[Tutorial] Matroid intersection in simple words **[This article is also available in [Russian](https://codeforces.me/blog/entry/69287?locale=ru)]** Hello, CodeForces. I think that matroids are beautiful and powerful concept, however, not really well known in competitive programming. I’ve discovered matroids at 2019 Petrozavodsk Winter Training Camp. There was a problem that clearly cannot be solved using usual techniques I knew, editorial for this problem was just these three words “just matroid intersection”. Back then it took me more than 2 days of upsolving to find all the information and details I need and implement solution that gets Accepted on this. And it took way longer to actually understand why does it work and exactly how does it work. (I still hesitate in some details.) Of course, it is not hard to google up all the definitions and some related articles, but in my opinion they all are focused more on mathematical part of theory, strict proofs in some not really obvious but short ways, and observing only ke...

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Catching the Mole II(Hard Version) (Psychotic_D cheating case aftermath) This is a part 2 of [my other blog](https://codeforces.me/blog/entry/131821) on the [user:Psychotic_D,2024-07-23] situation. I highly recommend you see it before this one for context. If you don't care that much, here is a quick recap of what was covered in the other blog before we get started: [user:Psychotic_D,2024-07-23] had a ridiculously good performance on his friend's ([user:wuhudsm,2024-07-23]) round. This let many people become suspicious of whether he achieved this legitimately. Then multiple accusations were thrown around and I did my blog doing my own investigation and compiling the most compelling evidence I found. The takeaway was that [user:Psychotic_D,2024-07-23] was probably cheating along [user:EndlessDreams,2024-07-23], who would give him code for [user:Psychotic_D,2024-07-23] to copy. [user:Psychotic_D,2024-07-23] would alter them heavily to avoid plagiarism, but it was clear beyond a reasonable doubt that he was cheating. Well, I finished writing that blog, ...

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Apology for faults in Codeforces Round 1098 Hello, I'm Sanae. In ufc+8 zone, I watched the entire contest at midnight. Too many cheaters emerged and we were busy banning them. I noticed WA submissions on [problem:2228B], [problem:2228C2] and TLE submissions on [problem:2228D], which was intended. Soon after the end of the contest, I released the editorial. The bad news was, the complaints flooded the website and my contribution fell from +91 to -92. After reflecting on the issues, I was anixous and blamed myself. Now, I make an apology to point out the problems to avoid them next time. Sorry, everyone! 1. Too many cheaters emerged. [Comment 1](https://codeforces.me/blog/entry/153617?#comment-1365371) 2. The problems stay in the queue for a very long time bothered contestants. 3. B is easy but many contestants misssed the corner case. And C has many corner cases. [Comment 1](https://codeforces.me/blog/entry/153617?#comment-1365212), [Comment 2](https://codeforces.me/blog/entry/153617?#comment-1365256), [Comment 3...

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Osijek Competitive Programming Camp 2023 winter — wrap Hi everyone! <center><a href="https://ocpc.mathos.unios.hr"><img src="https://ocpc.mathos.unios.hr/images/ocpc.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://www.think-cell.com/osijek2023"><img src="/predownloaded/97/88/97887beeb75a4601259414b36ecee0160c29d027.svg" height="40px" 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> </center> The [Osijek competitive programming camp](https://ocpc.mathos.unios.hr) (also see the [announcement](https://codeforces.me/blog/entry/110945) on Codeforces) just concluded last Sunday, on February 26, and I'd lik...

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Avito Code Challenge 2018 Hi! I'm glad to invite you to take part in [contest:981] which starts on [contest_time:981]. Any participant can join the round and it will be rated for each participant. Hope to see you among the participants! Problems are prepared by me — Ildar Gainullin. This round is conducted on the initiative and support of [Avito](https://www.avito.ru/). Avito.ru is a Russian classified advertisements website with sections devoted to general good for sale, jobs, real estate, personals, cars for sale, and services. Avito.ru is the most popular classifieds site in Russia and is the third biggest classifieds site in the world after Craigslist and the Chinese website 58.com. Many thanks to Vladislav [user:winger,2018-05-24] Isenbaev, Grigory [user:gritukan,2018-05-24] Reznikov, Ivan [user:isaf27,2018-05-24] Safonov，Alexander [user:AlexFetisov,2018-05-24] Fetisov and Shiqing [user:cyand1317,2018-05-24] Lyu for the round testing, Nikolay [user:KAN,2018-05-24] Kalinin for helping me to...

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Problem Topics Good Day to you! I've been asked to make some topic-wise list of problems I've solved. Even though I couldn't involve all problems, I've tried to involve at least "few" problems at each topic I thought up (I'm sorry if I forgot about something "easy"). I've alredy made such list once anyway I've tried to include more problems now &mdash; so here it is: <spoiler summary="aho"> http://www.spoj.com/problems/ADAJOBS/ URI 2226 (5) //[NICE][NUMBERS][DP] http://www.spoj.com/problems/SUB_PROB/en/ http://codeforces.me/contest/696/problem/D 8 http://www.spoj.com/problems/AHOCUR/ 5 //Aho-Corassic + DP https://www.codechef.com/problems/LYRC (5) //Sample aho-brute-force http://codeforces.me/problemset/problem/346/B //Proposed by [user:bradyawn,2019-08-03] </spoiler> <spoiler summary="automat"> 6861 [LA] //CYK UVA 10679 //Suffix Automat http://www.spoj.com/problems/STRMATCH/ //Suffix Automat &mdash; trie might do too http://www.spoj.com/problems/NSUBST...

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Educational Codeforces Round 92 [Rated for Div. 2] Hello Codeforces! On [contest_time:1389] [contest:1389] will start. Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.me/blog/entry/51208">blog post</a>. 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 will have access to copy any solution and test it locally. You will be given **6 or 7 problems** and **2 hours** to solve them. The problems were invented and prepared by Roman [user:Roms,2020-07-28] Glazov, Adilbek [user:adedalic,2020-07-28] Dalabaev, Vladimir [user:vovuh,2020-07-28] Petrov, Ivan [us...

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Report: Contest-Time Solution Hints Linked to NotOnlySuccess I am writing this blog to report a competitive-integrity issue involving the Codeforces user [user:NotOnlySuccess,2026-08-09] and a website associated with their content. The main issue is simple: **problem-specific solution material and hints for an ongoing Codeforces contest were made available before the contest ended.** # 1. Solution material published before the contest ended During [Codeforces Round 1116 (Div. 1, Div. 2)](https://codeforces.me/blog/entry/155668), an article titled [CF Round 1116 (Div. 1+2)](https://mp.weixin.qq.com/s/P3QJqmQFRsLlW9GX_y_8YQ) was published on a WeChat public account at August 10, 2026, 00:37 (UTC +8). The Codeforces contest ended at August 10, 2026, 01:05 (UTC +8). Therefore, the article was publicly available **28 minutes before the contest ended**.  The article already contained problem-specific solution material. For readers who do not understand Chinese...

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OCPC 2025 Winter — wrap Hi everyone! <center><a href="https://ocpc.camp"><img src="https://ocpc.camp/images/ocpc.svg" height="100px"></a> <a href="https://icpc.foundation/"><img src="/predownloaded/43/08/43086529a28ccb5c9f2f2eec560ffa85e09c6881.svg" height="100px"></a></center> <center> <b>Supported by</b><br> <a href="https://www.quantco.com/"><img src="https://ocpc.camp/images/quantco.svg" height="60px" style="margin: 10px 10px 10px 10px;"></a> <a href="https://ordercapital.com/"> <img src="https://ocpc.camp/images/OrCa.svg" height="60px" style="margin: 10px 10px 10px 10px;"> </a> <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="60px" style="margin: 10px 10px 10px 10px;"></a> <a href="https://pinely.com/"> <img src="/predownloaded/0a/0f/0a0f3f67435d1f6e467bc7203d4a2090ba8f92cc.svg" height="60px" style="margin: 10px 10px 10px 10px;"></a> </ce...

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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, ...

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Top228 of comments with too negative feedback At one warm winter day I've said to my mother, that I'm going to drink with my friends, but I fooled her: actually I decided to go to a gym. Unfortunately it was closed. I was so sad about it and didn't know what to do: I couldn't return home, because if my mother only knew that I spend my time doing sports she would never give money for buying Jaguar! That's why I went to the nearest padik, turned on russian rap on my mobile phone and started to read some fresh blogs on Codeforces. It was such attractive occupation that I walked to blog of [user:Amir.bh,2015-01-25] with top100 best comments in English. I was greatly inspired by it and I found that this idea is not fully realized. So, it leads me to take one more cup of yazhka. And after that I made this rate. Top 228 comments with negative feedback: <b>1</b>: -600 [user:kursatbakis0,2015-01-24] http://codeforces.me/blog/entry/13997#comment-189443 <b>2</b>: -271 [user:Makkar,2015-01-24] http://codeforces.me/blog/entry/9907...

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Exposing Mass cheating in today's Div(1+2) And last Div2 round Last time, I was talking about Abhipsita Das, who is the head of Indian cheaters. After my series of blogs was taken down and I received no reply to my personal messages regarding this from any officials, I am now showing you some solutions that have not been addressed so far. These codes are from Abhipsita Das <spoiler summary="Sample images of 1989C : Two Movies"> <spoiler summary="1">  </spoiler> <spoiler summary="2">  </spoiler> <spoiler summary="3">  </spoiler> <spoiler summary="4">  </spoiler> <spoiler summary="5">  </spoiler> <spoiler summary="6"> ![ ](/predownloaded/07/fc/07fca9f5fd08539a...

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Canada Cup <div style="float:right;margin:0 1em 1em 1em;"><a href="https://diagram.ca/"><img src="http://codeforces.me/predownloaded/60/1a/601ad2651390b1ff2232c003a354c60ac059d570.png"/></a></div> Hi Codeforces, I'm excited to announce the Canada Cup, the first Codeforces contest to be sponsored by <a href="https://diagram.ca/">Diagram</a>! This is a rated Codeforces round (with T-shirts!) for both divisions which will take place on <a href="http://www.timeanddate.com/worldclock/fixedtime.html?day=22&month=10&year=2016&hour=18&min=0&sec=0&p1=166">October 22 at 11:00am EDT</a>. <b>Although the contest is organized in Canada, all competitors worldwide will be able to compete and win prizes.</b> The problems for this round were written me ([user:zxqfl,2016-10-15]) and the Codeforces team. I'd like to thank: - My coauthors for contributing great problems to the round - [user:GlebsHP,2016-10-15] for his help in preparation - [user:MikeMirzayanov,2016-10-15] for creating Codeforce...

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IOI 2017, первый тур <center><a style="font-size:20pt;" href="http://scoreboard.ioi2017.org/Ranking.html">Таблица результатов</a></center> <spoiler summary="Краткий обзор задач"> [Nowruz](http://jonathanirvin.gs/files/ioi2017/day1/nowruz-ISC.pdf) &mdash; это первая со времён канадского maze в 2010 году задача на IOI с открытыми тестами. Забавный факт состоит в том, что nowruz, как и maze, это задача про клетчатый лабиринт. Дано клетчатое поле, в котором некоторые клетки свободны, и нужно оставить от них связное подмножество клеток, образующее дерево (в том смысле, что от любой клетки до любой есть единственный путь). Требуется максимизировать количество листов в получившемся дереве. Оценка линейно зависит от количества листов, при этом в тесте дано, сколько умеет жюри, и результат жюри считается за полный балл на тесте. Говорят, оптимизационная задача, в которой есть много разных подходов, по ощущениям приятнее того же канадского maze. [Wiring](http://jonathanirvin.gs/files/ioi2017/day1/wiring-ISC.p...

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IOI 2017, второй тур <center><a style="font-size:20pt;" href="http://scoreboard.ioi2017.org/Ranking.html">Таблица результатов</a></center> **SPOILER ALERT**: в комментариях и теле этого поста, скорее всего, будут обсуждаться задачи соревнования, поэтому если вы участвуете в каком-либо онлайн-зеркале, либо хотите порешать задачи самостоятельно, будьте к этому готовы. <br /> <spoiler summary="Краткий обзор задач"> Авторы соревнования, кажется, решили сделать самый оригинальный проблемсет со времён IOI 2010, и предложили во втором туре две интерактивки и одну обычную задачи. [Prize](http://ioi2017.org/tasks/day2/prize/prize-RUS.pdf). Это интерактивная задача. В ряд расположены $n \leq 200\,000$ неизвестных целых положительных чисел, причём единичка ровно одна, и если есть $x$ чисел, равных $t$, то чисел, равных $t+1$, хотя бы $x^2 + 1$. Мы можем спрашивать про позицию ряда, в ответ нам возвращается количества чисел слева и справа, меньших стоящего на выбранной позиции. Требуется за определённое кол...

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[Tuωutoωoial] Convex Polygon Counting Hi everyone, today I'm back with another blog that sadly, [user:nor,2023-10-19] won't have to spend 45 minutes GPT-ing my anime and kaomoji propaganda to read it. &#2798;&#8333; &#707; &#10521; &#706; &#8334;&#4304; &#x1f445; --- Not sure whether there is another blog explaining this technique in a "so many visualizations" manner. There are so many paper about these problems in particular. So please put your opinions and any other similar techniques you know in the comment section &#x1f4c3;&#x1f4c3;&#x1f4dc;. I think this is a "very known technique" for <span class="rated-user user-red">GM</span>s, so you guys might want to skip reading this blog. I also do expect this is a "very common geometry problem" in China or something but, here is my attempt on explaining it. Here is a cute quote by me oωo > When it comes to polygon problems, sometimes you have to see &#128038; &#127872; &#120008;&#119890;&#119892;&#120002;&#119890;&#120003;&#120009; &#127872; &#128038; in...

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Offline Dynamic MST [Tutorial] Inspired by [an old Adamant blog](https://codeforces.me/blog/entry/15296), I reinvented a variation of the technique for calculating the cost of the minimum spanning tree offline, when edge weight updates are allowed. This technique is not new and already appeared in [work of David Eppstein](https://www.ics.uci.edu/~eppstein/pubs/Epp-TR-92-04.pdf). This was also in Adamant's blog, but I missed it completely :). So the problem statement is: You're given a undirected, connected, weighted graph with $n$ nodes and $m$ edges. There are $q$ updates of the form: Set the weight of $k'th$ edge in the input to $x$. After each update you should report the total weight of a minimum spanning tree. Notice that this is strong enough to simulate edge deletions and insertions, by just giving the edge a weight of infinity when it is "deleted". This is difficult to do if you were forced to do all updates online. But offline, we can use divide and conquer on time to achieve a decent time complexity...

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Educational Codeforces Round 11 Hello, Codeforces! Educational Codeforces Round 11 will take place on [8 april 2016 at 18:00 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?msg=Educational+Codeforces+Round+11&iso=20160408T1500) for the first and the second divisions. \<The changes in the last paragraph\> 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 harder to invent interesting simple problems (like A and B) than difficult ones. So don't be afraid to suggest interesting simple or very simple tasks (of course the difficult tasks are also needed). Please send only the problems for which you know the solution with c...

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Good Bye 2015! (review, pt. 1) Hey there, I couldn't sleep, so I spend almost an hour to play with some Python and answering some questions about "who was... in 2015 on Codeforces" (also checking if I still remember anything :)). So &mdash; have you ever wondered who was the best in this year on Codeforces? I will try to answer to your (and mostly mine) questions. Here is the first part (and maybe the last :)) of this year review. [cut] In this year, there were 105 contests on Codeforces, 12 of them were not on CF rules, so there were removed from the rest of review (i,e, Educational Rounds, some ACM contests and so on). ### Most problems solved | Handle | Contests | Sum of tasks solved | Average | | :---: | :---: | :---: | :--- : | | [user:xauoyero,2015-12-31] | 52 | 112 | 2.153846 | | [user:alex_bucevschi,2015-12-31] | 53 | 106 | 2.000000 | | [user:Shavkat_Aminov,2015-12-31] | 54 | 105 | 1.944444 | | [user:ershov.stanislav,2015-12-31] | 31 | 100 | 3.225806 | | [user:Endagorion,2015-12-31] |...

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Отборочный этап Олимпиады Университета Иннополис. Второй тур. 2019-2020 **UPD: Выложены [разбор](/blog/entry/72196) и контест в тренировки [contest:102461]** Всем привет. <img src="/predownloaded/92/05/9205710589b277c79acc323594a7516232130434.png" width="500px" align="right"/> Второй отборочный тур на [Олимпиаду Университета Иннополис для школьников по информатике](https://olymp.innopolis.ru/ooui/oui-2019-20/informatics/) **перенесен** на [14 декабря в 16:00 по московскому времени](https://www.timeanddate.com/worldclock/fixedtime.html?msg=%D0%9E%D1%82%D0%B1%D0%BE%D1%80%D0%BE%D1%87%D0%BD%D1%8B%D0%B9+%D1%8D%D1%82%D0%B0%D0%BF+%D0%9E%D0%BB%D0%B8%D0%BC%D0%BF%D0%B8%D0%B0%D0%B4%D1%8B+%D0%A3%D0%BD%D0%B8%D0%B2%D0%B5%D1%80%D1%81%D0%B8%D1%82%D0%B5%D1%82%D0%B0+%D0%98%D0%BD%D0%BD%D0%BE%D0%BF%D0%BE%D0%BB%D0%B8%D1%81.+%D0%92%D1%82%D0%BE%D1%80%D0%BE%D0%B9+%D1%82%D1%83%D1%80.+2019-2020&iso=20191214T16&p1=354&ah=5). Тур длится 5 часов, в нем традиционно пять задач. Участники, показавшие высокий результат в отборочном туре, будут приглашены на заключительный эта...

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Teams qualified for ICPC Asia West Continent Championship 2024 Currently, 77 teams are selected for the ICPC Asia West Continent Championship 2024. More teams are expected to come and will update the blog as required. Comment your team's Codeforces handle and I will add them to the list. **Update:** Added columns for team ratings. Credits: [user:blitztage,2024-03-12] [Official Standings](https://wc.indiaicpc.in/?page_id=92) Asia West Region ======================== | Team Name | Institute | Member 1 | Member 2 | Member 3 | Team Rating (Max.) | Team Rating (Curr.) | |----------------- ----------|--------------------------------|----------|----------|----------|----------|----------| |SkillIssue|Indian Institute of Technology – Delhi|[user:MridulAhi,2024-03-12]|[user:ElDiablo,2024-03-12]|[user:ghoul932,2024-03-12]|2723|2612| |DunderMifflin|Indian Institute of Technology – Kharagpur|[user:Dominater069,2024-03-12]|[user:rishit3234,2024-03-12]|[user:rishabh_agarwal,2024-03-12]|2671|2509| |DU__Ascendi...

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CerealCodes Summer 2022 Programming Contest  Hello Codeforces! CerealCodes is excited to announce our Summer 2022 Programming Contest! This contest will be held on [August 13-14th](https://www.timeanddate.com/worldclock/fixedtime.html?msg=CerealCodes+Summer+2022&iso=20220813T11&p1=263) on Codeforces (with 4 different start times). The competition has three divisions: Novice (USACO Bronze-Silver or Div 3), Intermediate (USACO Silver-Gold or Div 2), and Advanced (USACO Gold-Platinum or Div 1). You can form teams of up to 3 members, and compete to solve ~6 high quality (cereal themed!) problems within 3 hours. Over $500 in cash (possibly more) will be given out (in the form of Amazon gift cards), as well as other prizes like merchandise and raffle awards!!! Note: only pre-college teams are eligible for cash awards. Join our [Discord server](https://discord.gg/qve3dBA8Ek) for more info and access to faster communication about our competiti...

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Пошаговый разбор для новичков. Codeforces Round 1101 (Div. 2) Всем Привет!  Меня зовут Максим и я очень давно хочу достичь рейтинга 3000. Я верю, что для этого мне надо научиться мыслить, как человек, у которого уже есть 3000 рейтинга. Очень часто в разборах пишут фразы "заметим, что..." или "докажем вот такой факт..." и дальше идет долгое доказательство этого факта. А то, каким образом я должен к этому факту прийти, как эта мысль должна зародиться у меня в голове, никто нигде не пишет. Я думаю, что не только у меня есть эта проблема, поэтому вместо того, чтобы ждать понятный разбор, я решил начать с себя. Именно поэтому, я решил написать свой первый пошаговый разбор, где я буду описывать ход своих мыслей и действий, которые позволяют мне придумать эти самые идеи. Также, я создал группу по прокачке навыков спортивного программирования для людей с рейтингом 1200- , чтобы помочь им стать лучше и достигнуть рейтинга 1500+. Если хотите больше об этом узнать, рекомендую пр...

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The Children Knew It All Along Everyone knows the main reason we solve these programming problems every day is because we want to solve the big question &mdash; What is the meaning of life? There is a well known book which unexpectedly answers this question with a number. That number is none other than 42. However, nobody knows what the question actually was, only the answer the computer gave. I am writing this blog to share my idea on this topic, which firstly states that 42 is just a hint to the real answer, which is, as you might have guessed, six seven. The first reason I have for this is the simple equation `42 = 6 * 7`. I believe the computer used extremely complex calculations to predict the kid saying "six seven" and thought it meant `6(7) = 42`. These calculations needed very much time and that's why it took 7.5 million years. Another reason is hidden in old Codeforces Rounds. If we look at [the person who got 67th place](https://codeforces.me/contest/43/standings/participant/48497#p48497) on [Cod...

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Пошаговый разбор для новичков. Spectral::Cup 2026 Round 2 Всем Привет!  Меня зовут Максим и я очень давно хочу достичь рейтинга 3000. Я верю, что для этого мне надо научиться мыслить, как человек, у которого уже есть 3000 рейтинга. Очень часто в разборах пишут фразы "заметим, что..." или "докажем вот такой факт..." и дальше идет долгое доказательство этого факта. А то, каким образом я должен к этому факту прийти, как эта мысль должна зародиться у меня в голове, никто нигде не пишет. Я думаю, что не только у меня есть эта проблема, поэтому вместо того, чтобы ждать понятный разбор, я решил начать с себя. Именно поэтому, я решил написать свой первый пошаговый разбор, где я буду описывать ход своих мыслей и действий, которые позволяют мне придумать эти самые идеи. Также, я создал группу по прокачке навыков спортивного программирования для людей с рейтингом 1200- , чтобы помочь им стать лучше и достигнуть рейтинга 1500+. Если хотите больше об этом узнать, рекомендую пр...

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[Tutorial] Zeta, Mobius Transform to AND, OR, GCD Convolution ## Introduction [Original Post(Korean)](https://blog.naver.com/jinhan814/223175490201) For those who have studied the Inclusion-Exclusion Principle or the Mobius Inversion formula, you may have wondered about the definition of $μ(n)$ and the process of offsetting unnecessary values by multiplying $(-1)^{|s|}$. Although it is possible to show the validity of these formulas through expansion, such proofs lack intuitive clarity. In this article, I will define Zeta and Mobius Transform on a Poset and explore examples from various Posets. Understanding these concepts will provide insights into the Inclusion-Exclusion Principle and the Mobius Inversion formula. Additionally, Zeta and Mobius Transform are essential concepts connected to SOS DP and AND, OR, GCD, LCM Convolution. In the final part of the article, we will examine interesting connections to various convolutions from Zeta and Mobius Transform. ## Table of Contents 1. What is Poset? 2. Zeta, Mobius Transform on Pose...

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Ten Years of Competitive Programming 5 Hey, Codeforces! I’m AmirReza PourAkhavan, the former Codeforces Contest Coordinator. I let the story become complete, and I’m sharing it now. The story is about a 16-year-old competitive programmer who left his family and migrated to another city alone to follow competitive programming. After seven years, he advanced to the International Collegiate Programming Contest World Finals twice. Read the previous parts: [1](https://codeforces.me/blog/entry/107465), [2](https://codeforces.me/blog/entry/108838), [3](https://codeforces.me/blog/entry/114356), [4](https://codeforces.me/blog/entry/122483). **Read the Persian version** [**here**](https://docs.google.com/document/d/1TN8pnS_8te7MLDYzMjlDxFrElNVjE4ZWjo1Ak-JJdmc/edit?tab=t.isfroku1gx3e). This part covers from December 2016 to November 2017. ## The Codeforces Contest Our contest was held on Codeforces, and it broke several records. - The record for the highest number of upvotes on an editorial. - The record f...

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Пошаговый разбор для новичков. Codeforces Round 1102 (Div. 2) Всем Привет!  Меня зовут Максим и я очень давно хочу достичь рейтинга 3000. Я верю, что для этого мне надо научиться мыслить, как человек, у которого уже есть 3000 рейтинга. Очень часто в разборах пишут фразы "заметим, что..." или "докажем вот такой факт..." и дальше идет долгое доказательство этого факта. А то, каким образом я должен к этому факту прийти, как эта мысль должна зародиться у меня в голове, никто нигде не пишет. Я думаю, что не только у меня есть эта проблема, поэтому вместо того, чтобы ждать понятный разбор, я решил начать с себя. Именно поэтому, я решил написать свой первый пошаговый разбор, где я буду описывать ход своих мыслей и действий, которые позволяют мне придумать эти самые идеи. Также, я создал группу по прокачке навыков спортивного программирования для людей с рейтингом 1200- , чтобы помочь им стать лучше и достигнуть рейтинга 1500+. Если хотите больше об этом узнать, рекомендую пр...

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Пошаговый разбор для новичков. Order Capital Round 2 (Codeforces Round 1104, Div. 1 + Div. 2) Всем Привет!  Меня зовут Максим и я очень давно хочу достичь рейтинга 3000. Я верю, что для этого мне надо научиться мыслить, как человек, у которого уже есть 3000 рейтинга. Очень часто в разборах пишут фразы "заметим, что..." или "докажем вот такой факт..." и дальше идет долгое доказательство этого факта. А то, каким образом я должен к этому факту прийти, как эта мысль должна зародиться у меня в голове, никто нигде не пишет. Я думаю, что не только у меня есть эта проблема, поэтому вместо того, чтобы ждать понятный разбор, я решил начать с себя. Именно поэтому, я решил написать пошаговый разбор, где я буду описывать ход своих мыслей и действий, которые позволяют мне придумать эти самые идеи. Также, я создал группу по прокачке навыков спортивного программирования для людей с рейтингом 1200- , чтобы помочь им стать лучше и достигнуть рейтинга 1500+. Если хотите больше об этом узнать, рекомендую прочитать [ЭТО...

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Flip-алгоритм для построения триангуляции Делоне/диаграммы Вороного за $O(n^2)$ Всем привет! Недавно я захотел сдать задачу [problem:102482G], и не смог найти нигде простую реализацию построения триангуляции Делоне. В этом блоге я хочу рассказать о том, что такое триангуляция Делоне, диаграмма Вороного, как они связаны и как их можно построить, не используя сложные структуры данных. Начнём с нескольких определений и фактов: Триангуляция &mdash; это разбиение некоторого множества точек **S** на треугольники, при этом внутренние области треугольников не пересекаются. Триангуляция Делоне &mdash; это такое разбиение некоторого множества точек **S** на треугольники, что внутри окружности каждого треугольника не находится никаких точек из множества. Диаграмма Вороного &mdash; это такое разбиение плоскости, при котором каждая область этого разбиения образует множество точек, более близких к одному из элементов множества **S**, чем к любому другому элементу множества. Диаграмма Вороного и триангуляция Делоне являются [двойственными графами](https://ru.wi...

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Пошаговый разбор для новичков. Codeforces Round 1108 (Div. 2) Всем Привет!  Меня зовут Максим и я очень давно хочу достичь рейтинга 3000. Я верю, что для этого мне надо научиться мыслить, как человек, у которого уже есть 3000 рейтинга. Очень часто в разборах пишут фразы "заметим, что..." или "докажем вот такой факт..." и дальше идет долгое доказательство этого факта. А то, каким образом я должен к этому факту прийти, как эта мысль должна зародиться у меня в голове, никто нигде не пишет. Я думаю, что не только у меня есть эта проблема, поэтому вместо того, чтобы ждать понятный разбор, я решил начать с себя. Именно поэтому, я решил написать очередной пошаговый разбор, где я буду описывать ход своих мыслей и действий, которые позволяют мне придумать эти самые идеи. Также, я создал группу по прокачке навыков спортивного программирования для людей с рейтингом 1200- , чтобы помочь им стать лучше и достигнуть рейтинга 1500+. Если хотите больше об этом узнать, рекомендую проч...

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Пошаговый разбор для новичков. Codeforces Round 1109 (Div. 3) Всем Привет!  Меня зовут Максим и я очень давно хочу достичь рейтинга 3000. Я верю, что для этого мне надо научиться мыслить, как человек, у которого уже есть 3000 рейтинга. Очень часто в разборах пишут фразы "заметим, что..." или "докажем вот такой факт..." и дальше идет долгое доказательство этого факта. А то, каким образом я должен к этому факту прийти, как эта мысль должна зародиться у меня в голове, никто нигде не пишет. Я думаю, что не только у меня есть эта проблема, поэтому вместо того, чтобы ждать понятный разбор, я решил начать с себя. Именно поэтому, я решил написать очередной пошаговый разбор, где я буду описывать ход своих мыслей и действий, которые позволяют мне придумать эти самые идеи. Также, я создал группу по прокачке навыков спортивного программирования для людей с рейтингом 1200- , чтобы помочь им стать лучше и достигнуть рейтинга 1500+. Если хотите больше об этом узнать, рекомендую проч...

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Invitation to ICM Technex 2021 — IIT (BHU) Varanasi (Rated for Div. 2 and Div. 3) Hello everyone, <br> I would like to invite you all to the International Coding Marathon 2021, under the banner of Technex'21, IIT (BHU) Varanasi. <br> Technex is the annual techno-management fest of Indian Institute of Technology (BHU), Varanasi organized from April 2-6, 2021. <br> International Coding Marathon is the flagship event of Byte The Bits, the set of programming events organized under Technex. It will take place on 6th April, 8pm &mdash; 10:30pm IST. The contest will be held on Codechef. <br> Click [here](https://www.codechef.com/ICM2021?itm_campaign=contest_listing) to go the contest page. <br> The problemset has been prepared by [user:the_nightmare,2021-04-05], [user:CoderAnshu,2021-04-05], [user:DenOMINATOR,2021-04-05], [user:rivalq,2021-04-05], [user:loud_mouth,2021-04-05], [user:_nitr0_,2021-04-05], [user:sharabhagrawal25,2021-04-05] and me, [user:shikhar7s,2021-04-05]. <br> I would like to thank [user:jtnydv25,2021-04-05], [user:Ashishgup,2021-0...

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Пошаговый разбор для новичков. Educational Codeforces Round 191 (Rated for Div. 2) Всем Привет!  Меня зовут Максим и я очень давно хочу достичь рейтинга 3000. Я верю, что для этого мне надо научиться мыслить, как человек, у которого уже есть 3000 рейтинга. Очень часто в разборах пишут фразы "заметим, что..." или "докажем вот такой факт..." и дальше идет долгое доказательство этого факта. А то, каким образом я должен к этому факту прийти, как эта мысль должна зародиться у меня в голове, никто нигде не пишет. Я думаю, что не только у меня есть эта проблема, поэтому вместо того, чтобы ждать понятный разбор, я решил начать с себя. Именно поэтому, я решил написать пошаговый разбор, где я буду описывать ход своих мыслей и действий, которые позволяют мне придумать эти самые идеи. Также, я создал группу по прокачке навыков спортивного программирования для людей с рейтингом 1200- , чтобы помочь им стать лучше и достигнуть рейтинга 1500+. Если хотите больше об этом узнать, рекомендую прочитать [ЭТО...

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UTPC Fall 2024 Contest #1 Hello, Codeforces! [UTPC](https://www.cs.utexas.edu/users/utpc/index.html), the competitive programming organization at the University of Texas at Austin, is happy to invite you to participate in the first contest of the UTPC Fall contest season which will be held on [Friday, September 13, 2024 at 6:00PM UTC-5 (CDT)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=UTPC+Fall+2024+Contest+%231&iso=20240913T18&p1=24&ah=2). You will be given 8 problems (roughly ordered by difficulty) and 2 hours to solve them, with standard ICPC scoring. There will be a wide range of difficulties -- anyone is welcome to participate! We have will two divisions, Div. 2 for beginners to competitive programming and Div. 1 for people with some experience. This is a **team** contest, meaning that you are allowed to compete in teams of up to 3 members (it is totally acceptable to compete without teammates as well). This is (of course) not an official Codeforces round, and is thus unrated. The p...

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Educational Codeforces Round 112 [Rated for Div. 2] Hello Codeforces! On [contest_time:1555] [contest:1555] will start. Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.me/blog/entry/51208">blog post</a>. 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 will have access to copy any solution and test it locally. You will be given **6 or 7 problems** and **2 hours** to solve them. The problems were invented and prepared by Adilbek [user:adedalic,2021-07-29] Dalabaev, Vladimir [user:vovuh,2021-07-29] Petrov, Ivan [user:BledDest,2021-07-29] Androsov, Mak...

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Learning Notes on the Hopcroft-Tarjan planarity algorithm (With C++ Implementation) **Section 1. Introduction** I have been struggling for weeks to understand the first linear-time planarity algorithm, the [Hopcroft-Tarjan algorithm (HT)](https://www.cs.princeton.edu/courses/archive/fall05/cos528/handouts/Efficient%20Planarity.pdf). Fortunately, I successfully understood it and implemented it. In fact it is very hard to find a verified HT implementation online. Some code, e.g., [LEDA](https://en.wikipedia.org/wiki/Library_of_Efficient_Data_types_and_Algorithms) is not open source. Other open-source planarity tests, e.g., [networkx (LR planarity)](https://github.com/networkx/networkx/blob/main/networkx/algorithms/planarity.py), [boost (Boyer-Myrvold)](https://www.boost.org/doc/libs/1_53_0/libs/graph/doc/boyer_myrvold.html), [Pigale (LR planarity)](https://pigale.sourceforge.net/), use other algorithms. There is [an implementation by Shawn Anderson](https://github.com/shawnwanderson/Hopcroft-Tarjan-Planarity-Testing), however it is partial. I would like to open a blo...

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Invitation to ICM Technex 2019 — IIT(BHU) Varanasi I would like to invite you all to the **International Coding Marathon 2019**, under the banner of Technex'19, IIT (BHU) Varanasi. [Technex](https://www.technex.in/) is the annual techno-management fest of Indian Institute of Technology (BHU), Varanasi organized from March 8 &mdash; 10, 2019. International Coding Marathon is the flagship event of [Byte The Bits](https://www.technex.in/events/), the set of programming events organized under Technex. ICM is brought to you by [Mentor Graphics](https://www.mentor.com/india). It will take place on [Friday, 8th March 2019, 21:00 IST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=ICM+Technex+2019+by+IIT+%28BHU%29&iso=20190308T1530&ah=2). The contest will be held on [Codechef](https://www.codechef.com/ICMT2019?utm_source=contest_listing&utm_medium=link&utm_campaign=ICMT2019). The problemset has been prepared by [user:hitman623,2019-03-06], [user:dhirajfx3,2019-03-06], [user:_shanky,2019-03-06], [user:drastogi21,2019-03-08...

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Codeforces Beta Round #92 - Analysis <div align="center"><b>Div-2. [[problem:124A]]</b><br /><div align="left">Let's iterate through the each item and check whether it is appropriate to the conditions $a \le i-1$ and $n - i \le b$ (for $i$ from $1$ to $n$). The first condition can be converted into $ a +1\le i$, and the condition $n - i \le b$ in $ n - b \le i$, then the general condition can be written $ max (a +1, n-b) \le i$ and then our answer can be calculated by the formula $ n-max (a +1, n-b) +1 $.<br />[[submission:835581,The author's solution]]<br /></div></div><div align="center"><b><br />Div-2. [[problem:124B]]</b><br /><div align="left">Let's try all possible ways to rearrange digits in the numbers and check the difference between maximum and minimum number.<br />[[submission:835584,The author's solution]]<br /></div></div><div align="center"><b><br />Div-1. [[problem:123A]]<br />Div-2. [[problem:124C]]</b><br /><div align="left">All positions except the first and those whose number is a prime greater $|s| / 2...

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ALL CodeForces Rounds Tutorial <html> <body> <br /><br /> >>>>>>>**Hi I just Say Really Sorry For Delay in UPD This Blog...!**<br /><br /><br /> <u>This is not Complete</u> , but i try to find <b>all Tutorial codeforces round</b> and posted here , thanks in advance :D <br /><br />This post will <b> <span class="Apple-style-span" style="border-collapse: collapse;color: rgb(255,0,0);font-family: verdana , arial , sans-serif;font-size: 12.0px;"> UPD</span></span></b> after each contest . <span>If anyone have or writes any editorial that's</span> <b> <span> <span class="Apple-style-span" style="border-collapse: collapse;color: rgb(255,0,0);font-family: verdana , arial , sans-serif;font-size: 12.0px;"> not in here</span></span></b> , Plz post here for ALL . <br /><br /><b>UPD </b> &nbsp;: Table1 updated : in Future!!! <br /><br /><b>UPD </b>&nbsp;: Table2 updated : CF # 118 ...to... CF # 169 added .<br /><br /> </p><hr /><br /></p> <div align="justify"> <br /><br /><b><s...

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Formula VS binary search (precision issue on AtCoder) Recently I was upsolving [this problem](https://atcoder.jp/contests/abc356/tasks/abc356_g). My subtask was as follows: given three points: `A, B, C`, and I need to find the intersection point of 2 lines: AB and OC, where O has (0;0) coordinates. <spoiler summary="Code, 90/92 tests passed"> ~~~~~ #include <bits/stdc++.h> using namespace std; #define ll long long #define ld long double #define fi first #define se second #define pb push_back #pragma GCC optimize("unroll-loops,O3") #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt") #define cok cout << (ok ? "YES\n" : "NO\n"); #define dbg(x) cout << (#x) << ": " << x << endl; #define dbga(x,l,r) cout << (#x) << ": "; for (int ii=l;ii<r;ii++) cout << x[ii] << " "; cout << endl; #define int long long #define pi pair<int, int> const int N = 1e6+9; int n, q; struct pt { int x, y; pt operator-(pt b) {return {x - b.x, y - b.y};} int operator%(pt b) {return x * b.y - y * b.x;} int len() {return x * x + y *...

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Sorted list of IOI participants by codeforces max rating 1.  [user:matthew99,2017-06-09] 3100 2.  [user:Reyna,2017-06-09] 2771 3.  [user:geniucos,2017-06-09] 2762 4.  [user:yutaka1999,2017-06-09] 2704 5.  [user:jiaqiyang,2017-06-09] 2671 6.  [user:arsijo,2017-06-09] 2638 7.  [user:Enchom,2017-06-09] 2630 8.  [user:Narenji58,2017-06-09] 2613 9.  [user:kefaa,2017-06-09] 2606 10.  [user:pacu,2017-06-09] 2594 11. ![ ]...

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NITS Hacks 6.0 Inter College Coding Competition (Prizes worth 50k INR) Calling all coders! Get ready for the thrilling Competitive Programming Contest of **[NITS HACKS 6.0](https://nitshacks.tecnoesis.co.in/)** in association with **Coding Club NIT Silchar**, under the event **[Tecnoesis](https://www.tecnoesis.co.in/)**, of NIT Silchar. The thrill and fun of team contest is back, with exciting prizes! The coding competition is open to all undergraduate programmers in India, although everyone is encouraged to participate in it. It will be split into preliminary and final rounds according to **ICPC guidelines** (both rounds will be online). The final round awaits the top 30 preliminary teams out of which 10 spots are reserved for NIT Silchar Teams (excluding the top 20). **Rules:** - A team of 2-3 members from the same college is required to participate in the contest. - An eligible individual may join only one team. - Each participant must have a Codeforces account. - A team must be created in Codeforces composed of the members. ...

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Codeforces Round #840 (Div. 2) and Enigma 2022 — Cybros LNMIIT Editorial We hope you liked the problems! Unfortunately, problem C turned out to be harder than usual. Please read its editorial, we hope you'll find that the intended solution is not that hard. # [problem:1763A] Idea: [user:DreadArceus,2022-12-19]<br> Prepared by: [user:DreadArceus,2022-12-19] <spoiler summary="Hint 1"> Which $1$s in the binary representation cannot be changed to $0$. </spoiler> <spoiler summary="Hint 2"> Similarly, Which $0$s in the binary representation cannot be changed to $1$. </spoiler> <spoiler summary="Need more hints?"> Considering the last two hints, try to maximize the maximum element and minimize the minimum element. </spoiler> <spoiler summary="Solution"> In the minimum element, we want to make every bit $0$ when possible, it won't be possible to set a particular bit to $0$ when that bit is set in all the elements of $a$. Therefore, the minimum value we can achieve after performing the operations is the bitwise AND of all the elements of $a$...

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Yandex.Algorithm 2020 D — my solution UPD: 10 points! Ha! <spoiler summary="implementatio programmi"> ~~~~~ string S; cin >> S; int L = S.length(); vector<tok> A; for(int i = 0; i < L; i++) if(S[i] != '0') { int z = 0; for(int j = i+1; j <= L; j++) { if(j == L || S[j] != '0') break; z++; } A.push_back({.lead = S[i]-'0', .num_0 = z}); } string ans2[10][10]; for(int d1 = 1; d1 < 10; d1++) for(int d2 = 0; d2 < 10; d2++) { ans2[d1][d2] += ('0'+d1); cat pw = 1; for(int i = 0; i < d2; i++) pw *= d1; if(pw > 10*d1+d2) ans2[d1][d2] += "**"; ans2[d1][d2] += ('0'+d2); } string ans3[10][10][10]; string ans4[10][2][10][10]; for(int d1 = 1; d1 < 10; d1++) for(int d2 = 0; d2 < 10; d2++) for(int d3 = 0; d3 < 10; d3++) { ans3[d1][d2][d3] += ('0'+d1); dbl lpw0 = log(100*d1+10*d2+d3); dbl lpw1 = d2 ? (10*d2+d3)*log(d1) : 0; dbl lpw2 = d3*log(10*d1+d2); dbl lpw3 = 0; if(d2 && d3) { lpw3 = log(d1); for(int i = 0; i < d3; i++) lpw3 *= d2; } dbl lmax = max(max(lpw0, lpw1), max(lp...

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tgen::miniblog(6): random non-collinear points <center> <img src="/predownloaded/72/82/7282f22a0748c711b1964af0315893578b0d32d5.png" style="width: 350.0px;max-width: 100.0%;max-height: 100.0%;"> </center> <i>This is blog 6 of a series of blogs about algorithmic challenges I came across when creating [tgen](https://codeforces.me/blog/entry/154468).</i> In this blog we will tackle: 1. Generate $n$ random distinct integer points in an $O(n) \times O(n)$ box, with no three collinear, in $\mathcal O(n)$ time. We call such set of points (all distinct, with no three collinear) to be in **general position**. This is useful when testing geometry problems. Our construction has no uniformity guarantee: we do not sample uniformly from all general-position point sets in the box. Our goal is only for the points to *look* random, in the sense that they have no obvious geometric pattern. Picking random grid points and rejecting a point whenever it forms a line with two previous points is expensive: there are already $\Theta(k^2)$ fo...

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XVII Всероссийская командная олимпиада школьников по программированию <img src="http://codeforces.me/predownloaded/77/bc/77bc362569784338b604c16320795087a30c12f0.jpg" align="right" style="height: 400px; margin: 10px;" alt="text"/> [Окончательные результаты](http://neerc.ifmo.ru/school/archive/2016-2017/ru-olymp-team-russia-2016-standings.html) [Запись видеотрансляции соревнования](https://www.youtube.com/watch?v=1PzAr2IUDM4) [Запись разбора задач и церемонии награждения](https://www.youtube.com/watch?v=2nd-9rbjSCE) [Зеркало на сайте Яндекс.Контест](https://contest.yandex.ru/contest/3576/enter/) Всем привет. В эти выходные в стенах Университета ИТМО в Санкт-Петербурге, а также в Барнауле, Ташкенте, Алматы и Тбилиси пройдет семнадцатая всероссийская командная олимпиада школьников по программированию. В этом ВКОШП участвуют [больше 230 команд](http://neerc.ifmo.ru/school/russia-team/listTeamsFinal.jsp) из них 101 команда в Санкт-Петербурге. Тур начнется в воскресенье 11 декабря 2016 года в [10:00](http://www.timeanddate.com/worldcl...

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Республиканская юниорская олимпиада 2021 года. Казахстан. Результаты. ### 7 класс <table> <thead> <tr> <th>Место</th> <th>ФИО</th> <th>CF handle</th> <th>Балл</th> <th>Медаль</th> </tr> </thead> <tr> <td>1 </td><td>Серазитдинов Назар</td><td>[user:Meshok_adventure,2021-05-21]</td><td>157</td></td><td><img alt=" " src="/predownloaded/93/73/9373156f429b185ba6bc779f81d16894f9a72d9e.png" style="max-width: 100.0%;max-height: 100.0%;"></td> </tr> <tr> <td>2 </td><td>Ли Арсен</td><td>[user:AtLeeast,2021-05-21]</td><td>145</td></td><td><img alt=" " src="/predownloaded/93/73/9373156f429b185ba6bc779f81d16894f9a72d9e.png" style="max-width: 100.0%;max-height: 100.0%;"></td> </tr> <tr> <td>3 </td><td>Нургалиев Альжан</td><td></td><td>137</td></td><td><img alt=" " src="/predownloaded/93/73/9373156f429b185ba6bc779f81d16894f9a72d9e.png" style="max-width: 100.0%;max-height: 100.0%;"></td> </tr> <tr> <td>4 </td><td>Асланов Амир</td><td>[user:Pragmatist2.0,2021-05-21]</td><td>135</td></td><td><img alt=" " sr...

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Schroeppel and Shamir's algorithm for subset sum or a cool idea to divide in 4 Hello, codeforces! Today I decided to write my first English blog on codeforces and present an interesting optimization for the subset sum problem. I found out about this technique in my high school and decided to explain it properly in the blog on codeforces. ##Problem statement Given an array $a$ of size $n$ and an integer $C$. Find a subset with distinct indices $\lbrace i_1, i_2, ..., i_k\rbrace$ so that $\sum_{j = 1}^{k} a_{i_j} = C$. ##Simple solution We can use here a meet-in-the-middle technique by dividing an array in 2 equal parts, putting all subset sums from first half in any structure like hash map, iterating through subsets in second half, calculating their $sum$ and trying to find $C - sum$ in our structure. This solution requires $O(n \cdot 2^{n/2})$ time and $O(2^{n/2})$ space if we greedily calculate sum of every subset with a loop. This can be improved down to $O(2^{n/2})$ time complexity if we find all our sums in another way: let's initialize a...

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XV Всероссийская командная олимпиада школьников по программированию <html> <body> Всем привет! На этих выходных состоится [Пятнадцатая ВКОШП](http://neerc.ifmo.ru/school/russia-team/index.html). [232 команды](http://neerc.ifmo.ru/school/russia-team/listTeamsFinal.jsp) будут соревноваться на семи площадках: в Санкт-Петербурге, Барнауле, Алматы, Ташкенте, Тбилиси, Кременчуге и Ереване. Пресс-служба NEERC в полном составе обитает на площадке в Санкт-Петербурге в университете ИТМО, где сегодня началась интенсивная подготовка к проведению соревнования. Около 80 волонтеров и работников техкомитета на момент написания этого поста собирают шесть холлов, где будет в эти выходные находиться 101 команда, проверяют сетевое подключение и тестирующую систему, и еще много всего для того, чтобы соревнование прошло без проблем. В субботу у нас состоится регистрация, открытие и пробный тур, а в [10:00 по московскому времени](http://www.timeanddate.com/worldclock/fixedtime.html?msg=%D0%92%D0%9A%D0%9E%D0%A8%D0%9F%202014&iso=20141130T1000) в воскресенье 30 ноября...

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Сентябрь 2016: Мини-сборы по программированию в Ростове и Самаре В сентябре пройдут мини-сборы по программированию в двух региональных вузах &mdash; ЮФУ в Ростове (19-24 сентября) и СГАУ в Самаре (26 сентября-1 октября) &mdash; подготовка к четвертьфиналу ACM-ICPC, который [пройдет в октябре в Саратовском ГУ](https://contest.sgu.ru/). Подобное мероприятие проводится впервые &mdash; это инициатива фонда [Botan Investments](http://botaninvestments.com/) с целью помочь развитию программирования в региональных вузах. Артем [user:VArtem,2016-09-14] Васильев и Николай [user:Niko,2016-09-14] Ведерников &mdash; аспиранты и преподаватели ИТМО, организаторы сборов по программированию в России и за рубежом, члены жюри олимпиад по информатике для школьников и студентов, авторы задач по программированию. Недавно они выступили организаторами [Международной олимпиады по информатике IOI 2016](http://codeforces.me/blog/entry/46717) в составе научного и технического комитета. Артем Васильев &mdash; победитель финала ACM-ICPC 2015 (Марракеш, Марокко), победитель...

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CF Custom Contests: Learn & Climb Faster (Chrome Extension) **UPD:** Thank you all for 300+ downloads in just a week! I've shipped an update with new features like analytics. Details are in [this post](https://codeforces.me/blog/entry/142919)! **TLDR:** Create custom contests instantly to efficiently train! Download on the [Chrome Web Store](https://chromewebstore.google.com/detail/codeforces-custom-contest/iafalaippdkpmfpicnhoccfbbkgnelpg?authuser=0&hl=en) Train Specific Skills & Improve Rating ================== Frustrated when problems in virtual contests jump from doable to impossible? Want to train speed or problem solving specifically? The **CF Custom Contests** extension makes this effortless! Key Features ------------------ This extension elevates your training experience by providing the following features - **Contest Settings:** Choose **problem count** & **ratings** and **contest length**. Short contest + easier problems for speed drills OR longer contest + harder problems for problem solving practice - **Contest:**...

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Surprise Language Round #8 Язык этого раунда &mdash; **Kotlin**. Kotlin (Ко́тлин) — статически типизированный язык программирования, работающий поверх JVM и разрабатываемый компанией JetBrains. Вот вам пример простейшей программы, которая выводит сумму двух чисел: ~~~~~ fun main(args: Array<String>) { val (x, y) = readLine()!!.split(' ').map(String::toInt) println(x + y) } ~~~~~ Для того, чтобы познакомиться с языком мы предлагаем вам почитать следующие материалы: * [https://en.wikipedia.org/wiki/Kotlin_(programming_language)](https://goo.gl/gYZ5xD) * https://kotlinlang.org/docs/reference/ * http://try.kotlinlang.org/ &mdash; осторожно, чтение с консоли во web-IDE не разрешено * [введение в Kotlin на русском](https://vk.com/pages?oid=-59097513&p=%D0%92%D0%B2%D0%B5%D0%B4%D0%B5%D0%BD%D0%B8%D0%B5_%D0%B2_%D1%8F%D0%B7%D1%8B%D0%BA_Kotlin) * и Google к вам в помощь! Вы можете отдельно выкачать компилятор языка версии 1.0.1 по ссылке http://s.codeforces.com/files/kotlin-compiler-1.0.1.zi...

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Div.1 Round Registrants & Participants Consider the following Div. 1 rounds:<br/><br/> [contest:403]<br/> [contest:406]<br/> [contest:407]<br/> <pre> Registrants Participants #236: 1011 616 (61%) #238: 1052 608 (58%) #239: 774 538 (70%) </pre> At least, **30%** of registered users didn't participate in the rounds.<br/> Do you wonder, what they really do? Do they read the problem statements or not?<br/><br/> [cut] <br/> #### Intro It was interesting for me, and I've analyzed the following information:<br/> - round registrants list <br/> - last visit time of each round registrant during round (polling interval was **5 minutes**)<br/> - official participants list <br/> In other words, ~1000 http-requests were made each 5 minutes.<br/> Dear Codeforces, I beg your pardon, if it was to much :) <br/> **I don't plan to acquire this kind of statistics anymore**.<br/> #### Brief results <pre> round userColor registrants participants neverVisited silentlyVi...

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Built a website that forces you to practice what you're actually bad at, not what's comfortable Hey guys, I want to share something I've been building. I'm a 2nd year student, and I practice on Codeforces, LeetCode, and CodeChef. For a while I kept running into the same annoying problem — my progress was scattered across three tabs, three different rating systems, three different "weak topics," and I had no single place to actually see how I was doing or what I should practice next. So over the past few months I built CPPro to fix that for myself, and figured some of you might find it useful too. **What it actually does** It's a single platform that pulls your CF + LC + CodeChef data together — ratings, heatmap, contest history, topic-wise solve counts. Nothing groundbreaking on its own, I know there are tools that already do parts of this. The part that's actually different from most trackers is the daily problem system. Instead of generic "problem of the day" picks, it looks at your actual solve history across all three platforms and gives you two problems every ...

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C++11. Все, что нужно олимпиаднику. Всем привет! В качестве предисловия отмечу, что эта статейка написана скорее от нечего делать, нежели ради благих целей, но тем не менее, надеюсь, что некоторую пользу она все же принесет. Заниматься олимпиадами я больше не хочу, поэтому это что-то вроде "прощания" с миром спортивного программирования. Звучит глупо, но начать как-то надо было... Как известно, на данный момент официальным стандартом С++ является ISO/IEC 14882:2011, или же, проще говоря, С++11. Поддерживается он не на всех серверах, но со временем, думаю, ситуация изменится. Codeforces, например, идет в ногу со временем. C++0x, доступный здесь, фактически ничем от С++11 не отличается, просто другое наименование ("рабочее" название в ходе работы над будущим стандартом на самом деле). По крайней мере, начиная с GCC 4.7, установленного здесь, это так. Сразу скажу, что я буду опираться на GCC, ибо в Visual C++ практически все новые фичи появляются только в 10 и, в основном, 11 версии, которые не шибко то распространены....

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Результаты Республиканской Олимпиады по Информатике 2024 Это результаты республиканской олимпиады по информатике 2024 ([user:Kazakhstan,2024-02-20]) <spoiler summary="Результаты прошлых лет"> [2023](https://codeforces.me/blog/entry/114266) [2022](https://codeforces.me/blog/entry/102044) [2021](https://codeforces.me/blog/entry/90111) [2020](https://codeforces.me/blog/entry/80808) [2019](https://scoreboard.bc-pf.org/results/informatics/national-olympiad/2019) [2018](https://scoreboard.bc-pf.org/results/informatics/national-olympiad/2018) [2017](https://scoreboard.bc-pf.org/results/informatics/national-olympiad/2017) </spoiler> 9 класс ----------- <table> <thead> <tr> <th>Место</th> <th>ФИО</th> <th>CF handle</th> <th>1 тур</th> <th>2 тур</th> <th>общий</th> <th>Медаль</th> </tr> </thead> <tr> <td> 1 </td> <td> Мамадахунов Мансур </td> <td> [user:Wansur,2024-03-26] </td> <td> 282.07 </td> <td> 181 </td> <td> 463.07 </td> <td> <img alt=" " src="/predownloaded/93/73/9373156f429b185ba6bc779f81d16894f9a7...

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Реализация встречного дерева Фенвика для RMQ или ДО для курильщиков Доброго времени суток! Началось все с того, что после прочтения [статьи](https://neerc.ifmo.ru/wiki/index.php?title=%D0%92%D1%81%D1%82%D1%80%D0%B5%D1%87%D0%BD%D0%BE%D0%B5_%D0%B4%D0%B5%D1%80%D0%B5%D0%B2%D0%BE_%D0%A4%D0%B5%D0%BD%D0%B2%D0%B8%D0%BA%D0%B0) про встречное дерево Фенвика, я начал искать в интернете его реализацию, но (спойлер) так и не нашел. Безусловно, тема не нова, но, к сожалению, статью, описывающую эту структуру данных с приведенными примерами реализации, я так и не нашел. Перед прочтением данного поста советую ознакомиться с указанной статьей, т.к. на нее будут опираться все дальнейшие рассуждения. Встречное дерево Фенвика ================== Для начала, вспомним определение: Встречное дерево Фенвика (англ. counter tree Fenwick) — дерево Фенвика, в котором над каждым столбцом идет столбец такой же высоты, вычисляемый по формуле $f_{rev}[i]=\sum\limits_{j=i+1}^{i+2^{h(i)}}a[j]$. Сразу сделаю уточнение, что под прямым деревом Фенвика подразумевается массив, посчита...

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What happened to 1400+ Codeforces users from 2021 to now? I took every Codeforces user who (a) was rated **1400 or higher at some point in 2021** and (b) is **still competing** (active rated list, and at least one rated contest since 2025-01-01). That is **746 users**. I pulled their full rating histories from the public Codeforces API and measured the cohort at each major AI release that mattered for competitive programming. All numbers below come from `user.ratedList` and `user.rating`. Data was fetched on 2026-10-08. Charts and code are available on request. **Important caveat up front:** this post shows *what happened*. It does not show *why*. Rating trends have many causes, and I mark clearly where I'm speculating. ## How the cohort was built 1. `user.ratedList?activeOnly=true` returned 43,131 active rated users. 2. I kept those registered by the end of 2021 whose max rating is ≥ 1400: **1,600** candidates. 3. For each candidate I fetched `user.rating` and kept those whose rating was ≥ 1400 at any time in 2021 (including th...

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Who participated most in 2019? This is top users with most participated in official contests of 2019, included non-rated ones. |Rank|Handle|Total|Official|Unofficial| |---|---|---|---|---| |1|[user:Mukundan314,2019-12-27]|104|103|1| |2|[user:titia,2019-12-27]|103|82|21| |3|[user:risujiroh,2019-12-27]|103|63|40| |4|[user:mini4141,2019-12-27]|102|95|7| |5|[user:Black_Ghost,2019-12-27]|102|85|17| |6|[user:ruban,2019-12-27]|99|90|9| |7|[user:kmjp,2019-12-27]|98|55|43| |8|[user:youx,2019-12-27]|97|82|15| |9|[user:spookywooky,2019-12-27]|97|93|4| |10|[user:raj1307,2019-12-27]|97|97|0| |11|[user:k24,2019-12-27]|97|85|12| |12|[user:Noob-ita-pro,2019-12-27]|97|97|0| |13|[user:spellstaker,2019-12-27]|96|90|6| |14|[user:shahidul_brur,2019-12-27]|96|89|7| |15|[user:bhatnagar.mradul,2019-12-27]|96|84|12| |16|[user:Def4ULt,2019-12-27]|96|95|1| |17|[user:naeeem,2019-12-27]|95|95|0| |18|[user:leaf1415,2019-12-27]|95|54|41| |19|[user:kzyKT,2019-12-27]|95|71|24| |20|[user:eugalt,2019-12-27]|95|95|0| |21|[user...

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Альфа-банк поддержал олимпиадников-первокурсников <img src="http://codeforces.me/predownloaded/92/dc/92dcd8c9a59bc414b6cf0bad8607fabc8942b726.png" style="float:right; margin: 0 1em 1em 1em;"> Объявлены лауреаты программы «Альфа-Шанс» 2016 года, которые в течение двух лет будут получать ежемесячно от 5 до 10 тысяч рублей в зависимости от вуза. Претендовать на стипендию [«Альфа-Шанс»](https://alfabank.ru/about/society/alfa-chance/) могут студенты первого курса из регионов России (кроме Москвы), являющиеся победителями или призерами заключительного этапа Всероссийской олимпиады школьников и победителями (Диплом 1 степени) межрегиональной олимпиады школьников НИУ ВШЭ «Высшая проба». [Конкурсный отбор](https://alfabank.ru/about/society/alfa-chance/competition/) проводится [ежегодно](https://alfabank.ru/about/society/alfa-chance/scholars/) на основании анкет участников, эссе и очного собеседования. В этом году в качестве темы эссе была выбрана тема «Не расставайтесь со своими иллюзиями. Когда их не станет, может быть вы и продолжи...

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Divide by Zero 4.0 Summary ##Statistics Total Users/Teams who have made a submission: **754** Total Submissions: **4212** Number of distinct users/teams with correct submissions: **498** [Contest Link]( https://www.codechef.com/DIBZ2016) [Feedback form](http://goo.gl/forms/cMY4KZLEJV) --- ##Winners <li>Rank 1: [user:Sumeet.Varma,2016-01-31]</li> <li>Rank 2: [user:amankedia1994,2016-01-31]</li> <li>Rank 3: [user:PrashantM,2016-01-31]</li> --- The Editorials of the following problems are prepared by me, [user:aditya1495,2016-01-31] and [user:_shil,2016-01-31]. --- ##Shil and RasenShuriken (setter: [user:_shil,2016-01-31])<br> Total number of pairs such that their product is even. Count total number of odd numbers = x.<br> Product of two numbers is odd if the both numbers are odd.<br> Ans = **N*(N-1)/2 &mdash; x*(x-1)/2** --- ##Shil Loves Exclusive Or (setter: [user:_shil,2016-01-31])<br> Use the fact that Xor of 2x and 2x+1 is 1.<br> Therefore xo...

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Codeforces Beta Round #92 <p>&quot;Tryam&quot; to everyone!<br /><br />I am an authors of the today's contest. First of all I want to thank <b>Artem Rakhov</b> [[[user:RAD,2011-11-03]]] (thanks to him, you'll understand my problems) and <b>Maria Belova</b> [[[user:Delinur,2011-11-03]]] (those who know my English level will understand a huge of my thanks). Also thanks to everyone staff for the wonderful of the codeforces system. And also thanks to <b>Sergei Tarasov</b> [[[user:Seryi,2011-11-03]]] and <b>Andrey Tkachenko</b> [[[user:TBGame,2011-11-03]]] for ideas generating and testing.<br /><br />Good luck and have fun.</p> <p><span lang="en"><span class="hps">Today,</span> <span class="hps">a breakdown of</span> </span>score <span lang="en"><span class="hps">will be slightly different</span> <span class="hps">from the standard</span> <span class="hps">-</span> <span class="hps">for</span> <span class="hps">the second division</span> <span class="hps">is <b>500-1000-2000-2000-2500</b></span> <span class="hps"...

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CF Heroes: Space Всем привет, мы студенты Самарского университета, решили анонсировать свою новую игру. В прошлом году мы успешно запустили игру CF Heroes, которая стала абсолютным бестселлером и обрела кучу поклонников. Мы опросили тысячи людей, исследовали их мнения и решили разработать новую игру, кардинально изменив концепцию. Теперь мы отправляем наших Героев в ... космос! 2025 год. В солнечную систему вошел неизвестный объект. Он стремительно направился к Земле. Решением ООН на осмотр был отправлен автоматический зонд. Подойдя к похожему на астероид объекту, названному "Дельта-0", на несколько десятков тысяч километров, зонд практически испарился. В ответ на это с Земли был произведен массовый ракетный отстрел и десятки ядерных боеголовок уже через несколько часов они прожгли насквозь тяжелый крейсер неизвестных инопланетян. В ООН сразу же пошло массовое обсуждение данного вопроса. Каждая из стран предлагала разные решения для данной проблемы: РФ предложила разместить на орбите как можно...

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Special Prize for “Goodbye 2018” Round  <br> <br> **Hello, Codeforces!** Happy Holidays from us at Harbour.Space University, and good luck on the [contest:1091] round This year’s Final Round has a special prize &mdash; as you might know, we’ve prepared a new installment to the “Hello! Programming Bootcamps”...this time, our destination is the pearl of the Middle East — **Muscat**, Oman. So, **as a special prize for this Final Codeforces Round**, the **top 3 participants**, who are also eligible for ICPC 2019/2020 season, will be **invited to form a team and join us in Oman for the [2019 “Hello Muscat!” Programming Bootcamp](https://in.harbour.space/icpc/icpc-hello-muscat-bootcamp-2019/?utm_source=codeforces)** in 9 — 15 of March — sponsored with their participation fees, accommodation, and meals for the entire duration of the bootcamp (except flights)! Registering to the the round you will be asked to confirm your eligibility for ICPC 20...

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XXIII Командный чемпионат школьников Санкт-Петербурга по программированию <html> <body> <img src="http://codeforces.me/predownloaded/bf/64/bf642a972f05376ef9709036a1ff0f29a6d5c705.jpg" align="right" style="height: 280px; margin: 20px;" alt="text"/> В середине декабря пройдет XVI Всероссийская командная олимпиада школьников по программированию. Некоторые отборочные региональные соревнования уже прошли, и результаты уже подведены: - [Екатеринбург](http://acm.timus.ru/monitor.aspx?id=303)<br> - [Саратов](http://contest.sgu.ru/monitor/3)<br> - [Рыбинск](http://www.rgata.ru/arch/acm_info_2015_6.pdf)<br> - [Минск](http://www.oi-minsk.id1945.com/city-acm/results1017.pdf) <br> В воскресенье 25 октября 2015 года в Санкт-Петербурге в Университете ИТМО состоится Командный чемпионат школьников СПб по программированию. В соревновании будут участвовать более [90 команд](http://neerc.ifmo.ru/school/spb/listTeams.jsp). Информацию и расписание соревнований можно найти [здесь](http://neerc.ifmo.ru/school/spb/index.html). Кроме того, на [сайте](http://neerc...

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Hack me! (Codeforces Round #277.5 (Div. 2)) Welcome after the long break in Hack me! ([contest:489]). Previous posts can be found [here](http://codeforces.me/search?query=hackme). [cut] <h3>Stats</h3> Problem | <small>Successful hacks</small> | <small>Unsuccessful hacks</small> | Other* | Sum | <small>Solutions which can be hacked</small> | <small>Accepted solutions</small> | <small> All solutions on final tests</small>| :---:|:---:|:---:|:---:|:---:|:---:| <small> [problem:489A] </small> | 11 (28.21%) | 24 (61.54%)| 4 (10.26%) | 39 | 400 (17.22%) | 1923 (82.78%) | 2323 | <small> [problem:489B] </small> | 185 (61.26%) | 102 (33.77%)| 15 (4.97%) | 302 | 427 (18.09%) | 1934 (81.91%) | 2361 | <small> [problem:489C] </small> | 8 (11.59%) | 59 (85.51%)| 2 (2.90%) | 69 | 158 (8.90%) | 1618 (91.10%) | 1776 | <small> [problem:489D] </small> | 2 (14.29%) | 6 (42.86%)| 6 (42.86%) | 14 | 38 (4.99%) | 724 (95.01%) | 762 | <small> [problem:489E] </small> | 0 | 0 | 0 | 0 | 23 (41.07%) | 33 (58.93%)| 56 | <small> [problem:4...

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Anti-hash test. Hi everyone! I wan't to share some interesting fact about how we're going to challenge almost every solution, that uses polynomial hashes modulo 2^64. We'll hack any solution, regardless of it's base (!), the only thing we need, that it's using int64 with overflows --- like many coders write hashing. Keywords: Only today, only for you, ladies and gentlemen: we're gonna challenge [user:Petr,2012-07-19]'s solution in problem [problem:7D] from Codeforces Beta Round #7! Is it interesting? Welcome reading after the cut. [cut] Firstly, for the most impatient of you. Here's the source of the generator: ~~~~~ const int Q = 11; const int N = 1 << Q; char S[N]; for (int i = 0; i < N; i++) S[i] = 'A' + __builtin_popcount(i) % 2; // this function in g++ returns // number of ones in binary representation of number i ~~~~~ Let's try solutions of two CFBR #7 winners on this test: Petr Mitrichev's and Vlad Epifanov's. [user:vepifanov,2012-07-18] solution doe...

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Breakthrough in 1955G — Bitset where you least expect Two days ago, the Div.3 ([contest:1955]) suffered from severe issues of hacks, because the problem G ([problem:1955G]) did not have proper validation for the sum of $nm$ in hacks, which was specified as at most $2 \cdot 10^5$ in the statements. Sure, I won't ask about why that happened, that is not constructive discussion. Instead, I will discuss about something very interesting about the task. During that incident, I was wondering. There has to be a way to solve this without the constraint on $n \cdot m$, right? Of course, $7\times 10^8$ bytes of input is impossible anyways, but if we ignore that, $10^8$ is not a very "dreaded" number under these ages of optimizations. There has to be a way to do this. Then the idea came to me. ------ Before we cover the solution, we cover a few basic facts on number theory &mdash; it might not be necessary to know this to understand the solution, but it will be helpful. Basically, every integer is a point on the grid of infinite dimension...

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Быстрый старт в спортивное программирование Идет регистрация на открытый [онлайн-курс](http://rucode.net) «Быстрый старт в спортивное программирование». Над программой работали Владислав [user:veschii_nevstrui,2020-02-28] Невструев, Олег [user:snarknews,2020-02-28] Христенко, Филипп [user:DPR-pavlin,2020-02-28] Рухович и Илья [user:irkstepanov,2020-02-28] Степанов. Курс рассчитан на учащихся старших классов школы и студентов младших курсов технических специальностей. Для прохождения курса необходимо хорошо владеть основами одного из следующих языков программирования: С/С++, Java, Pascal/Delphi, Python (нужно уметь писать циклы, массивы, процедуры/функции и тому подобное). Курс начнется 2 марта 2020 года и будет рассчитан на четыре недели занятий. На один тематический модуль нужно будет потратить от двух до пяти часов в неделю. В день начала курса пройдет два открытых вебинара, на которых можно будет узнать подробности о программе. Время и ведущие:<br> [2 марта, 10:00](https://youtu.be/z5WEl6Hu4UU) (по московскому врем...

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Cheating in Educational Codeforces Round (92) Division 2 I noticed four users who have cheated in this Round (Educational Codeforces Round 92) and I want to name them here. I request the Codeforces community to take strict action against them those who degrade the quality of this beautiful platform. With internship season round the corner, Codeforces is often taken as an accountable platform by Companies and these people should be punished. Their handles are: [user:interview,2020-07-29] , [user:_krtky_,2020-07-29] ,[user:rahul16077,2020-07-29] [user:tempcfcfcf,2020-07-29] The first observation was the time at which the three users submitted their solutions. All of them submit solutions at almost the same time, thinking it wouldn't be noticed. I attach here a snippet. This is so disgusting. My proofs don't end here. Look at their submissions. They use very tactful tricks to avoid plagiarism checks, and I request the community here to take strict action on them. Please ban their accounts permanently. Their code snippets are almost ...

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Четвертьфиналы NEERC 2016 <img src="http://codeforces.me/predownloaded/92/eb/92ebeb1ab489ecd0bf7f300e0cab070b76f5c7d1.png" style="float:right; margin:0 1em 1em 1em;"> Совсем скоро пройдут четвертьфиналы NEERC 2016. В Саратовском ГУ он пройдет через неделю и мы сильно готовимся. А прямо сейчас наши команды пишут очередной тренировочный контест :) Всем, кто приедет в Саратов &mdash; привет, скоро увидимся! Чтобы вы не искали каждый раз дату очередного четвертьфинала NEERC, держите табличку [с сайта](https://neerc.ifmo.ru/information/calendar.html). Названия подрегионов кликабельны ;) По мере прохождения четвертьфиналов буду добавлять ссылки на результаты. |Контест|Город|Дата|Результаты| |-------|--------|-----|-| |[Северный подрегион](https://neerc.ifmo.ru/subregions/northern.html) |Санкт-Петербург | 22 октября 2016| <a href="http://neerc.ifmo.ru/archive/2016/northern/standings.html">Результаты</a> | |[Южный подрегион](http://contest.sgu.ru/) |Саратов |19 октября 2016|<a href="http://contest....

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XXII Командный чемпионат школьников Санкт-Петербурга по программированию <html> <body> <img src="https://lh4.googleusercontent.com/-h4YYP_THsWA/UoqFCzlfx8I/AAAAAAAAA4M/sP0Kg8G5s4I/w1269-h846-no/IMG_4089.JPG" align="right" style="height: 280px; margin: 20px;" alt="text"/> В конце ноября пройдет XV Всероссийская командная олимпиада школьников по программированию. Некоторые отборочные региональные соревнования уже прошли, и результаты уже подведены: - [Москва](http://ejudge.cs.msu.ru/stand-mkoshp-2014-a.html)<br> - [Екатеринбург](http://acm.urfu.ru/urcop/2014/standings.html)<br> - [Саратов](http://contest.sgu.ru/monitor/?id=3)<br> - [Рыбинск](http://www.rgata.ru/arch/acm_info_2014_6.pdf)<br> - [Пермь](http://ijudge.ru/)<br> - [Мурманск](https://yadi.sk/i/OtSZ3Ev1cRqSw)<br> В воскресенье 9 ноября 2014 года в Санкт-Петербурге в Университете ИТМО состоится Командный чемпионат школьников СПб по программированию. В соревновании будут участвовать более [90 команд](http://neerc.ifmo.ru/school/spb/listTeams.jsp). Информацию и расписание соревнований ...

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XVI Всероссийская командная олимпиада школьников по программированию <img src="http://codeforces.me/predownloaded/c5/c5/c5c59b61078d7236245ed021631cd7cad42da976.jpg" align="right" style="height: 220px; margin: 10px;" alt="text"/> Добрый вечер! Я рад вам сообщить, что в эти выходные пройдет шестнадцатая ВКОШП. В этом году олимпиада будет проходить на пяти площадках: в Санкт-Петербурге в здании Университета ИТМО, Барнауле, Алматы, Ташкенте и Тбилиси. Для участников завтрашний день начнется с регистрации, открытия и продолжится пробным туром. Основной тур соревнования начнется в [10:00](http://www.timeanddate.com/worldclock/fixedtime.html?msg=%D0%92%D0%9A%D0%9E%D0%A8%D0%9F+2015&iso=20151213T10&p1=352&ah=5) в воскресенье 13 декабря. Следите за текстовой трансляцией в твиттере [NEERCNews](https://twitter.com/NEERCNews) от [user:BudAlNik,2015-12-12], [user:qwerty787788,2015-12-12] и [user:subscriber,2015-12-12]. Подписывайтесь на наше [сообщество](https://vk.com/neercnews) в ВКонтакте, там будет много интересной информации. Смотрите [вид...

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Wrapping up the Global Rounds 2025 <img src="/predownloaded/2e/e2/2ee2f0f95f05aae6ca6f47812dae2dc2aabf277b.png" style="width: 240.0px;float: right;margin: 0 1.0em 1.0em 1.0em;max-width: 100.0%;max-height: 100.0%;"> Hello Codeforces, As 2025 comes to an end, it is time to start summing up the results. This post is about the Global Rounds. Since September, we have held a series of three Global Rounds, numbered from 29 to 31. This is the perfect moment to once again express our gratitude to XTX Markets for their initiative in organizing these rounds and their constant support over the years. Such stability in supporting the competitive programming movement is truly admirable and highly appreciated by the community. I wish XTX Markets a fantastic 2026, full of success and victories! In each of the three rounds, 50 t-shirts were awarded (to the top 30 participants and 20 random participants ranked between 31st and 500th). This year, we had to change the manufacturing and shipping process, so it is still a work...

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Atcoder 279G-At most 2 colors: Generating functions [Second-hand, Newbie Oriented]. **Part1: Introduction** [Atcoder Beginner Contest 279](https://atcoder.jp/contests/abc279) is good for learning [generating functions (GFs)](https://en.wikipedia.org/wiki/Generating_function). GFs could solve two of them (G and Ex). The English version tutorial of [279Ex](https://atcoder.jp/contests/abc279/tasks/abc279_h) has already been posted on the [MathStackExchange](https://math.stackexchange.com/questions/4586327/sum-of-product-of-min-which-is-related-to-the-pentagonal-number-theorem) by a kind person. Unfortunately, the English tutorial on [279G](https://atcoder.jp/contests/abc279/tasks/abc279_g) is not available. Now I would like to make a second-hand tutorial on [279G](https://atcoder.jp/contests/abc279/tasks/abc279_g) based on [PCTprobability's idea](https://atcoder.jp/contests/abc279/editorial/5293). I spend a huge amount of time understanding this idea. For contestants at about my level, it is quite difficult to understand [the idea](https://atcoder.jp/contests/abc27...

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IIOT — Open Contests 2018/19 For the second time, the _International Informatics Olympiads in Teams_ will be mirrored into online contests. These contests, of a **lower** difficulty level than those of the IOI, are intended for teams of 4 contestants from the same high school. However, everyone is welcome to participate to the mirror contests, especially if you are considering to join officially the IIOT in the future!  More specifically, we allow: - several teams from the same school (also in the official contest) - teams participating only in some contests (also in the official contest) - changes in team members - teams of students from different schools - smaller teams The mirror contests timing will be USACO-like: it will be open for 24 hours but you will be able to compete for up to **3 hours** (you can decide when to "start" your time window, after the login). Participation will be available upon registration to the Italia...

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Moscow Workshops Juniors 2021: first qualifying pre-New Year round!  We welcome high school students to take part in the programming boot camp **Moscow Workshops Juniors** that will be held on **February 24 – March 5** by Moscow Institute of Physics and Technology. The first qualifying online round (out of 3 or 4) will be open on **December 27 at 12:00** pm UTC+03. Moscow Workshops Juniors is the unique boot camp where students will be preparing for the **national competitions and international olympiads in informatics**. According to the statistics, 17 graduates of MWJ 2020 took part in the IOI and 11 of them won medals. Two years ago we started an **English-speaking group** at Moscow Workshops Juniors for students from Armenia, Azerbaijan, Bosnia and Herzegovina, Denmark, India, Italy, Syria, and Turkey. Last year guys from Netherlands and Romania also came to Russia. In total about 170 students participate in the boot camp every year. We would be glad to see everyone ag...

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Codeforces AI Assistant Have you ever wanted to analyze competitive programming data through simple, natural language queries? Or visualize rating progressions and performance patterns with ease? The **Codeforces AI Assistant** is a project designed to help the competitive programming community explore Codeforces data more effectively. Built as a learning initiative using Codeforces' public APIs, this tool aims to make competitive programming insights accessible to everyone. What It Does ------------ The **Codeforces AI Assistant** lets you explore competitive programming insights using simple, natural questions: - "Show me tourist's profile and recent performance" - "Find 1500-rated dp problems" - "Compare two users' rating progressions" - "Create a visualization of rating journey over time" Live Demo: -------------- #### Responses based on prompts: <spoiler summary=" Query: Create a comprehensive visualization and track of handle mishras839392 rating progression over time"> ![ ](/...

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From Tunisia to ICPC, Help Us Compete To Reach It! Hey Codeforces! We’re a team of three Tunisian students [user:Moyogi,2025-11-12], [user:Iceberg,2025-11-12] and [user:GH1hatem,2025-11-12] who share one dream, to compete at the Arab and African Collegiate Programming Championship (ACPC 2025), one of the most prestigious contests in our region and qualify to the ICPC World Finals. After months of intense training, sleepless nights, and thousands of practice problems, we qualified to represent Tunisia at ACPC!  Each of us has put years of effort into competitive programming. We all earned Gold Medals at the Tunisian Collegiate Programming Contest (TCPC), and one of us [user:Iceberg,2025-11-12] is already an ICPC World Finalist.  For us, this isn’t just a competition, it’s the result of countless hours of hard work, teamwork, and a deep love for problem-solving. It’s our chance to...

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Intra-Pilani Educational Contest : Editorial Thanks for participating! This is the first iteration in a series of educational contests held in BITS Pilani, Pilani Campus. The editorial for all seven problems is below. Open the hints one at a time before reading the rest. Contest link -> https://codeforces.me/contestInvitation/3ad0b848ae9e772cb849a80f90943647a6ee9b6c The problems were authored by [me](https://codeforces.me/profile/hzzt_2004), and tested by [user:keeshu,2026-10-26] and [user:Ultimateyagyik22,2026-10-26] Congratulations to the top 3: [user:sidat,2026-10-26], [user:ameasa,2026-10-26], [user:jagannathpisharody,2026-10-26]! <hr/> <b>A. AAAAAAAAAAAAAA</b> <spoiler summary="Hint 1"> Write the first few screaming numbers in decimal and see how each one relates to the previous one. </spoiler> <spoiler summary="Hint 2"> Adding one more digit $A$ on the right changes the number in a simple way. Can you simulate that directly, keeping everything modulo $10^9+7$? </spoiler> <spoiler summary="Obser...

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Is university degree important? <HTML> <HEAD> <META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=utf-8"> <TITLE></TITLE> <META NAME="GENERATOR" CONTENT="LibreOffice 4.1.6.2 (Linux)"> <META NAME="CREATED" CONTENT="20091123;224100000000000"> <META NAME="CHANGEDBY" CONTENT="Mahmoud Hassan"> <META NAME="CHANGED" CONTENT="20160315;170001200000000"> <META NAME="AppVersion" CONTENT="00.0001"> <META NAME="DocSecurity" CONTENT="0"> <META NAME="HyperlinksChanged" CONTENT="false"> <META NAME="LinksUpToDate" CONTENT="false"> <META NAME="ScaleCrop" CONTENT="false"> <META NAME="ShareDoc" CONTENT="false"> <STYLE TYPE="text/css"> <!-- @page { size: 8.5in 11in; margin: 1in } P { margin-bottom: 0.08in; direction: ltr; widows: 2; orphans: 2 } --> </STYLE> </HEAD> <BODY LANG="en-US" DIR="LTR"> <P STYLE="margin-bottom: 0.14in">I was going to write a short post asking you about your opinion on the importance of university degree but ended up writing a really long text about the educatio...

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Code League — National Competitive Programming Contest — Round 2 — Editorial Here is the link to the contest: [Link](https://codeforces.me/contestInvitation/f528fcc29732183e36f82a0adfdc6dbac0743f3f) ### [A. Free Coupon](https://codeforces.me/gym/690685/problem/A) <spoiler summary="Rate the Problem"> - **How good is this problem?** - Very Good - Good - Bad - Very Bad - **How hard is this problem?** - Very Easy - Easy - Hard - Very Hard </spoiler> <spoiler summary="Hint"> Which items should be taken using coupons? <spoiler summary="Answer"> Since a coupon can be used on any item regardless of its price, it is always best to use coupons on the most expensive items. This allows us to spend our coins only on cheaper items. </spoiler> </spoiler> <spoiler summary="Solution"> The problem asks us to find the maximum number of items Abenezer can obtain given $k$ coins, with the offer that every $b$ items bought with coins yiel...

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National Competitive Programming Challenge — Editorial Here is the link to the contest: [Link](https://codeforces.me/contestInvitation/6071a436743e70518e953453aadcf924bca069aa) ### [A. The Blacksmith](https://codeforces.me/gym/656191/problem/A) <spoiler summary="Credits"> - **Problem Idea**: [user:eulmelk,2025-12-12] - **Problem Setter**: [user:eulmelk,2025-12-12] </spoiler> <spoiler summary="Rate the Problem"> - **How good is this problem?** - Very Good - Good - Bad - Very Bad - **How hard is this problem?** - Very Easy - Easy - Hard - Very Hard </spoiler> #### Approach 1 <spoiler summary="Tutorial"> **Step 1**<br> $n \le 500$, so the total number of pairs is at most $\frac{n(n-1)}{2} = \frac{500 \cdot 499}{2} = 124750$. This is easily manageable within time limits. **Step 2**<br> By checking every possible pair, we never miss any valid combination. Therefore, keeping the maximum among all va...

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CF's secret that mike doesn't want you to know about^^ ok so i've been grinding for years now until i discovered this secret. it's honestly so shocking how this glitch isn't patched yet. I was thinking that this website is huge, surely someone should've discovered it, but to my surprise it still works. before you guys go judging my g [user:MikeMirzayanov,2022-02-04], it's not his fault, as it took me years.. no.. decades of searching to find this. so before i tell y'all this glitch i wanna show you my graph before knowing that it existed.  you might think that it's suspiciously similar to [user:sus,2022-02-04]'s graph, but i assure you that it's just a coincidence. now let me get into the real stuff. one sunny morning i was having a thought that there has to be a way, or a hack, some might say a glitch to gain a lot of rating in such a limited amount of time, and my thought was correct! there is a way, and it has something to do with y...

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Why Graph problems suck and how it takes away anime waifus from you. Helo, I am a fellow anime waifu lover and graph problems are ruining my life. Here is my story: I have been to a few onsite contests, and each and every one of them had graph problems. Coincidentally, the computer I was using was found to be destroyed after the contest. I can promise I have not done that. I am on the verge of insanity after facing all these uncultured graph problems. But you might be asking why graph problems are the seed of satan himself? Why do graph problems suck? Here’s my take on this: 1. They suck. 2. They suck really hard. 3. They break your computers. 4. Being good at graph problems makes you red, but we know that only experts get girlfriends. 5. Anime waifus hate graph problems (facts). <spoiler summary="Annoying Graph Problem 1">  </spoiler> <spoiler summary="Annoying Graph Problem 2">  </spoiler> <spoiler summary="Annoying Graph Problem 3">  </spoiler> <spoiler summary="Annoying Graph Problem 4">...

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Hack me! (CF Round #269, Div. 2) Hey there! I am testing some new stuff (according to your suggestions) and playing with matplotlib (learning it to be precise), so here is a bunch of statistics (only) in some past contest ([contest:471]). Previous posts can be found [here](http://codeforces.me/search?query=hackme). [cut] <h3>Stats</h3> By "rejected solutions" we understand solutions, which didn't pass the final tests (and were tested on them). Problem | <small>Successful hacks</small> | <small>Unsuccessful hacks</small> | Other | Sum | <small>Rejected solutions</small> | <small>Accepted solutions</small> | <small> All solutions on final tests</small>| :---:|:---:|:---:|:---:|:---:|:---:| <small> [problem:471A] </small> | 401 (55.08%) | 289 (39.70%)| 38 (5.22%) | 728 | 514 (18.02%) | 2338 (81.98%) | 2852 | <small> [problem:471B] </small> | 10 (13.16%) | 60 (78.95%)| 6 (7.89%) | 76 | 204 (10.01%) | 1834 (89.99%) | 2038 | <small> [problem:471C] </small> | 2 (6.06%) | 29 (87.88%)| 2 (6.06%) | 33 | 70 (...

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Codeforces Round #506 (Div. 3) &lt;copy-pasted-part&gt; Hello! [contest:1029] will start at [contest_time:1029]. You will be offered 6 or 7 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. Probably, participants from the first division will not be at all interested by this problems. And for 1600-1899 the problems will be too easy. However, all of you who wish to take part and have rating 1600 or higher, can register for the round unofficially. The round will be hosted by rules of educational rounds (extended ACM-ICPC). Thus, during the round, solutions will be judged on preliminary tests, and after the round it will be a 12-hour phase of open hacks. I tried to make strong tests &mdash; just like you will be upset if many solutions fail after the contest is over. You will be given 6 or 7 problems and 2 hours to solve them. Note that **the penalty** for the wrong submission in this round (and the following Div. 3 rounds) is **10 minutes*...

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A Nice Way to Visualize a Permutation Some people face difficulties in dealing with permutations. That's because they don't know what they really tell us. A permutation is any list of objects that have multiple arrangements, for example: & % # ! ! # & % ! & % # It doesn't necessarily have to be a sequence of numbers from 1 to n, you can just say that 92 45 23 52 45 92 52 23 are different permutations of some objects. Let's say we can only perform a swap between two objects, and we want to sort a permutation according to the sizes of our objects. 1 3 4 2 --> 1 2 4 3 --> 1 2 3 4 We aim at finding the minimum number of swaps to do so. We can view this problem as we want to place each object in a desired position, i.e., 1 has to be in the position 1, 2 has to be in the position 2, etc. If we have considered the positions as boxes and each object must return to its box, it might have created a visually simple graph: ![ ](/predownloaded/4f/b9/4fb96ebbe74b4e21930f78d0dd54c9e6840dc...

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Hack me! (Codeforces Round #281 (Div. 2)) <s>While waiting for [API](http://codeforces.me/api/contest.hacks?contestId=494) to update,</s> (it has been updated already) let's look at hacks in [contest:493]. That was really good round (even I had some hacks :)). Previous posts can be found [here](http://codeforces.me/search?query=hackme). [cut] <h3>Stats</h3> Problem | <small>Successful hacks</small> | <small>Unsuccessful hacks</small> | Other | Sum | <small>Solutions which can be hacked</small> | <small>Accepted solutions</small> | <small> All solutions on final tests</small>| :---:|:---:|:---:|:---:|:---:|:---:| <small> [problem:493A] </small> | 18 (22.50%) | 20 (25.00%)| 42 (52.50%) | 80 | 249 (13.16%) | 1643 (86.84%) | 1892 | <small> [problem:493B] </small> | 456 (62.81%) | 178 (24.52%)| 92 (12.67%) | 726 | 509 (29.84%) | 1197 (70.16%) | 1706 | <small> [problem:493C] </small> | 161 (47.35%) | 100 (29.41%)| 79 (23.24%) | 340 | 715 (58.56%) | 506 (41.44%) | 1221 | <small> [problem:493D] </small> | 22 (59.46%...

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Sharing my Happiness :) I am very very happy today. After 92 days of consistent grind, I became an expert. I wanted to share my analogy of code forces with Cricket which is my fav sport ( and whole India's fav as well ) Take Contests as balls. Something you will get Yorkers and sometimes you will get bouncers. Just try not to get out, take singles and doubles {Try to maintain your rating} And the day you get the full toss, mark it as your day and blast a six. Exactly that happened to me, I am good at certain topics and I am average ( for my rating ) in others I have previously solved a lot of 1800's binary search questions. Last Div. 3 I managed to solve the E problem since it was of Binary search. This Div2. contest I solved the D problem since it was number-theory based. Again a topic I am confident in. The key takeaway, no matter how much you suck right now, doesn't stop giving contests. Your rating will go down, no problem. All you need is 2 contests in your domain. Just wait ...

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Haskell solutions For those who are interested, here is a list of all problems for which Haskell solutions have been submitted. (Use the 'Status filter' to show only the Haskell submissions.) [1A](http://codeforces.me/problemset/status/1/problem/A) [1B](http://codeforces.me/problemset/status/1/problem/B) [1C](http://codeforces.me/problemset/status/1/problem/C) [2A](http://codeforces.me/problemset/status/2/problem/A) [2B](http://codeforces.me/problemset/status/2/problem/B) [2C](http://codeforces.me/problemset/status/2/problem/C) [3A](http://codeforces.me/problemset/status/3/problem/A) [3B](http://codeforces.me/problemset/status/3/problem/B) [3C](http://codeforces.me/problemset/status/3/problem/C) [3D](http://codeforces.me/problemset/status/3/problem/D) [4A](http://codeforces.me/problemset/status/4/problem/A) [4B](http://codeforces.me/problemset/status/4/problem/B) [4C](http://codeforces.me/problemset/status/4/problem/C) [4D](http://codeforces.me/problemset/status/4/problem/D)...

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Invitation to CodeChef Starters 92 (Rated till 6-stars ) - 31st May We invite you to participate in CodeChef’s [Starters 92](https://www.codechef.com/START92?utm_source=discuss&utm_medium=organic&utm_campaign=START92), this Wednesday, 31st May, rated till 6-stars Coders (ie. for users with rating < 2500). Time: [8:00 PM — 10:00 PM IST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=CodeChef+Starters+92&iso=20230531T20&p1=44&ah=2) Note that the duration is 2 hours. Read about the recent CodeChef changes [here](https://discuss.codechef.com/t/important-update/105637/3). Joining us on the problem setting panel are: - Setters: Irmuun [user:Irmuun.Ch,2023-05-31] Chinbat, Souradeep [user:souradeep.99,2023-05-31] Paul, Shikhar [user:TheDarkKnight,2023-05-31] Agrawal, Ayush [user:ayu_19,2023-05-31] Kumar, Shaurya [user:Shaurya_Bhalla,2023-05-31] Bhalla, Ziad [user:ZiadEl-Gafy,2023-05-31] El-Gafy - Testers: Nishank [user:IceKnight1093,2023-05-23] Suresh - Video Editorialists: Madhav [user:jhamadhav,2023-05-23] Jha, Suraj [user:jha...

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AVL дерево без больших вращений Добрый день! Скорее всего Вы когда-либо слышали про [AVL дерево](https://ru.wikipedia.org/wiki/%D0%90%D0%92%D0%9B-%D0%B4%D0%B5%D1%80%D0%B5%D0%B2%D0%BE). Помните, там есть большие вращения и маленькие? Большое, конечно, можно делать как два маленьких, просто оно называется большим. Вопрос: а есть ли тест, на котором дерево, построенное без использования больших вращений, имеет высоту хотя бы на 3 большую, чем правильное AVL дерево? А если нет теста, может, можно доказать корректность такого недо-AVL? =) Вот [код на C++](http://pastebin.com/xvMGwwFR), в котором <br> функция `void add( node* &t, int x );` делает правильное добавление в AVL-дерево, а<br> функция `void add_slow( node* &t, int x );` при нарушении инварианта всегда делает малое вращение. P.S. Ни программно, ни на бумажке у меня не получилось создать разницу высот больше двух, отсюда и вопрос. UPD: У кого-то были проблемы скачать/прочитать код, поэтому [not pastebin](http://acm.math.spbu.ru/~sk1/download/cod...

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Congratulations to AlRntn on becoming the youngest Iranian Grandmaster Congratulations to Ali Roueintan ([user:AlRnTn,2026-06-28]) on becoming the youngest Iranian Grandmaster. He is only in 9th grade. Well deserved.  His heatmap:  His solved problems: 

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Открытая олимпиада университета Иннополис по программированию 2015-2016 <img src="http://codeforces.me/predownloaded/60/c9/60c9b3061e917a215b866543dc166e851c9ea24f.jpg" align="right" style="height: 300px; margin: 20px;" alt="text"/> Привет всем! Рад вам объявить, что в этом сезоне состоится вторая [олимпиада университета Иннополис по программированию](http://olymp.innopolis.ru/) для школьников. Олимпиада пройдет в два этапа: два отборочных тура и финальный. Отборочные этапы нужно будет писать через интернет, результаты отборочных туров будут подводиться независимо. По результатам каждого из отборочных туров лучшие участники будут приглашены в финальный этап Открытой олимпиады университета Иннополис. Участвовать можно в любом из двух туров и даже в обоих турах, если у вас не получилось пройти в финал с первого. Туры проходят по правилам заключительного этапа Всероссийской олимпиады школьников по информатике. В олимпиаде могут принимать участие только школьники, условия задач всех этапов на русском языке. Первый отборочный тур состоится в [вос...

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Fun Sunday discovery I have just finished a virtual participation of [this Div 3](https://codeforces.me/contest/1619). At the end i have seen something strange to me.  There are three friends (i mean they are cp teammates) that were close on my friend scoreboard so i decided to have a look at their progression. Personally [user:FBI,2023-11-12] always inspire me to keep going as he started as a newbie ans is currently Candidate Master. Here are they and their graph progression : [user:FBI,2023-11-12]  [user:Pa_sha,2023-11-12]  [user:SashaT9,2023-11-12]  Another amazing thing is that their current level is so close. I'm still wandering if there are other friends that started cp at the same tim...

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Открытая олимпиада Университета Иннополис по программированию 2015-2016, второй отборочный тур <img src="http://olymp.innopolis.ru/upload/iblock/a0b/IMG_2056.jpg" align="right" style="height: 300px; margin: 20px;" alt="text"/> Всем привет. В эту [субботу, 19 декабря в 16:00 по московскому времени](http://www.timeanddate.com/worldclock/fixedtime.html?msg=%D0%92%D1%82%D0%BE%D1%80%D0%BE%D0%B9+%D0%BE%D1%82%D0%B1%D0%BE%D1%80%D0%BE%D1%87%D0%BD%D1%8B%D0%B9+%D1%82%D1%83%D1%80+%D0%9E%D1%82%D0%BA%D1%80%D1%8B%D1%82%D0%BE%D0%B9+%D0%BE%D0%BB%D0%B8%D0%BC%D0%BF%D0%B8%D0%B0%D0%B4%D1%8B+%D1%83%D0%BD%D0%B8%D0%B2%D0%B5%D1%80%D1%81%D0%B8%D1%82%D0%B5%D1%82%D0%B0+%D0%98%D0%BD%D0%BD%D0%BE%D0%BF%D0%BE%D0%BB%D0%B8%D1%81&iso=20151219T16&p1=352&ah=5), пройдет второй отборочный тур олимпиады Университета Иннополис. Участие могут принимать школьники, условия задач на русском языке. Олимпиада проводится по правилам Всероссийской олимпиады школьников по информатике. Для участия в отборочном туре нужно зарегистрироваться на [сайте](http://olymp.innopolis.ru/informatics/) до 23:59 18 декабря. В отбо...

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Lời giải cho Quy hoạch động [problem: 583720A] <spoiler summary = "Hint"> Kiểu dữ liệu `long long` sẽ không lưu được số Fibonacci thứ $92$. Như vậy, chúng ta sẽ phải dùng `unsigned long long`. </spoiler> <spoiler summary = "Code (C++)"> ```cpp #include<bits/stdc++.h> using namespace std; #define el '\n' #define int unsigned long long int f[100]; void solve(){ int n; cin >> n; cout << f[n] << el; } signed main(){ cin.tie(0) -> sync_with_stdio(0); f[0] = f[1] = 1; for(int i=2; i<=92; i++) f[i] = f[i - 1] + f[i - 2]; int tc = 1; cin >> tc; while(tc--) solve(); } ``` </spoiler> [problem: 583720B] <spoiler summary = "Hint"> + Với giới hạn lên tới $10^6$, việc duyệt qua từng số rồi tìm ước nguyên tố lớn nhất là không thể, vì ta sẽ mất $O(\sqrt n)$ để tìm ước, tức là xấp xỉ $10^3$ $\to$ tổng độ phức tạp sẽ là $O(10^9)$, vượt quá $1$ giây cho phép. + Để có thể tối ưu được thời gian, ta sẽ cần sử dụng Sàng Biến Đổi ở đây. Đầu tiên, ta sẽ ...

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[Tool] CommitForce: auto-sync your Accepted solutions to GitHub (no open tab, contest-safe) Hey Codeforces, Like many of you, I wanted an automated, hands-off way to back up all my Accepted solutions to GitHub so I could review my progress over time. However, after trying existing extensions out there, I kept running into recurring issues: * **Requiring an active Codeforces tab session:** Many tools rely on content scripts scraping the DOM. If you practice using CLion/VS Code, close your tabs, or submit through tools like Competitive Companion, sync fails. * **Hidden tabs popping up:** Some tools spawn pinned/hidden tabs (`chrome.tabs.create`), which break with `ACCESS_DENIED_ERROR` on contest submissions. * **Overwriting solutions:** Most tools key by Problem ID (e.g. `1872A.cpp`). If you solve a problem with brute force and later rewrite an optimized $O(N \log N)$ version or port it to Rust, your earlier Accepted attempt gets overwritten. * **Plagiarism risk:** Pushing solutions immediately to a public repository during live rated contests creates a real r...

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LET BOB COOK!!! Finally, justice has been served to Bob!! &#128557; In [2272F &mdash; Tree Reduction Game](https://codeforces.me/contest/2272/problem/F), Alice still gets the first move, but Bob finally gets some compensation: he can choose the initial root of the tree! With the right choice, Bob can guarantee his victory even when playing second. No more suffering from always going second — **Bob is finally getting his chance to shine!** Come on, Bob, you got this! &#128511; Upd: Bob really cooked this game. =DD <br> After a lot of research, the result surprised me <spoiler summary="chart:"> n is the number of nodes in the tree |n|samples|bob wins|alice wins|bob win rate| |-------|-----|-----------|-----|-----------| |2|1000|0|1000|0%| |3|1000|1000|0|100%| |4|1000|0|1000|0%| |5|1000|1000|0|100%| |6|1000|282|718|28.2%| |7|1000|1000|0|100%| |8|1000|463|537|46.3%| |9|1000|1000|0|100%| |10|1000|629|371|62.9%| |11|1000|1000|0|100%| |12|1000|735|265|73.5%| |13|1000|1000|0|...

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Coders of the month — July 2012 1- [user:iroro,2012-09-01]: 385<br/> * 119th in <a href="http://codeforces.me/contest/203/standings" target="_blank">Codeforces Round #128 (Div. 2)</a>: +59 (from <b><font color="blue">1607</font></b> to <b><font color="blue">1666</font></b>)<br/> * 6th in <a href="http://codeforces.me/contest/205/standings" target="_blank">Codeforces Round #129 (Div. 2)</a>: +87 (from <b><font color="blue">1666</font></b> to <b><font color="#A0A">1753</font></b>)<br/> * 62nd in <a href="http://codeforces.me/contest/213/standings" target="_blank">Codeforces Round #131 (Div. 1)</a>: +91 (from <b><font color="#A0A">1753</font></b> to <b><font color="#A0A">1844</font></b>)<br/> <br/> 2- [user:vlad107,2012-09-01]: 358<br/> * 42nd in <a href="http://codeforces.me/contest/204/standings" target="_blank">Codeforces Round #129 (Div. 1)</a>: +92 (from <b><font color="#FF8C00">1923</font></b> to <b><font color="#FF8C00">2015</font></b>)<br/> * 36th in <a href="http://codeforces.me/contest/213/standing...

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Rating (all) tab doesn't work I think that rating(all) tab on codeforces doesn't work. There is no difference between "rating" and "rating (all)" tabs. But for example there is [user:ershov.stanislav,2018-11-01] who should be in the top on "rating (all)" tab. [cut]   

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Участники удивляются тестам на RCC 2016 Q1 В воскресенье вечером завершился первый квалификационный раунд чемпионата Russian Code Cup 2016. Победил в этом раунде [user:subscriber,2016-05-09], а действующий чемпион RCC [user:Petr,2016-05-09] занял второе место. Полные результаты раунда <a href="http://www.russiancodecup.ru/en/championship/result/51/"> здесь</a>. На странице аккаунта во ВКонтакте участник [user:dkirienko,2016-05-09] <a href="https://vk.com/feed?w=wall27697_15094">удивляется прошедшему у него решению на основе рандома</a> по [задаче C](http://www.russiancodecup.ru/ru/championship/round/51/problem/C/): <img src="http://codeforces.me/predownloaded/f9/c0/f9c012d9e25dfd2378b3a8eecc9bd5987b8515c9.png"/> В комментариях Олег Мингалев указывает на простой тест против такого решения и факт того, что и у него зашло неправильное решение: <img src="http://codeforces.me/predownloaded/92/d4/92d461f762cc2a6e4c140326e141d03c146ec561.png"/> Удивительно &mdash; год назад случилась <a href="http://codeforces.me/bl...

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Botomania 2022 Greetings! We are proud to invite you to **Botomania 2022** as a part of **Threads, Felicity IIIT Hyderabad**! Botomania 2022 is 2-day long event where you'll write programs (bots) to play a two-player board game. The exact rules of the game will be revealed at the start of the contest. Your bot will go against bots written by other contestants. Don't worry if your bot isn't perfect, it can win as long as it can beat the other contestants' bot! You'll have 48 hours to make your bot, and improve upon it throughout the period of the event. <img style="float: center;text-aligh: center;width: 500px;height: 500px" src="/predownloaded/92/89/9289f1f0acfc9f5bd22424a4211f80ef53ce4f53.png"> You can visualize the games that your bot is playing on our website and analyze them to improve your bot! All the bots will compete against each other after the 48 hours in a final tournament where the strongest bot shall prevail! This is an individual event and only Python submissions will ...

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Изменение квот на NEERC Я хотел сесть писать этот пост, когда на официальном сайте появится список участников полуфинала, но так и не дождался этого момента. То ли оргкомитет считает, что и так все знают, какие команды прошли, а какие нет, то ли и сам не определился с этим. :) Поэтому не ругайте сильно, если я ошибочно считаю какую-то команду прошедшей/непрошедшей. Всё, что я пишу, касается только площадки в Питере. Если кто-то недоволен текущей системой квот на другой площадке, призываю вас написать свой пост. Итак, вспомним правила распределения квот: http://neerc.ifmo.ru/information/selection-rules.html. 1. Есть гарантированная квота каждого четвертьфинала, известная заранее (G + R + 2 в формуле), и надбавка 1 за каждые 50 команд-участников четвертьфинала. 2. Вуз может выставить максимум 2 команды, кроме единичных вузов, которые могут выставить 3. 3. В итоговом протоколе вычёркиваются все лишние команды вузов и первые Q выходят на полуфинал по правилам. 4. После этого ещё W команд получаю...

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Simple, Powerful VSCode C++ Setup for Windows and Ubuntu I was unable to find a simple yet powerful CP setup for my needs, so I decided to create one myself. I hope someone will find this useful. This setup uses C++ in VSCode with debugging support for users in Windows and Ubuntu. ## **Features** 1. VSCode ready to use out of the box (Only windows users need to correct MinGW installation path). 1. Run `.\windows-reset.bat` in Windows or `./ubuntu-reset.sh` in Ubuntu to reset the `Current` Folder. 1. All `.cpp` files automatically take input from `input.txt` and output to `output.txt` in the same folder. No need for complicated `ifdef`s. 1. Leverage powerful features of VSCode: * Step Through Debugging (Execute the code line by line, Hover over variables to get values) * Debug Console (View any object i.e. map, set, vector or any complex object) * Zen Mode (Utilize your screen to the fullest) Please feel free to post Issues/Suggestions at the Github Repository. [Github Repository](https://github.com/codeict/CP...

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How to test interactive problems using mkfifo Interactive problems are rare problems in competitive programming. I think that interactive problems are hard to solve for many guys. Because, testing for your solution is too hard. When testing interactivity, it is necessary to understand the stdin/stdout on your system. In this article, we will cover the following topics, - Basic code for interactive problems. How to do printf debugging. How to do testing by sample file. - The `mkfifo` that you often see in CodeForces user articles. mkfifo does not work on WSL1 as it is, but we will make it work on Windows with WSL1. - Colorful Result - (option) Use zsh + coproc to test without generating intermediate files. - <font color=red>The following examples are all in Python, but will work equally well in C++</font>. Similar articles can be found below. > [eku's article](https://codeforces.me/blog/entry/49490) This is introduction to useful tools (github) for interactive problems. ([user:eku,2020-12-31]) > [Gassa's Comment](h...

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Hack me! — Good Bye 2014! Still in buoyant humour after [contest:500]? While waiting for the editorial, maybe you would like to know why there were so many hacks in the last round of this year? As always, please share you thoughts, ideas or maybe hacks :) Previous posts can be found [here](http://codeforces.me/search?query=hackme). [cut] <h3>Stats</h3> Problem | <small>Successful hacks</small> | <small>Unsuccessful hacks</small> | Other* | Sum | <small>Solutions which can be hacked</small> | <small>Accepted solutions</small> | <small> All solutions on final tests</small>|<small>Hackers efficiency**</small>| :---:|:---:|:---:|:---:|:---:|:---:|:---:| <small> [problem:500A] </small> | 199 (40.61%) | 124 (25.31%)| 167 (34.08%) | 490 | 375 (9.32%) | 3650 (90.68%) | 4025 | 34.67% <small> [problem:500B] </small> | 738 (67.40%) | 214 (19.54%)| 143 (13.06%) | 1095 | 573 (24.89%) | 1729 (75.11%) | 2302 | 56.29% <small> [problem:500C] </small> | 0 (0.00%) | 9 (75.00%)| 3 (25.00%) | 12 | 23 (1.08%) |...

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Codeforces Global Rounds 2022: Final Results (GR19-GR24) Hello, Codeforces. It's time to take stock of last year. Shall we begin? And we are happy to sum up the results of the last season of Global Rounds. We announce the results! We remind you that the global rounds are a joint initiative of XTX and Codeforces. We hold 6 such rounds per year. All of them are open to both divisions. At each such round, 50 brand T-shirts were handed out, and we are happy to give T-shirts to all problem authors. The prizes for the 6-round series are: - 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. [cut] The final standings after six rounds (sorted by total points in four best-placed rounds): | Place | Contestant | = | GR 19 | GR 20 | GR 21 | GR 22 | GR 23 | GR 24| |--|--|--|--|...

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Stream week 2 I've got plans for at least 2 streams this week Today I will stream Educational Round 92 [15 minutes after it ends](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Egor%27s+stream+ep.+00&iso=20200729T1850&p1=168&ah=1&am=30) Tomorrow I'll stream Codeforces Round #660 [same time](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Egor%27s+stream+ep.+00&iso=20200730T1850&p1=168&ah=1&am=30) Join me on my [twitch channel](https://twitch.tv/egorcp). I would try to explain my thoughts during the contest and will answer questions from chat. You can ask any questions, not necessarily ones about these contests. UPD: stream started UPD2: stream ended, [here's VOD](https://youtu.be/TAebE-ZmQAU) UPD3: unfortunately I have to cancel stream today, hope there will be one next week

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ВКОШП 2013 Всем привет! В эти выходные (23-24 ноября) в Санкт-Петербурге, Барнауле, Алматы, Ташкенте и Тбилиси пройдет XIV Всероссийская командная олимпиада школьников по программированию (ВКОШП).<br/>По итогам региональных олимпиад и интернет-отбора для участия в ней приглашено более 200 команд. Из них в Санкт-Петербурге участвуют [100](http://neerc.ifmo.ru/school/russia-team/listTeamsFinal.jsp). Результаты, правила и расписание олимпиады в Санкт-Петербурге можно найти [здесь](http://neerc.ifmo.ru/school/russia-team/index.html). Обратите внимание на изменения в расписании! Для посещения олимпиады гостям необходимо [зарегистрироваться](https://docs.google.com/forms/d/1NcA-47s08dHSBwSdqNjWDwlrvxQQjW7iGpd69_YfFRI/viewform). Открытие и закрытие олимпиады можно будет смотреть [онлайн](http://www.ifmo.ru/online/). <br/>За новостями соревнований можно также следить в [твиттере](https://twitter.com/NEERCNews). Хештег олимпиады: [#ВКОШП](https://twitter.com/search?src=typd&q=%23%D0%92%D0%9A%...

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Codeforces Global Rounds 2019: Current Results After Four Rounds In 2019, with the support of XTX Markets, 6 rounds of the new Codeforces Global Rounds will be held. These will be common rounds for both divisions of 7–9 problems each. The duration of the rounds will be 2-3 hours, depending on the number and complexity of the problems. All such rounds will be rated for all participants. <i>At each such round, 50 brand T-shirts will be handed out, and we will be happy to give T-shirts to all authors and problem testers.</i> The prizes for the 6-round series in 2019: - 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. Current standings after four rounds: | Place | Contestant | = | Round 1 | Round 2| Round 3 | Round 4 | | - | - | - | - | - | - | - | | 1 | [user:tourist,2019-07-21] | 241...

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Notes on Codeforces Beta Round #92 Div2-A, B, C, D, E [problem:124A] Enumerate all the integers $i$ and find out those that satisfy both $i-1 \ge a$ and $n-i \le b$. [problem:124B] Generate all the feasible permutation patterns and find out the one under which the difference between the maximum number and the minimum integer is the smallest. [problem:124C] We divide the positions into the following sets. $A_2=(2, 4, 6,...,2m_1)$, $A_3=(3, 6, 9,...,3m_2)$, $A_5=(5, 10, 15,...,5m_3)$,... One can see that for any prime integer $p>2$, $A_p$ always has at least one common position with $A_2$, as long as the index $2p$ does not exceed the range. Thus, we find out the maximum such prime integer $p'$, and then count the total number of different positions belonging to sets $A_2, A_3,...A_{p'}$. These positions must have the same letters, while the other positions can have any letter. Therefore, the left work is to determine whether we have enough number of the same letter. [problem:124D] We first focus on the first conditi...

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Codeforces Watcher 1.8.5 (Christie): YouTube videos in Newsfeed Привет, Codeforces! Мы рады представить следующую версию приложения [Codeforces WatchR](https://github.com/xorum-io/codeforces_watcher), которая добавляет видео с избранных YouTube каналов о спортивном программировании в новостную ленту.  Обновленные приложения уже могут быть загруженны с [Google Play](https://play.google.com/store/apps/details?id=com.bogdan.codeforceswatcher) и [App Store](https://apps.apple.com/us/app/codeforces-watchr-contests/id1495591299). ### Список каналов Здесь приведен текущий список каналов, но мы будем рады добавить и другие каналы с интересным и полезным контентом: - [user:Errichto,2020-11-21] &mdash; https://www.youtube.com/channel/UCBr_Fu6q9iHYQCh13jmpbrg - [user:stefdasca,2020-11-21] &mdash; https://www.youtube.com/channel/UCyTPeByJ_FvAJljtc0svt-Q - [user:RomeoFantastik,2020-11-21] &mdash; https://www.youtube.com/channel/UC4LyqX6MVkg7NU2qBbvrkSg - [user:striver_79,2...

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2-CNF Problem — Doubts Hi I'm having trouble with the 2-CNF (Conjuctive Normal Form) problem, not just 2-SAT but the more general case of Conjuctive Normal Forms, ie: a => b (a implies b), c => ¬d (c implies not d). I've got some doubts, if you can help me with any of them it would help me a lot. 1 &mdash; What is the answer for the case (a => b) and (b => ¬a) and (¬a => c) and (c => d) and (d => ¬c)? I think its not satisfiable but if you solve like 2-SAT by just checking for all x if x and ¬x are in the same SCC then getting the variable with higher toposort between (x and ¬x) as the answer you may come to a diferrent result.  2 &mdash; There is an algorithm to find if some 2-CNF is solvable? And if its solvable how can we get some solution? 3 &mdash; If x or ¬x has not in edge nor out edge in the graph of implications, its correct to just set it as the answer? If you just get the toposort values like i...

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What are your favorite problems on codeforces? For coders who have learned computer science for years, there should be many hard problems you encountered in Codeforces. However, only some of them are memorable. Each of those problems became a vertebrae in the whole backbone which you lean on to solve other problems e.g. When I encountered [this problem](http://www.spoj.com/problems/MKTHNUM/) on spoj, I learned the idea about how to apply persistent segment tree and binary search on find k-smallest number => it helps me a lot, for example, in solving the problem E in Regional acm icpc 2016 in Bangkok. Because there are tons of problems on codeforces and core problems are not that plenty, I want to create a blog that sum up as many core problems as possible to help learners, from juniors to seniors, to shorten the time spending on finding good problems. So, please comment some problems that, in your perspective, are core problems. Thank you!!! ![ ](http://codeforces.me/predownloaded/92/7a/927ac1a9a29a893eeb9cd69b589125...

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Yandex Cup 2023 Algorithm Finalists Worldwide onsite finals became rare these days, but one of them, which is Yandex Cup 2023 Algorithm, will happen this weekend in Almaty, Kazakhstan. I've collected some statistics about finalists at the **Competitive Programming Hall of Fame** website: [link](https://cphof.org/advanced/ya_algo/2023) Also providing the list of participants that advanced to the final round here: | Yandex Handle | CF Handle | CF Rating | Country | Comment | |---------------|--------------|---------|-----------|-----| | [ecnerwala](https://cphof.org/profile/yandex:ecnerwala) | [user:ecnerwala,2023-12-01] | 3505 | United States | | | [hos.lyric](https://cphof.org/profile/yandex:hos.lyric) | [user:hos.lyric,2023-12-01] | 3119 | Japan | | | [maroon_kuri](https://cphof.org/profile/yandex:maroon_kuri) | [user:maroonrk,2023-12-01] | 3454 | Japan | | | [BatrrS](https://cphof.org/profile/yandex:BatrrS) | [user:998batrr,2023-12-01] | 2729 | Kazakhstan | | | [yahordubovik](https://cphof.org/profil...

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[Tutorial] Интересные модификации дерева Фенвика ## Дисклеймер Я нашел в интернете всего одну статью про [встречное дерево Фенвика](https://neerc.ifmo.ru/wiki/index.php?title=%D0%92%D1%81%D1%82%D1%80%D0%B5%D1%87%D0%BD%D0%BE%D0%B5_%D0%B4%D0%B5%D1%80%D0%B5%D0%B2%D0%BE_%D0%A4%D0%B5%D0%BD%D0%B2%D0%B8%D0%BA%D0%B0), которое должно расширять возможности обычного дерева Фенвика, и не смог ее понять. Однако недавно мне пришла в голову идея, как использовать [этот трюк](https://codeforces.me/blog/entry/74847) с двоичными подъемами, чтобы модифицировать дерево Фенвика и использовать его, например, для нахождения минимума на отрезке. Кроме того, я расскажу про еще одно дерево, достаточно схожее с деревом Фенвика. ## В чем вообще проблема и тот самый трюк Стандартное дерево Фенвика работает только на обратимых операциях (сумма, xor), так как мы быстро(за $\mathcal{O}(\log_2{n})$) можем получать значения только на префиксах. Оказывается, что за почти эту же асимптотику мы можем получать значения на любых отрезках. Чтобы лучше понимать, что ...

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Unknown Language Round #4: разбор задач <p>Итак, разбор задач. Лично для меня Befunge &mdash; один из тех языков, на которых горадо проще писать код, чем читать его (а уж искать баги в чужом &mdash; вообще каторга; в таком случае отсутствие взломов не может не радовать). Поэтому я ограничусь описанием общей идеи решения и приведением авторского кода &mdash; чисто чтобы показать, что автор не только издеваться над участниками горазд, но и сам решать может.</p> <h3>A. Шестиугольные числа</h3> {{{&amp;:2*1-*.@}}} <p>&quot;Утешительная&quot; задача, требующая только понимания принципа работы со стеком. Дублируем прочитанное число $n$, верхнюю копию умножаем на 2 и вычитаем из результата один &mdash; теперь в стеке два числа $n$ и $2n - 1$. Перемножаем их и выводим на печать.</p> [cut] <h3>B. Gnikool Ssalg</h3> {{{&gt; ~ : 25*- #v_ $ &gt;:#,_ @ ^ &lt;}}} <p>Здесь проще всего воспользоваться основным свойством стека &mdash; элементы вынимаются из него в порядке, обратном тому, в котором их складывали. Решение разбивает...

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Results of IZhO 2018! Hello Codeforces! ------------------ Here is detailed overview of results of IZhO 2018: <br> <br> There was 2 round each 5:00:00 long with 3 problems. The second round time was increased for 15 minutes because of some problems with one of tasks. IOI rules. <br> <br> <ul> <li> <b>137</b> participants took part in the competition </li> <li> Highest result is <b>549</b> points and it was received by Roman Korobkov ([user:romanasa,2018-01-14]) </li> <li> The first five winners are: </li> <ol> <li> Roman Korobkov &mdash; Russia &mdash; [user:romanasa,2018-01-14] </li> <li> Gainullin Ildar &mdash; Russia &mdash; [user:300iq,2018-01-14] </li> <li> Karneichyk Mark &mdash; Belarus &mdash; [user:markysha,2018-01-14] </li> <li> Anoprenko Mikhail &mdash; Russia &mdash; [user:manoprenko,2018-01-14] </li> <li> Kairly Nurlykhan &mdash; Kazakhstan &mdash; [user:Nurlykhan,2018-01-14] </li> </ol> </ul> <br> <br> [cut] There is full table of results and submits: <br> <br> [Table...

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Atcoder 'D' Tasks getting difficult Hi, Lately , I am not able to even touch the atcoder 'D' tasks , Last Regular round , which was Regular round 93 , there was a nice thinking 'D' task which was a constructive algorithm problem and I was not able to solve it. . Same was the case in the last to last regular round on Atcoder. . Round 92 , Task D &mdash; Two Sequences . . The problem is I have come to realize that maybe problems of these types are in general hard for me and I should train on them more , I am weak at greedy problems and constructive algorithm problems . . Are there any other places except for Atcoder where I can practice problems similar to Atcoder problem D ? I want to become fast and accurate at solving D , particualrly greedy and constructive , but I cant find the same quality problems anywhere except for atcoder , and the quantity of problems there is very less , Please help me. I need problems similar to Atcoder D for practice! Also tell me some good sources to practice my gree...

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