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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Every Technique and Algorithm I Used to Become Grandmaster Hi everyone, I became grandmaster today so I decided to go down memory lane and review every problem I have ever done in a CodeForces contest to look back and see every technique and algorithm I had to use to become a grandmaster. I am not sure how useful this is, I mostly think it's fun to look at all the old solutions I wrote and how different it was from how I write code now. The main takeaway is that, as many people have said before, you don't need to know or memorize a bunch of advanced algorithms to become grandmaster. As you will see, there are many problems where I just used "ad hoc reasoning," meaning there's not a standard technique I used to solve the problem and you just need to make some clever mathematical observations to solve the problem. Also, there are many popular algorithms that I have never needed in a CodeForces contest despite being a grandmaster: - Sparse tables, Fenwick trees, and segment trees - String algos, like rolling hashes, Knuth-Morris-Pratt, suffix...

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Codeforces Round #570 Solutions Since it will be a little while longer before the editorials for the recent Division 3 Round come out, I thought I'd post some solutions I wrote up. Please feel free to post below if you have any questions or notice any errors. If any of my solutions end up getting hacked, I'll replace the submission and solution text as soon as possible. Links to my submissions are at the bottom of this post. --- **A:** We can easily prove that the answer will not be much bigger than A, so simply iterating through all the possible values until we find one that works will do fine. (As a trivial proof, note that 1003 is interesting, so we will have to test at most 1003 numbers.) Then, the only challenging part from here is finding the sum of the digits of a number, which can be implemented easily with modular arithmetic. --- **B:** Start by sorting the prices. It turns out that only the greatest and least prices matter. We have two key facts to prove: 1. The answer is -1 if the ...

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Codeforces Round #570 (Div. 3) &lt;almost-copy-pasted-part&gt; Привет! В [contest_time:1183] начнётся [contest:1183] &mdash; очередной Codeforces раунд для третьего дивизиона. В этом раунде будет 6 или 7 задач (или 8), которые подобраны по сложности так, чтобы составить интересное соревнование для участников с рейтингами до 1600. Однако все желающие, чей рейтинг 1600 и выше могут зарегистрироваться на раунд вне конкурса. Раунд пройдет по правилам образовательных раундов. Таким образом, во время раунда задачи будут тестироваться на предварительных тестах, а после раунда будет 12-ти часовая фаза открытых взломов. Я постарался сделать приличные тесты &mdash; так же как и вы буду расстроен, если у многих попадают решения после окончания контеста. Вам будет предложено 6 или 7 (или 8) задач и 2 часа на их решение. **Штраф** за неверную попытку в этом раунде (и последующих Div. 3 раундах) будет равняться **10 минутам**. [Напоминаем](/blog/entry/59228), что в таблицу официальных результатов попадут только <i...

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SEERC 2021 and Grand Prix of Southeastern Europe  Hi everyone! 2021 Southeastern Europe Regional Contest took place on November 21. [Here](http://acm.ro/) you can view the full standings. Congratulations to the winners of the contest! | Place | Team Name | Contestant 1 | Contestant 2 | Contestant 3 | Problems | Penalty | | - | - | - | - | - | - | - | | 1 | [Taras Shevchenko National University of Kyiv] KNU_0_GB_RAM | [user:KostasKostil,2021-11-26] | [user:VladProg,2021-11-26] | [user:kostia244,2021-11-26] | 13 | 1788 | | 2 | [Kharkiv National University of Radio Electronics] KhNURE_Energy is not over | [user:BigBag,2021-11-26] | [user:Barichek,2021-11-26] | [user:Mustang98,2021-11-27] | 12 | 1274 | | 3 | [Lviv National University] LNU Bulldogs | [user:mshcherba,2021-11-26] | [user:Vasyl_Protsiv,2021-11-26] | [user:PetroTarnavskyi,2021-11-26] | 11 | 1429 | | 4 | [Faculty of Computer Science, Belgrade] GII Klub | [us...

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Codeforces Round #531 (Div. 3) Happy New Year to all of you! So, meet another round from blue :) &lt;copy-pasted-part&gt; Hello! [contest:1102] will start at [contest_time:1102]. 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 submis...

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How to become red. 01. Can a gray one become red? The most popular question on Codeforces must be "How to become red". I've just (February 2021) ran a script and discovered that the current number of Codeforces profiles is 323553. Only 1622 profiles have in their history a rating more than 2400. [cut] I should say, not as many reds as I expected. [My script on github.](https://github.com/NataIss/codeforces) I hope you remember that a newcomer used to start with 1500 points. I selected users who fell down to the grey level but did not give up and later became red. Let me introduce these 40 brave guys: - [user:Aleks5d,2021-02-19] min 1195 max 2683 - [user:Ali.Kh,2021-02-19] min 1167 max 2600 - [user:Alpha_Q,2021-02-19] min 999 max 2452 - [user:Arpa,2021-02-19] min 1057 max 2679 - [user:Arthur,2021-02-19] min 1158 max 2592 - [user:Atreus,2021-02-19] min 1134 max 2729 - [user:Bench0310,2021-02-19] min 1158 max 2502 - [user:CTPAX,2021-02-19] min 1188 max 2416 - [user:Danylo99,2021-02-19] min 1195...

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This is a blog to track my consistency I often struggle with consistency, so I’ve decided to update this blog daily by listing the questions I solve each day. Date- 24/06/2025 https://codeforces.me/problemset/problem/1771/B https://codeforces.me/problemset/problem/1759/D https://codeforces.me/problemset/problem/1714/E Date- 25/06/2025 https://codeforces.me/problemset/problem/1648/A Date- 26/06/2025 https://codeforces.me/problemset/problem/1519/C Date- 27/06/2025 https://codeforces.me/contest/1520/problem/E https://codeforces.me/contest/1701/problem/C Date- 28/06/2025 https://codeforces.me/contest/1374/problem/D https://codeforces.me/contest/1362/problem/C Date- 29/06/2025 https://codeforces.me/contest/1350/problem/B https://codeforces.me/contest/1320/problem/A Date- 30/06/2025 https://codeforces.me/contest/1183/problem/D https://codeforces.me/contest/268/problem/C Date- 01/07/2025 https://codeforces.me/contest/1903/problem/C Date- 02/07/2025 https://codeforces.co...

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Guess The Statement: Codeforces game I recently invented a new game called Guess the Statement. Here's how it works: 1. Open up a Div. 4 or Div. 3 or Educational. 2. Do **NOT** read any of the tasks. 3. Open the editorial. 4. For each task, read the code, and try to guess what the statement was. 5. Read the tasks and see how close you were! Recommended contests to start with: - [contest:1850] - [contest:1915] - [contest:1183] - [contest:1000] I believe this is the only way to enjoy low-rated problems.

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Getting WA in LightOJ 1183 — Computing Fast Average ( Segment Tree problem) [Problem](http://www.lightoj.com/volume_showproblem.php?problem=1183) [Solution](https://ideone.com/RnGhOS) I have matched all forum I/O. All O/Ps are matched correctly. But still getting Wrong Answer. Can anyone please tell where I did mistake ? **Problem Description:** Given an array of integers (0 indexed), you have to perform two types of queries in the array. 1. 1 i j v &mdash; change the value of the elements from ith index to jth index to v. 2. 2 i j &mdash; find the average value of the integers from ith index to jth index. You can assume that initially all the values in the array are 0. **Input** Input starts with an integer T (≤ 5), denoting the number of test cases. Each case contains two integers: n (1 ≤ n ≤ 105), q (1 ≤ q ≤ 50000), where n denotes the size of the array. Each of the next q lines will contain a query of the form: 1 i j v (0 ≤ i ≤ j < n, 0 ≤ v ≤ 10000) 2 i j (0 ≤ i ≤ j < n) **Output** For each case, print t...

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Can You help me with 1183E ? Question : [https://codeforces.me/contest/1183/problem/E](https://codeforces.me/contest/1183/problem/E) I want to know how it can be done using 1.Graphs 2.Dynamic Programming Also there is a harder version of the problem. [problem:https://codeforces.me/contest/1183/problem/H] What changes do i need to make for this in my approach? P.S my rating is 1600. Any help is appreciated Thanks

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All Div3's Links This is for boosting the speed and have good commonds with the tricky implementations There are many Div. 3 will come and I will also try my best to keep this blog update. Although if you want to generate these links at any time locally you can find the code on my GitHub repo: https://github.com/adshin21/Codeforces-Contest-Selector-By-Div-s So I've collected the links for all the Div. 3's that has happened. <table class = "bordertable"> <tbody> <tr> <td> Div3 Round 1 </td> <td> <a href=http://codeforces.me/contest/977>http://codeforces.me/contest/977</a></td> </tr> <tr> <td> Div3 Round 2 </td> <td> <a href=http://codeforces.me/contest/978>http://codeforces.me/contest/978</a></td> </tr> <tr> <td> Div3 Round 3 </td> <td> <a href=http://codeforces.me/contest/988>http://codeforces.me/contest/988</a></td> </tr> <tr> <td> Div3 Round 4 </td> <td> <a href=http://codeforces.me/contest/999>http://codeforces.me/contest/999</a></td> </tr> <tr> <td> Div3 Round 5 </td> <t...

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Reporting a Small Bug Just wanted to report a bug regarding those two problems rating and found out that both the announcement and the editorial had 100+ comments so decided to write this. The [easy version](https://codeforces.me/contest/1183/problem/E) is rated 2000 while the [hard version](https://codeforces.me/contest/1183/problem/H) is rated 1900 (the only differences is that the constraints in H are larger). Thanks!

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UVA 10242 — NEEDED HELP ~~~~~ #include<bits/stdc++.h> using namespace std; int main() { float x1,x2,y1,y2,x3,y3,x4,y4,ansx,ansy; while(cin>>x1>>y1) { cin>>x2>>y2>>x3>>y3>>x4>>y4; if(x1==x3 && y1==y3) { ansx = x2-x1+x4; ansy = y2-y1+y4; } else if(x2==x3 && y2==y3) { ansx = x1-x2+x4; ansy = y1-y2+y4; } else if(x1==x4 && y1==y4) { ansx = x2-x1+x3; ansy = y2-y1+y3; } else { ansx = x1-x2+x3; ansy = y1-y2+y3; } printf("%.3lf %.3lf\n", ansx, ansy); } } ~~~~~ i dont know whats wrong with code , getting wrong answer. if anyone can point out some problem in the code. thank you in advance. [Link to problem](https://uva.onlinejudge.org/index.php?option=onlinejudge&page=show_problem&problem=1183)

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[Video]: 3 different ways to count distinct subsesquences ft. CF1183H I created a video on 3 different techniques to count distinct subsequences of a string. * $O(N^3)$ Lexicographic Minimal DP on Indices * $O(N^2)$ Lexicographic Maximal Character DP * $O(N^2)$ Lexicographic Maximal PIE DP Video https://youtu.be/DZ8sVn4W6IQ Practice Problem [H. Subsequences (hard version)](https://codeforces.me/contest/1183/problem/H)

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Contests hack statistics (Number of hacks by round) Just felt like gathering some data about hacks. Parsed around ~400 last contests Probably it would be worth it to also include SFT, but whatever Educational 96 is not finished yet but also whatever Last 100 ------------------ **847** Educational Codeforces Round 96 (Rated for Div. 2) **30** Codeforces Global Round 11 **248** Codeforces Round #674 (Div. 3) **0** 2020 ICPC, COMPFEST 12, Indonesia Multi-Provincial Contest (Unrated, Online Mirror, ICPC Rules, Teams Preferred) **97** Bubble Cup 13 &mdash; Finals [Online Mirror, unrated, Div. 2] **86** Bubble Cup 13 &mdash; Finals [Online Mirror, unrated, Div. 1] **20** Codeforces Round #675 (Div. 2) **1** Codeforces Round #672 (Div. 2) **70** Codeforces Round #671 (Div. 2) **58** Educational Codeforces Round 95 (Rated for Div. 2) **3** Codeforces Round #673 (Div. 2) **11** Codeforces Round #673 (Div. 1) **73** Codeforces Round #667 (Div. 3) **121** Grakn Forces 2020 **4** Co...

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All DIV 3 contests links for practice Hello friends I am sharing the link of all div 3 links for practice. -------------------------------------------------------------------- <br><br> Div3 1: https://codeforces.me/contest/977<br> Div3 2: https://codeforces.me/contest/978<br> Div3 3: https://codeforces.me/contest/988<br> Div3 4: https://codeforces.me/contest/999<br> Div3 5: https://codeforces.me/contest/1003<br> Div3 6: https://codeforces.me/contest/1005<br> Div3 7: https://codeforces.me/contest/1006<br> Div3 8: https://codeforces.me/contest/1015<br> Div3 9: https://codeforces.me/contest/1029<br> Div3 10: https://codeforces.me/contest/1066<br> Div3 11: https://codeforces.me/contest/1077<br> Div3 12: https://codeforces.me/contest/1092<br> Div3 13: https://codeforces.me/contest/1095<br> Div3 14: https://codeforces.me/contest/1102<br> Div3 15: https://codeforces.me/contest/1108<br> Div3 16: https://codeforces.me/contest/1118<br> Div3 17: https://codeforces.me/contest/113...

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Simple training for beginners Hello everyone! I have set up a training for beginners, The training focuses on solving various problems on Codeforces. Training that contains: 100 Problems (<span style = "font-weight: bold;">A</span>) and 100 Problems (<span style = "font-weight: bold;">B</span>). and 50 Problems (<span style = "font-weight: bold;">C</span>). Problems Difficulty: from <span style = "font-weight: bold;">800</span> to <span style = "font-weight: bold;">1500</span>. Problems links: <spoiler summary="100 Problems A"> <ol> <li><a href = "https://codeforces.me/problemset/problem/231/A">Problem 1</a></li> <li><a href = "https://codeforces.me/problemset/problem/228/A">Problem 2</a></li> <li><a href = "https://codeforces.me/problemset/problem/236/A">Problem 3</a></li> <li><a href = "https://codeforces.me/problemset/problem/233/A">Problem 4</a></li> <li><a href = "https://codeforces.me/problemset/problem/214/A">Problem 5</a></li> <li><a href = "https://codeforces.me/problemse...

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Timus #1183 : Bracket Sequence Can anybody provide me a hint for this [problem](http://acm.timus.ru/problem.aspx?space=1&num=1183). I am not able to get what the dp states should be. Thanks in advance.

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The entire cses problem set sorted by the number of solvers! I could not find it online so I made it myself, I hope you will find it useful! Problem : Number of solvers - Weird Algorithm : 73338 - Missing Number : 62177 - Repetitions : 54281 - Increasing Array : 50436 - Permutations : 44614 - Distinct Numbers : 33154 - Dice Combinations : 32886 - Number Spiral : 31522 - Bit Strings : 29957 - Minimizing Coins : 28281 - Trailing Zeros : 28124 - Coin Combinations I : 26104 - Two Sets : 25446 - Coin Piles : 24696 - Apartments : 24318 - Removing Digits : 24291 - Two Knights : 23643 - Grid Paths : 23168 - Ferris Wheel : 23109 - Counting Rooms : 22561 - Palindrome Reorder : 22339 - Coin Combinations II : 22133 - Sum of Two Values : 21004 - Maximum Subarray Sum : 20797 - Book Shop : 20376 - Creating Strings : 19359 - Building Roads : 19197 - Restaurant Customers : 18982 - Concert Tickets : 18507 - Apple Division : 18503 - Stick Lengths : 18339 - Movie Festival : 17839 - Message Route : 16337 - Building Teams : 1578...

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Dp problem) Hello Codeforces :) It's again me! Please help me with this problem -> [link](http://acm.timus.ru/problem.aspx?space=1&num=1183)

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Help! Why do I get the "division by zero" error in this? https://codeforces.me/contest/1183/submission/56306470 I will be more than appreciated if you help me!

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First Ever Users to Reach Some Rating Milestones Revised: ratings below 1500 and greatest rises Several days ago I published a [table](https://codeforces.me/blog/entry/104320) with first people to reach certain ratings. It featured only ratings above 1500, and [user:adamant,2022-07-09] advised to do the same, but on achieving ratings below 1500. I found it quite interesting, and, after several days of collecting data about participations of 447911 Codeforces users, I finally made this table. [cut] For several reasons I firstly put another table. This is the table of greatest rating rises in the history of Codeforces. The reasons are: 1. I have collected so much data from Codeforces that it would be blasphemy not to use it in as many ways as possible. 2. These tables might intersect a lot: it's easier to get a terrific rise in ratings if you are low-rated. (Many people abuse this and deliberately get very low-rated to make a great jump.) 3. Someone recently posted a table with greatest rating rises and falls. I wasn't able to find this table to check whether it was...

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Milestones: ratings below 1500 and greatest rises (2024 edition) <i>Note.</i> This is an updated version of [this post](https://codeforces.me/blog/entry/104683). If you like [this style](https://codeforces.me/blog/entry/104320) more, please tell me in the comments. Since [user:tourist,2024-09-05]'s [breakthrough](https://codeforces.me/blog/entry/133401), I've received a lot of requests to update my old posts with rating achievements. However, I wasn't able to do it immediately since my method of doing it requires to download the rating change history of every user, which, in turn, requires to perform several hundred thousand requests to Codeforces, about which the website (and Cloudflare) is not happy. It took more that three days, but finally the job is done! Below are two tables. The first one is the greatest positive rating changes. The second one is the first users ever to reach some rating value. [cut] <table> <tr> <th>Place</th> <th>&Delta;</th> <th>Person</th> </tr> <tr> <td>1^st</td> <td><b>1182<...

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