with something solvable, but some problems (especially the harder ones, for example [problem:1854D]) may have more interesting stories. Fun facts: - I struggled a lot to find a suitable div2A for [contest:1654]. I proposed a lot of problems that turned out to be unsuitable (for example, because they were too hard), then I used them somewhere else. - While I was writing this blog, I realized that [problem:1849E] is identical to my problem [preoii_allenamento \- Allenamento su ChinaForces](https://training.olinfo.it/#/task/preoii_allenamento/statement),...
Fun facts:

Full text and comments »

  • Vote: I like it
  • +75
  • Vote: I do not like it

280.
Educational Codeforces Round 81 Editorial
By awoo, history, 7 years ago, translation, In English
Educational Codeforces Round 81 Editorial [problem:1295A] Idea: [user:adedalic,2020-01-30] <spoiler summary="Tutorial"> [tutorial:1295A] </spoiler> <spoiler summary="Solution (BledDest)"> ~~~~~ t = int(input()) for i in range(t): n = int(input()) if(n % 2 == 1): print(7, end='') n -= 3 while(n > 0): print(1, end='') n -= 2 print() ~~~~~ </spoiler> [problem:1295B] Idea: [user:Roms,2020-01-30] <spoiler summary="Tutorial"> [tutorial:1295B] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ #include<bits/stdc++.h> using namespace std; typedef long long li; int n, x; string s; inline bool read() { if(!(cin >> n >> x >> s)) return false; return true; } inline void solve() { int ans = 0; bool infAns = false; int cntZeros = (int)count(s.begin(), s.end(), '0'); int total = cntZeros - (n - cntZeros); int bal = 0; for(int i = 0; i < n; i++) { if(total == 0) { if(bal == x) infAns = tru...
fun main() { val t = readLine()!!.toInt() for (tc in 1..t) { val (a, m, ~~~~~ fun gcd(a : Long, b : Long) : Long { return if (a == 0L) b else gcd(b % a, a) }fun

Full text and comments »

  • Vote: I like it
  • +106
  • Vote: I do not like it

281.
Educational Codeforces Round 91 Editorial
By awoo, history, 6 years ago, translation, In English
Educational Codeforces Round 91 Editorial [problem:1380A] Idea: [user:BledDest,2020-07-12] <spoiler summary="Tutorial"> [tutorial:1380A] </spoiler> <spoiler summary="Solution (Ne0n25)"> ~~~~~ #include <bits/stdc++.h> using namespace std; const int N = 1000; int n; int a[N]; void solve() { cin >> n; for (int i = 0; i < n; ++i) cin >> a[i]; for (int i = 1; i < n - 1; ++i) { if (a[i] > a[i - 1] && a[i] > a[i + 1]) { cout << "YES" << endl; cout << i << ' ' << i + 1 << ' ' << i + 2 << endl; return; } } cout << "NO" << endl; } int main() { int T; cin >> T; while (T--) solve(); } ~~~~~ </spoiler> [problem:1380B] Idea: [user:adedalic,2020-07-12] <spoiler summary="Tutorial"> [tutorial:1380B] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ fun main() { val winBy = mapOf('R' to 'P', 'S' to 'R', 'P' to 'S') repeat(readLine()!!.toInt()) { val s = readLine()!! val maxCnt = s.groupingBy { it }.eachCount().maxBy ...
~~~~~ fun main() { val winBy = mapOf('R' to 'P', 'S' to 'R', 'P' to 'S') repeat(readLine

Full text and comments »

  • Vote: I like it
  • +135
  • Vote: I do not like it

282.
Educational Codeforces Round 108 Editorial
By awoo, history, 5 years ago, translation, In English
Educational Codeforces Round 108 Editorial [problem:1519A] Idea: [user:adedalic,2021-04-30] <spoiler summary="Tutorial"> [tutorial:1519A] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ fun main() { repeat(readLine()!!.toInt()) { val (r, b, d) = readLine()!!.split(' ').map { it.toInt() } println(if (minOf(r, b) * (d + 1).toLong() >= maxOf(r, b)) "YES" else "NO") } } ~~~~~ </spoiler> [problem:1519B] Idea: [user:adedalic,2021-04-30] <spoiler summary="Tutorial"> [tutorial:1519B] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ fun main() { repeat(readLine()!!.toInt()) { val (n, m, k) = readLine()!!.split(' ').map { it.toInt() } println(if (n * m - 1 == k) "YES" else "NO") } } ~~~~~ </spoiler> [problem:1519C] Idea: [user:BledDest,2021-04-30] <spoiler summary="Tutorial"> [tutorial:1519C] </spoiler> <spoiler summary="Solution (awoo)"> ~~~~~ #include <bits/stdc++.h> #define forn(i, n) for (int i = 0;...
~~~~~ fun main() { repeat(readLine()!!.toInt()) { val (n, m, k) = readLine()!!.split

Full text and comments »

  • Vote: I like it
  • +92
  • Vote: I do not like it

283.
Educational Codeforces Round 127 Editorial
By awoo, history, 4 years ago, translation, In English
Educational Codeforces Round 127 Editorial [problem:1671A] Idea: [user:BledDest,2022-04-23] <spoiler summary="Tutorial"> [tutorial:1671A] </spoiler> <spoiler summary="Solution (BledDest)"> ~~~~~ t = int(input()) for i in range(t): s = input() ans = True n = len(s) for j in range(n): if (j == 0 or s[j] != s[j - 1]) and (j == n - 1 or s[j] != s[j + 1]): ans = False print('YES' if ans else 'NO') ~~~~~ </spoiler> [problem:1671B] Idea: [user:vovuh,2022-04-23] <spoiler summary="Tutorial"> [tutorial:1671B] </spoiler> <spoiler summary="Solution (vovuh)"> ~~~~~ for i in range(int(input())): n = int(input()) x = list(map(int, input().split())) print('YES' if x[-1] - x[0] - n + 1 <= 2 else 'NO') ~~~~~ </spoiler> [problem:1671C] Idea: [user:vovuh,2022-04-23] and [user:BledDest,2022-04-23] <spoiler summary="Tutorial"> [tutorial:1671C] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ fun main() { repeat(rea...
~~~~~ fun main() { repeat(readLine()!!.toInt()) { val (n, x) = readLine()!!.split

Full text and comments »

  • Vote: I like it
  • +70
  • Vote: I do not like it

284.
Invitation to NUS CS3233 Final Team Contest 2023 Mirror
By pooty, 3 years ago, In English
Invitation to NUS CS3233 Final Team Contest 2023 Mirror <img alt="logo" src="/predownloaded/7a/2d/7a2da3823042e763e0d15d6571ba0bcb38139f90.png" style="float: right;height: 100.0px;margin: 10.0px;max-width: 100.0%;max-height: 100.0%;"> Hello, Codeforces community! We are happy to invite you to participate in [National University of Singapore (NUS) CS3233 Final Team Contest 2023 Mirror](https://codeforces.me/contestInvitation/3d3b392eb92ff65022128f4e22462d5eaff55a25) on [Monday, April 10, 2023, at 09:35 UTC](https://www.timeanddate.com/worldclock/fixedtime.html?day=10&month=4&year=2023&hour=12&min=35&sec=0&p1=166). CS3233 is a course offered by NUS to prepare students in competitive problem solving. The contest is unofficial and will be held in Codeforces Gym. Standard ICPC rules **(Unrated, ICPC Rules, Teams Preferred)** apply. **The contest is unrated**. **Note the unusual starting time**. The problems are written and prepared by [user:user202729_,2023-04-08], [user:rama_pang,2023-04-08], and [user:pooty,2023-04-08]. We wo...
We hope you will enjoy and have fun in the contest. Good luck!

Full text and comments »

  • Vote: I like it
  • +276
  • Vote: I do not like it

285.
OCPC 2026 Winter — wrap
By adamant, history, 7 months ago, In English
OCPC 2026 Winter — wrap _If you are potentially interested in participating in OCPC **in person** in Summer/Autumn 2026, **please** fill **[this form](https://forms.gle/VdMRh6cAJRN4YvQN6)**!_ Hi everyone! <center><a href="https://ocpc.camp"><img src="https://ocpc.camp/images/ocpc_light.svg" height="80px"></a> <a href="https://icpc.foundation/"><img src="/predownloaded/43/08/43086529a28ccb5c9f2f2eec560ffa85e09c6881.svg" height="80px"></a></center> <center> <b>Supported by</b><br> <a href="https://www.janestreet.com/join-jane-street/open-roles/?type=students-and-new-grads&location=london"> <img src="/predownloaded/ee/f2/eef26616a3661c658d1545f18ed21fabb14d5871.svg" height="40px" style="margin: 10px 10px 10px 10px;"></a> <a href="https://www.hudsonrivertrading.com/"> <img src="https://ocpc.camp/images/HRT.svg" height="40px" style="margin: 10px 10px 10px 10px;"></a> <a href="https://www.silares.com/"> <img src="https://ocpc.camp/images/silares-red.svg" height="40px" style="margin: 10px 10px 10px ...
As usual, we did our best to ensure that onsite participation is not only educational, but alsofun

Full text and comments »

  • Vote: I like it
  • +157
  • Vote: I do not like it

286.
Invitation to CodeChef July CookOff 2021 (with prizes!)
By Ashishgup, 5 years ago, In English
Invitation to CodeChef July CookOff 2021 (with prizes!) We invite you to participate in CodeChef’s [July Cookoff](https://www.codechef.com/COOK131?utm_source=codeforces_blog&utm_medium=organic&utm_campaign=JulyCook), today &mdash; 28th July, from [8:00 PM &mdash; 10:30 PM IST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=July+Cook-off+2021&iso=20210728T2000&p1=44&ah=2&am=30). **Note the unusual time**. There will be **7 problems** in all divisions. The contest will be rated for all three Divisions. The July Cook-Off also marks the launch of our new prize structure for global & Indian participants. More details are given below. Joining us on the problem setting panel are: - Contest Admins: Ashish [user:ashishgup,2020-12-19] Gupta and Jatin [user:jtnydv25,2021-05-30] Yadav - Head Admin: Alex [user:Um_nik,2021-06-26] Danilyuk - Tester: Aryan [user:aryanc403,2021-07-28] Choudhary - Statement Verifier: Riley [user:1-gon,2021-07-28] Borgard - Editorialist: Vichitr [user:Vichitr,2021-07-28] Gandas, Srikkanth [u...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +163
  • Vote: I do not like it

287.
Educational Codeforces Round 116 Editorial
By awoo, history, 5 years ago, translation, In English
Educational Codeforces Round 116 Editorial [problem:1606A] Idea: [user:BledDest,2021-10-30] <spoiler summary="Tutorial"> [tutorial:1606A] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ fun main() { repeat(readLine()!!.toInt()) { val s = readLine()!! println(s.last() + s.substring(1)) } } ~~~~~ </spoiler> [problem:1606B] <spoiler summary="Tutorial"> [tutorial:1606B] </spoiler> <spoiler summary="Solution (Neon)"> ~~~~~ #include <bits/stdc++.h> using namespace std; using li = long long; int main() { ios_base::sync_with_stdio(false); cin.tie(NULL); int t; cin >> t; while (t--) { li n, k; cin >> n >> k; li ans = 0, cur = 1; while (cur < k) { cur *= 2; ++ans; } if (cur < n) ans += (n - cur + k - 1) / k; cout << ans << '\n'; } } ~~~~~ </spoiler> [problem:1606C] Idea: [user:BledDest,2021-10-30] <spoiler summary="Tutorial"> [tutorial:1606C] </spoiler> <spoiler summary="S...
~~~~~ fun main() { repeat(readLine()!!.toInt()) { val s = readLine

Full text and comments »

  • Vote: I like it
  • +99
  • Vote: I do not like it

288.
Educational Codeforces Round 145 Editorial
By awoo, history, 3 years ago, translation, In English
Educational Codeforces Round 145 Editorial [problem:1809A] Idea: [user:BledDest,2023-03-24] <spoiler summary="Tutorial"> [tutorial:1809A] </spoiler> <spoiler summary="Solution (Neon)"> ~~~~~ #include <bits/stdc++.h> using namespace std; int main() { ios::sync_with_stdio(false); cin.tie(0); int tc; cin >> tc; while (tc--) { string s; cin >> s; vector<int> cnt(10); for (auto c : s) ++cnt[c - '0']; int mx = *max_element(cnt.begin(), cnt.end()); if (mx == 4) cout << -1; else if (mx == 3) cout << 6; else cout << 4; cout << '\n'; } } ~~~~~ </spoiler> [problem:1809B] Idea: [user:BledDest,2023-03-24] <spoiler summary="Tutorial"> [tutorial:1809B] </spoiler> <spoiler summary="Solution 1 (adedalic)"> ~~~~~ fun main() { repeat(readln().toInt()) { val n = readln().toLong() var l = (-1).toLong() var r = 1e9.toLong() while (r - l > 1) { val mid = (l + r) / 2 if (mid * mid >=...
fun main() { repeat(readln().toInt()) { val n = readln().toLong() var ans

Full text and comments »

  • Vote: I like it
  • +139
  • Vote: I do not like it

289.
Codeforces Round #621 (Div. 1 + Div. 2)
By FieryPhoenix, 7 years ago, In English
Codeforces Round #621 (Div. 1 + Div. 2) Moo! (Hello Codeforces!) I’m very excited to invite you to [contest:1307], which will take place on [contest_time:1307]. In this round, you will be helping Farmer John and his prized cow Bessie cowmplete some fun tasks. The contest will have **7 problems** and is **combined and rated for both divisions**. The duration is **2 hours and 15 minutes**. The problems are prepared by me ([user:FieryPhoenix,2020-02-15]) and [user:dragonslayerintraining,2020-02-15]. We tried very hard to make them interesting and hope that you will enjoy them too! This round would not have been possible without the wonderful coordination by [user:adedalic,2020-02-15] and [user:cdkrot,2020-02-15]. Thank you so much to the testers as well for all the invaluable advice: [user:tmwilliamlin168,2020-02-15], [user:walnutwaldo20,2020-02-15], [user:nikolapesic2802,2020-02-15], [user:bfs.07,2020-02-15], [user:Rods,2020-02-15], [user:lynmisakura,2020-02-15], [user:JustasLe,2020-02-15], and [user:hocky,2020-02-...
Good luck and more importantly, have fun and learn something new!

Full text and comments »

  • Vote: I like it
  • +547
  • Vote: I do not like it

290.
Codeforces Round 958 (Div. 2)
By feecIe6418, history, 2 years ago, In English
Codeforces Round 958 (Div. 2) Hello Codeforces! I am glad to invite you to [contest:1988] which will start on [contest_time:1988]. The contest will last for 2 hours with 6 tasks for you to solve. The contest will only be rated for those with a rating not higher than 2099, but high-rated competitive programmers are also more than welcome to participate out of competition. The score distribution is: 500-1000-1000-2000-2500-3500 The contest will be impossible without the help from: - [user:244mhq,2024-07-13] for wonderful coordination. - [user:gyh20,2024-07-13], [user:Dominater069,2024-07-13], [user:Um_nik,2024-07-13], [user:A_G,2024-07-13], [user:omeganot,2024-07-13], [user:tkl2006,2024-07-13], [user:harsh__h,2024-07-13], [user:oursaco,2024-07-13], [user:Hori,2024-07-13], [user:kostia244,2024-07-13], [user:ishaandas1,2024-07-13], [user:maomao90,2024-07-13], [user:waidenf,2024-07-13], [user:Stefan2417,2024-07-13], [user:MisterReaper,2024-07-13] for testing. - [user:MikeMirzayanov,2024-07-13] for Code...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +392
  • Vote: I do not like it

291.
Invitation to CodeChef December Cook-Off 2020
By Ashishgup, 6 years ago, In English
Invitation to CodeChef December Cook-Off 2020 We invite you to participate in CodeChef’s [December Cook-Off](https://bit.ly/COOK125-Codeforces), this **Monday, 21st December**, from [9:30 PM to 12:00 AM IST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=December+2020+Cook-Off&iso=20201221T2130&p1=44&ah=2&am=30). <br> **Note the unusual time**. You will be given a total of **9 problems** (7 in Div2, 7 in Div1) to solve in a duration of **2.5 hours**. Joining us on the problem setting panel are: - Setters: Utkarsh [user:Utkarsh.25dec,2020-12-19] Gupta, Jeevan [user:JeevanJyot,2020-12-19] Jyot Singh, Bhavyesh [user:bhvdsi,2020-12-19] Desai, David [user:ki0apa,2020-12-19] Horne, Vitaly [user:Bugman,2020-12-19] Demidenko, Pranav [user:ExplodingFreeze,2020-12-19] Rajagopalan, Andrzej [user:Okrut,2020-12-19] Turko - Tester: Rahul [user:amnesiac_dusk,2020-12-19] Dugar - Statement Verifier: Jakub [user:Xellos,2020-12-19] Safin - Editorialist: Rajarshi [user:RestingRajarshi,2020-12-19] Basu - Video Editor...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +173
  • Vote: I do not like it

292.
Brazilian Bizarre Adventures at the TST
By defnotmee, history, 4 years ago, In English
Brazilian Bizarre Adventures at the TST Hello codeforces! I was reminiscing about the brazilian TST that just happened and figured it was way too crazy not to share with everyone how it went. So as a follow up to [this blog](https://codeforces.me/blog/entry/109950) I'll be going through my experiences at the event. Get ready for a ride, because this is gonna be a long one. Day of Arrival: Coming out of the closet ------------------ The people of my school all gathered in a bus to go to the hotel we were staying at. That bus made a beeping noise every time we passed 90 km/h, and considering we were travelling at night, we were hearing that noise way too often! While in the ride, I stole [user:LFFB_,2022-12-11]'s laptop and started playing Osu on it. Even though I was playing on the touchpad and the bus was bumping around, I was able to clutch out an S on "Pepsi Man", which was quite a challenge despite being on relax mode. ![ ](https://media.discordapp.net/attachments/1049687529298866216/1051480070755201107/indi...
/Chicken_fight). We would constantly change our pairs around and it was super superfun.

Full text and comments »

  • Vote: I like it
  • +279
  • Vote: I do not like it

293.
Codeforces Round #815 (Div. 2)
By TeaTime, 4 years ago, In English
Codeforces Round #815 (Div. 2) Hello, Codeforces! We are proud to finally invite you to participate in [Codeforces Round #815 (Div. 2)](https://codeforces.me/contest/1720), which will start on [contest_time:1720]. You will be given **5** problems, one of which contains a subtask and **2** hours to solve them. We greatly encourage you to read all the problems. Round is completely set by SIS (Summer Informatics School) students. During the camp our students did their best to prepare interesting and creative problems. You can check previous rounds prepared by SIS students: [Codeforces Round #612](https://codeforces.me/contests/1286,1287), [Codeforces Round #530](https://codeforces.me/contests/1098,1099), [Codeforces Round #694](https://codeforces.me/contests/1471,1470). People who participated in the creation of the round: - Problems are authored and prepared by: Kirill [user:kirill.kligunov,2022-08-16] Kligunov, Gleb [user:zer0brain,2022-08-16] Ustimenko, Alexey [user:Allvik06,2022-08-16] Vasi...
Good luck & have fun!

Full text and comments »

  • Vote: I like it
  • +251
  • Vote: I do not like it

294.
Codeforces Round 1093 (Div. 1, Div. 2)
By misteg168, history, 5 months ago, In English
Codeforces Round 1093 (Div. 1, Div. 2) Hola Codeforces! We are really excited to invite you to participate in [Codeforces Round #1093 (Div. 1)](https://codeforces.me/contest/2219) and [Codeforces Round #1093 (Div. 2)](https://codeforces.me/contest/2220), which will be held on [contest_time:2219]. For division 1, you will be given **2 hours** to solve **5 problems**, for division 2, you will be given **2 hours** to solve **6 problems**. Note that at least one of the problems will be divided into subtasks. Furthermore, at least one problem may be interactive, so please [read the guide for interactive problems](https://codeforces.me/blog/entry/45307) if you are not familiar with them. The scoring distribution will be announced later. The problems were authored and prepared by [user:misteg168,2026-04-11], [user:danx,2026-04-11], [user:rlidon2006,2026-04-11], and [user:Misuki,2026-04-11]. We would really like to thank the following people for making this round possible: [user:mhq,2026-04-11] for his orz coor...
We wish you all an exciting experience. Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +213
  • Vote: I do not like it

295.
Codeforces Round #493
By cdkrot, history, 8 years ago, translation, In English
Codeforces Round #493 Hi, codeforces! I am happy to invite you to the codeforces round #493, which happens at [contest_time:997]. This round writers are &mdash; Ildar [user:300iq,2018-06-30] Gainullin, Grigory [user:gritukan,2018-06-30] Reznikov, Mike [user:MikeMirzayanov,2018-06-30] Mirzayanov, and me, [user:_kun_,2018-06-30]. Big thanks for people, who tested round &mdash; Shiqing [user:cyand1317,2015-05-01] Lyu, Andrew <a class="rated-user user-green" href="/profile/GreenGrape" title="Finally Green GreenGrape">GreenGrape</a> Rayskiy, Ivan [user:isaf27,2018-06-30] Safonov, Alexey [user:aleks5d,2018-06-30] Upirvitsky. Also thanks to Mike [user:MikeMirzayanov,2018-06-30] Mirzayanov and Nikolay [user:KAN,2018-06-30] Kalinin for help with round preparation. And to Mike [user:MikeMirzayanov,2018-06-30] Mirzayanov for codeforces and polygon systems. Traditionally, there will be 5 problems for 2 hours. I hope you will enjoy the problemset, good luck and have fun! Scoring distribution will be pu...
luck and have fun!

Full text and comments »

  • Vote: I like it
  • +274
  • Vote: I do not like it

296.
Invitation to Baozii Cup 3
By __baozii__, history, 8 months ago, In English
Invitation to Baozii Cup 3 Hello, Codeforces! We are happy to invite you Baozii Cup 3, which will take place on [contest_time:664651]. You will have $5$ hours to solve $13$ problems, including **at least one** interactive problem. This is a team contest following ACM/ICPC rules, with teams of up to $3$ members. The penalty for an incorrect submission is $20$ minutes. The standings will be frozen for the last $60$ minutes of the contest. Most problems are created and prepared by me, with help from [user:Bronya_H,2026-01-17], [user:zeemanz,2026-01-17], and [user:TRDOG,2026-01-17]. We would like to thank: - [user:MikeMirzayanov,2026-01-17] for creating the fantastic CodeForces and Polygon platform. - [user:Sserxhs,2026-01-17], [user:SATSKY_2025target_LGM,2026-01-17], [user:-WIDA-,2026-01-17], [user:fatalerror,2026-01-17], and [user:itsiftikar02,2026-01-17] for testing the round and providing valuable feedback. - [user:-firefly-,2026-01-17] for generously letting me copy his [Soy Cup #2: ...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +113
  • Vote: I do not like it

297.
MIT Informatics Tournament 2025 Spring Invitational
By antontrygubO_o, 18 months ago, In English
MIT Informatics Tournament 2025 Spring Invitational **Update (5/8):** The Finals Round has concluded (here are links to [gym](https://codeforces.me/gym/105870/standings) & [editorial](https://codeforces.me/gym/105870/attachments/download/31412/MITIT_2025_Finals_Editorial.pdf)). Editorials and problems for [Qualification Round 1](https://codeforces.me/gym/105822) and [Qualification Round 2](https://codeforces.me/gym/105837) are in the gym. Congratulations to all of our finalists! 1. [user:hos.lyric,2025-05-09] (405, 13:32:43) &mdash; $1500 2. [user:tourist,2025-05-09] (400, 05:50:33) &mdash; $1000 3. [user:benq,2025-05-09] (340, 05:41:11) &mdash; $500 4. [user:A_G,2025-05-09] (310, 05:52:27) 5. [user:Kevin114514,2025-05-09] (310, 09:29:36) 6. [user:ksun48,2025-05-09] (305, 06:32:42) 7. [user:gamegame,2025-05-09] (305, 06:51:14) 8. [user:rainboy,2025-05-09] (305, 07:16:58) 9. [user:jeroenodb,2025-05-09] (300, 04:57:25) 10. [user:errorgorn,2025-05-09] (300, 05:51:34) 11. [user:ecnerwala,2025-05-09] (300, 05:53:09) 12. ...
day of the Final Round is filled with exciting activities such as fun tours around Boston, a fancy

Full text and comments »

  • Vote: I like it
  • +199
  • Vote: I do not like it

298.
India ICPC — Amritapuri 2020 Regionals
By kshitij_sodani, history, 5 years ago, In English
India ICPC — Amritapuri 2020 Regionals Hi Codeforces! <b>ICPC Amritapuri 2020 Regional Round<b> will be held on [Codedrills](https://codedrills.io/contests/icpc-amritapuri-2020-regional-round) tomorrow. ![ ](https://i.imgur.com/AwOXmHA.png) <b>Contest Details<b> - Contest Link — [ICPC Amritapuri 2020 Regional Round](https://codedrills.io/contests/icpc-amritapuri-2020-regional-round) - Date & Time — 14 August 2021, Saturday, 18:00 IST - Duration — <b>4<b> Hours - There is a ranklist freeze of 60 minutes. Ranklist will freeze at 21:00 IST. - There will be 10-13 problems to solve - Will follow standard ICPC scoring system (20 minutes penalty and 1 point per problem) - The problems may not be sorted by difficulty <b> Selection Criteria - Top few teams will advance to World Finals <b>Clarifications<b> - Only ask the clarifications about the problems by messaging the [private clarification group via discuss](https://discuss.codedrills.io/g/clarifications). - Do not ask any doubts about the problem...
Good luck Have Fun! Hope you like the problems!

Full text and comments »

  • Vote: I like it
  • +224
  • Vote: I do not like it

299.
Codeforces Round 1114 (Div. 3)
By yse, 5 weeks ago, In English
Codeforces Round 1114 (Div. 3) Hello, Codeforces! ------------------ I am very excited to invite you to participate in [contest:2254], which will take place on [contest_time:2254]. You will be given $2$ hours and $15$ minutes to solve $7$ problems, where one problem will be split into subtasks. All problems were authored and prepared by me. The round will be hosted by rules of educational rounds (extended ICPC). Thus, all solutions will be judged on preliminary tests during the round, and after the round, there will be a 12-hour phase of **open hacks**. After the open hack phase, all accepted solutions will be rejudged on successful hacks. Also, note that there is no score distribution but the usual penalty of **10 minutes** for each wrong submission, following the rules of educational rounds. [Remember](https://codeforces.me/blog/entry/59228) that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure fo...
Good luck, and most importantly, have fun!

Full text and comments »

  • Vote: I like it
  • +212
  • Vote: I do not like it

300.
Codeforces Round #754 (Div. 2) Editorial
By ExplodingFreeze, 5 years ago, In English
Codeforces Round #754 (Div. 2) Editorial Thank you for participating! We hope you enjoyed the contest. [problem:1605A] Authored and prepared by [user:JeevanJyot,2021-11-12] <spoiler summary="Hint 1"> What happens to the value of $d(a_1, a_2, a_3)$ if you perform an operation on $a_1$ and $a_3$? </spoiler> <spoiler summary="Hint 2"> What happens if you perform an operation on $a_1$ and $a_2$? </spoiler> <spoiler summary="Hint 3"> Can we use negative values to improve the worst answer? </spoiler> <spoiler summary="Solution"> [tutorial:1605A] </spoiler> <spoiler summary="Solution [c++] (JeevanJyot)"> ~~~~~ #include <bits/stdc++.h> using namespace std; int32_t main() { ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); int T; cin >> T; while(T--) { int a, b, c; cin >> a >> b >> c; cout << ((a + c - 2 * b) % 3 == 0 ? 0 : 1) << "\n"; } return 0; } ~~~~~ </spoiler> <spoiler summary="Solution [Kotlin] (ExplodingFreeze...
fun mod_inv(base: Int, MOD: Int): Long { return mod_expo(base, MOD - 2, MOD) }

Full text and comments »

  • Vote: I like it
  • +202
  • Vote: I do not like it

301.
CodeChef September CookOff 2021 (with prizes and new admins!)
By Ashishgup, 5 years ago, In English
CodeChef September CookOff 2021 (with prizes and new admins!) We invite you to participate in CodeChef’s [September Cookoff](https://www.codechef.com/COOK133), today &mdash; 19th September from [9:30 PM &mdash; 12:30AM IST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=September+Cook-off+2021&iso=20210919T2130&p1=44&ah=3&am=00). The contest will be **3 hours long**. There will be **7 problems** in Div 1/2 and **8 problems** in Div 3. It will be rated for all three Divisions. Joining us on the problem setting panel are: - Contest Admins: Ashish [user:ashishgup,2020-12-19] Gupta and Anton [user:antontrygubO_o,2021-09-19] Trygub - Head Admin: Alex [user:Um_nik,2021-06-26] Danilyuk - Tester: Anshu [user:_runtimeTerror_,2021-09-19] Garg - Setters: [user:abc864197532,2021-09-19], Ashish [user:ashishgup,2021-09-19] Gupta, Utkarsh [user:Utkarsh.25dec,2021-09-19] Gupta, Rahim [user:Nots0fast,2021-09-19] Mammadli, [user:flamestorm,2021-09-19], Anirudh Krishna, Chaithanya [user:Dragonado,2021-09-19] Shyam, Amruth [user:amruth_...
Good luck and have fun!

Full text and comments »

  • Vote: I like it
  • +150
  • Vote: I do not like it

302.
Dynamic connectivity problem
By adamant, 12 years ago, translation, In English
Dynamic connectivity problem Hi everyone! Recently, at the MIPT: The Fall training camp on the contest from Alexander [user:Milanin,2014-11-22] was a problem from Petr Mitrichev Contest 7. We were given a graph and a set of queries like "suppose we removed from the graph $k \leq 4$ edges. Check whether graph is still connected?" I want to talk further about the solution of a more general problem, when the edges are added and removed without additional constraints in $O (k \log k)$ offline. The first algorithm with such an assessment was offered by David Eppstein in 1992, reducing it to fully dynamic minimum spanning tree problem, but here we will focus on a simple algorithm, proposed in 2012 by Sergei [user:Burunduk1,2014-11-22] Kopeliovich. [cut]<br> Let's assume that there are three types of queries & mdash; add the edge (`+`), remove the edge (`-`) and find out some information about the graph (`?`) (in this case, let it be the number of connected components of the graph). We assume that we received a...
for this was made [training](/gym/100551). Good Luck & Have Fun!

Full text and comments »

  • Vote: I like it
  • +141
  • Vote: I do not like it

303.
Stop Looking at Standings
By tryingoutcp, history, 8 months ago, In English
Stop Looking at Standings Story Time ------------------ It's been about a year since I started CP and reached Expert pretty fast. However, for some reason or the other, I couldn’t reach CM. I got pretty close multiple times but lost rating as soon as I was one contest away. It felt like I was collecting every 18xx rating lmao. ![LoL](/predownloaded/73/b3/73b30cc6f51728448c82e0c2d02b44b6aedb0255.png) At least in the beginning, the reason I wasn’t CM was, well, I genuinely wasn’t at that level yet. However, towards the end of the year, I felt like I was of that strength, but for some reason couldn’t convert that into the rating jump I needed. I think some of you would be able to relate to this &mdash; you feel stronger than your current rating, but can’t reach there, and maybe there’s something holding you back psychologically. Beating Psychological Pressure During a Contest ------------------ I tried to do something different in the last 2 contests I wrote to deal with pressure. Firstly, I stopped...
that. Trust the process, and have fun solving problems and learning new things. That’s enough :)

Full text and comments »

  • Vote: I like it
  • +364
  • Vote: I do not like it

304.
Will competitive programming ever become a real sport?
By TeaPot, history, 9 years ago, In English
Will competitive programming ever become a real sport? I always was dreaming that one day competitive programming will become a real sport, not just activity for a small group of participants. Why? Because I don't really like working and my tries to do some science were totally unsuccessful. It would be cool to live just by doing what you like. Very childish, I know. But this blog is not about if competitive programming is important or are there any ways to make it interesting to watch to wider audience. I am just trying to understand, is it currently moving toward real sport or away from it? And I get some mixed signals about that: Bad signals: - Big onsites (like GCJ or TCO) seem to cut the number of participants and the amount of prizes. - Some onsite-finals are turning to online-finals. For example, several years ago we had Russian Code Cup onsite in Russia, currently RCC Finals is online. - Some big companies are turning away from sport programming (IBM is stopping sponsorship of ACM ICPC). Good signals: - Some ne...
will it forever be just for fun and for students to get to the interview in a big company?

Full text and comments »

  • Vote: I like it
  • +669
  • Vote: I do not like it

305.
Basis change in linear recurrences
By adamant, history, 4 years ago, In English
Basis change in linear recurrences Hi everyone! Today I'd like to write about Fibonacci numbers. Ever heard of them? Fibonacci sequence is defined as $F_n = F_{n-1} + F_{n-2}$. It got me interested, what would the recurrence be like if it looked like $F_n = \alpha F_{n-p} + \beta F_{n-q}$ for $p \neq q$? <hr> **[Timus &mdash; Fibonacci Sequence](https://timus.online/problem.aspx?space=1&num=1133)**. The sequence $F$ satisfies the condition $F_n = F_{n-1} + F_{n-2}$. You're given $F_i$ and $F_j$, compute $F_n$. <hr> Using $L(x^n) = F_n$ functional, we can say that we essentially need to solve the following system of equations: $$1 \equiv \alpha x^{-p} + \beta x^{-q} \pmod{x^2-x-1}.$$ To get the actual solution from it, we should first understand what exactly is the remainder of $x^n$ modulo $x^2-x-1$. The remainder of $P(x)$ modulo $(x-a)(x-b)$ is generally determined by $P(a)$ and $P(b)$: $$ P(x) \equiv r \mod(x-a)(x-b) \iff \begin{cases}P(a) = r,\\ P(b)=r.\end{cases} $$ Therefore, our equation a...
P. S. you can also derive it from Fibonacci matrix representation, but this way is much morefun

Full text and comments »

  • Vote: I like it
  • +172
  • Vote: I do not like it