Educational Codeforces Round 120 [рейтинговый для Div. 2] Привет, Codeforces! В [contest_time:1622] состоится [contest:1622]. Продолжается серия образовательных раундов в рамках инициативы [Harbour.Space University](https://harbour.space/)! Подробности о сотрудничестве [Harbour.Space University](https://harbour.space/) и Codeforces можно прочитать <a href="http://codeforces.me/blog/entry/51208">в посте</a>. Этот раунд будет **рейтинговым для участников с рейтингом менее 2100**. Соревнование будет проводиться по немного расширенным правилам ICPC. Штраф за каждую неверную посылку до посылки, являющейся полным решением, равен 10 минутам. После окончания раунда будет период времени длительностью в 12 часов, в течение которого вы можете попробовать взломать абсолютно любое решение (в том числе свое). Причем исходный код будет предоставлен не только для чтения, но и для копирования. Вам будет предложено **6 или 7 задач на 2 часа**. Мы надеемся, что вам они покажутся интересными. Задачи вместе со мной придумывали и готовили Адилбек [...

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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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Edu CF Round 120 Unofficial Editorial [Construct A Rectangle](https://codeforces.me/contest/1622/problem/A) <spoiler summary="A Editorial"> Let the stick lengths be $X, Y, Z$. The broken stick $X$ either forms two parallel sides or two perpendicular sides. In the first case, $X$ is even and $Y == Z$. In the second case, $X == Y+Z$. We try all choices of $X$. [A Solution](https://codeforces.me/contest/1622/submission/140867573) </spoiler> [Berland Music](https://codeforces.me/contest/1622/problem/B) <spoiler summary="B Editorial"> Say we dislike $L$ songs &mdash; those $L$ songs must have unique ratings $q_i$ from $1$ to $L$. To minimize the sum of $\|p_i - q_i\|$, we should keep $q_i$ in the same order as $p_i$. [B Solution](https://codeforces.me/contest/1622/submission/140868181) </spoiler> [Set or Decrease](https://codeforces.me/contest/1622/problem/C) <spoiler summary="C Editorial"> Optimal strategies can be described by $(x, k)$: decrease the lowest value by $x$, then set the largest $k...

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CSES sorted by number of solves 98870 https://cses.fi/problemset/task/1068 84128 https://cses.fi/problemset/task/1083 73464 https://cses.fi/problemset/task/1069 68570 https://cses.fi/problemset/task/1094 60297 https://cses.fi/problemset/task/1070 46283 https://cses.fi/problemset/task/1621 45685 https://cses.fi/problemset/task/1633 42682 https://cses.fi/problemset/task/1071 40314 https://cses.fi/problemset/task/1617 39319 https://cses.fi/problemset/task/1634 37742 https://cses.fi/problemset/task/1618 36164 https://cses.fi/problemset/task/1635 34591 https://cses.fi/problemset/task/1092 33748 https://cses.fi/problemset/task/1084 33562 https://cses.fi/problemset/task/1637 33225 https://cses.fi/problemset/task/1754 32099 https://cses.fi/problemset/task/1090 32004 https://cses.fi/problemset/task/1072 31920 https://cses.fi/problemset/task/1638 31209 https://cses.fi/problemset/task/1192 30358 https://cses.fi/problemset/task/1636 30329 https://cses.fi/problemset/t...

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Congratulations to Sparky_Master_WCH1226 Dear [user:Sparky_Master_WCH1226,2022-04-19], Congratulations for reaching <span class="user-red">Grandmaster</span> and gaining your brand new <span class="user-red">red</span> name <span class="rated-user user-red">Sparky_Master_WCH1226</span>!!! We have been so used to seeing <span class="rated-user user-orange">Sparky_Master_WCH1226</span> ever since you became <span class="user-orange">Master</span> in [contest:1623], less than 24 hours after you reached <span class="user-violet">Candidate Master</span> in [contest:1622]. While red is a nice colour, it is quite sorrowful to say goodbye to the familiar <span class="rated-user user-orange">Sparky_Master_WCH1226</span>. Goodbye, goodbye, goodbye, we will remember <span class="rated-user user-orange">Sparky_Master_WCH1226</span> forever... Unless, of course, if it occurs that our beloved (or shall I say, much loathed?) <span class="rated-user user-red">Sparky_Master_WCH1226</span> decides to go back to the familiar <span clas...

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Codeforces rating deflation <div align="right"> <table> <tr> <td align="left"><em> &mdash; You know what they call an International Grandmaster in 2026?<br> &mdash; They don't call it an International Grandmaster?<br> &mdash; No, man, they got the AI there, they wouldn't know what International Grandmaster is.<br> &mdash; What'd they call it?<br> &mdash; They call it International Master. </em></td> </tr> </table> </div> ### Introduction There was a heated discussion recently, and I decided to quantify the rating deflation over the recent 1.5 years. After accounting for natural improvement, I found roughly 150-190 rating points of deflation. The following is the rating gap between AI period and pre-AI period.  ### Background - We need to estimate the recent rating dynamics and compare it with pre-AI dynamics. - Participants have natural improvement when they train, especially lower rated...

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Almost same Submissions yielding different results. Hi Codeforces, I was trying to solve yesterday's [problem:1622C] and made [this submission](https://codeforces.me/contest/1622/submission/140860168) which failed at test case 3 but after a bit of cleaning up In code I made [this submission](https://codeforces.me/problemset/submission/1622/140860992) and this was accepted. Can anyone please help me and explain why this happened?

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B. Berland Music [Link to problem](https://codeforces.me/contest/1622/problem/B)  [Link to code:](https://ide.geeksforgeeks.org/tFepLHQ3AJ) Any suggestions, corrections, or optimizations to code are welcomed :)

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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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Graph saving methods Hi. ## Introduction. We have a graph, we want to save it (and maybe run DFS on it for example); simple? Yes, but I want to show different methods for this, you can choose any of them depending on problem. ### Adjacency matrix. Simple, if graph is not weighted, save in $G[v][u]$ if there is an edge between $v$ and $u$ or not. If graph is weighted, if there is an edge between $v$ and $u$ save it’s weight in $G[v][u]$, save $-1$ otherwise (if weight can be negative, use $inf$ instead of $-1$). Memory usage : $\mathcal{O}(n ^ 2)$.<br>Overall time complexity : $\mathcal{O}(n ^ 2)$ (for running dfs). <spoiler summary="Code here"> ~~~~~ // God & me #include <bits/stdc++.h> using namespace std; const int maxn = 1e3 + 17; int n, m; bool G[maxn][maxn], mark[maxn]; void dfs(int v){ if(mark[v]) return ; mark[v] = 1; for(int u = 0; u < n; u++) if(G[v][u]) dfs(u); } int main(){ ios::sync_with_stdio(0), cin.tie(0); cin >> n >> m; ...

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A question on Educational Codeforces Round 120 problem D Link to the problem: [https://codeforces.me/problemset/problem/1622/D](https://codeforces.me/problemset/problem/1622/D) In this problem's editorial, they mention that there is an O(N) solution that work with this problem, and now I'm curious to learn it. Can anyone help me ?

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Teams of NDUB IUPC 2026  Notre Dame University Bangladesh is set to host an Inter University Programming Contest on 15-16 May, 2026. Across Bangladesh, the strongest teams rise to compete. Below is the list of participating teams, along with their institutions, members, and the maximum team rating, calculated using the [CF team rating algorithm](https://codeforces.me/blog/entry/16986). Best wishes to everyone preparing for NDUB IUPC 2026 — looking forward to meeting you all! <table> <thead> <tr><th>Serial</th><th>Team Name</th><th>Institution</th><th>Team Members</th><th>Team Max Rating</th></tr> </thead> <tbody> <tr><td rowspan=3>1</td><td rowspan=3>GodFathers Inc.</td><td rowspan=3>Shahjalal University of Science and Technology</td><td>[user:OweMeEternity,2026-05-11]</td><td rowspan=3>2229</td></tr><tr><td>[user:UshanGhosh,2026-05-11]</td></tr><tr><td>[user:AshrafSustS19,2026-05-11]</td></tr> <tr><td rowspan=3>2</td><td ...

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Milestones: ratings above 1500 and greatest falls (2024 edition) <i>Note.</i> This is an updated version of [this post](https://codeforces.me/blog/entry/104681). 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 (by absolute value) negative rating changes. The second one is the first users ever to reach some rating value. [cut] First table: <spoiler> <table> <tr> <th>Place</th> <th>&Delta;</th> <th>Person</th> </tr> ...

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First Ever Users to Reach Some Rating Milestones Revised: ratings above 1500 and greatest falls Several days ago I published a [table](https://codeforces.me/blog/entry/104320) with first people to reach certain ratings. It was a bit raw because, firstly, it was based on top 20000 Codeforces users by rating, and, secondly, because it only gave information about ratings divisible by 50. Now I have prepared a table that is of more complex design, but both issues are resolved. Good luck understanding what is going on in it. [cut] For several reasons I firstly put another table. This is the table of greatest rating falls 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 fall in ratings if you are high-rated. 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 right, but if someone finds it, you're welcome to pu...

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