Northern Eurasia Finals 2022 has concluded Two days ago Northern Eurasia Finals 2022 [took place](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Northern+Eurasia+Finals+2022&iso=20221207T1015&p1=352&ah=5), mirror of which was on Codeforces: [contest:1773]. In the next few hours the [standings](http://nerc.itmo.ru/archive/2022/standings.html) got unfrozen, thereby we know the list of the teams that qualified to the ICPC Finals this year: **1^st place 🏆** [MIPT](https://codeforces.me/ratings/organization/38): Yolki-palki ([user:Pechalka,2022-12-09], [user:Kapt,2022-12-09], [user:Tikhon228,2022-12-09]) **2^nd place 🥇** [HSE](https://codeforces.me/ratings/organization/250): FFTilted ([user:Kirill22,2022-12-09], [user:teraqqq,2022-12-09], [user:Ormlis,2022-12-09]) **3^rd place 🥇** [SPb SU](https://codeforces.me/ratings/organization/16): Urgant Team ([user:sava-cska,2022-12-09], [user:74TrAkToR,2022-12-09], [user:orz,2022-12-09]) **4^th place &#...

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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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Educational Codeforces Round 140 Editorial [problem:1767A] Idea: [user:BledDest,2022-12-17] <spoiler summary="Tutorial"> [tutorial:1767A] </spoiler> <spoiler summary="Solution (BledDest)"> ~~~~~ t = int(input()) for i in range(t): input() xs = [] ys = [] for j in range(3): x, y = map(int, input().split()) xs.append(x) ys.append(y) print('YES' if len(set(xs)) == 3 or len(set(ys)) == 3 else 'NO') ~~~~~ </spoiler> [problem:1767B] Idea: [user:BledDest,2022-12-17] <spoiler summary="Tutorial"> [tutorial:1767B] </spoiler> <spoiler summary="Solution (awoo)"> ~~~~~ for _ in range(int(input())): n = int(input()) a = list(map(int, input().split())) x = a[0] a = sorted(a[1:]) for y in a: if y > x: x += (y - x + 1) // 2 print(x) ~~~~~ </spoiler> [problem:1767C] Idea: [user:BledDest,2022-12-17] <spoiler summary="Tutorial"> [tutorial:1767C] </spoiler> <spoiler summary="Solution (BledDe...

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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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Educational Codeforces Round 113 [Rated for Div. 2] Hello Codeforces! On [contest_time:1569] [contest:1569] 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,2021-09-07] Dalabaev, Vladimir [user:vovuh,2021-09-07] Petrov, Ivan [user:BledDest,2021-09-07] Androsov, Mak...

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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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Educational Codeforces Round 28 Привет, Codeforces! [5 сентября в 18:05 по Москве](https://www.timeanddate.com/worldclock/fixedtime.html?day=5&month=9&year=2017&hour=18&min=5&sec=0&p1=166) начнётся Educational Codeforces Round 28. 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>. Раунд будет **нерейтинговый**. Соревнование будет проводиться по немного расширенным правилам ACM ICPC. После окончания раунда будет период времени длительностью в один день, 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 задач на 2 часа**. Мы надеемся, что вам они покажутся интересными. Задачи вместе со мной готовили Михаил [user:PikMike,201...

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Educational Codeforces Round 113 Editorial [problem:1569A] Idea: [user:BledDest,2021-09-09] <spoiler summary="Tutorial"> [tutorial:1569A] </spoiler> <spoiler summary="Solution (awoo)"> ~~~~~ for _ in range(int(input())): n = int(input()) s = input() for i in range(n - 1): if s[i] != s[i + 1]: print(i + 1, i + 2) break else: print(-1, -1) ~~~~~ </spoiler> [problem:1569B] Idea: [user:BledDest,2021-09-09] <spoiler summary="Tutorial"> [tutorial:1569B] </spoiler> <spoiler summary="Solution (Neon)"> ~~~~~ #include <bits/stdc++.h> using namespace std; int main() { ios_base::sync_with_stdio(false); cin.tie(NULL); int t; cin >> t; while (t--) { int n; string s; cin >> n >> s; vector<int> id; for (int i = 0; i < n; ++i) if (s[i] == '2') id.push_back(i); int k = id.size(); if (k == 1 || k == 2) { cout << "NO\n"; continue; } vector<string> t(n, string(n, '=')); for (int i = 0; i < n; ++i) t...

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Same code with Pypy3 and Python3 got different results on sgu-113 Today when I am trying to solve [acmsguru-113](https://codeforces.me/problemsets/acmsguru/problem/99999/113) with PyPy3 (because when I was submitting Python3, CodeForces noticed me that _"Almost always, if you send a solution on PyPy, it works much faster"_), I got lots of Wrong Answer on test 1. I thought it impossible because it's actually a very simple problem and I have confidence in my code. Then I rewrite it in C++, and with identical implementation it's accepted. Then I realized that there may be problems in input format, so I wrote a tokenizer to solve this problem. However, it's just another WA on 1. After one hour of struggling in finding bugs and differences, I found nothing but submitted it with Python3 &mdash; and it was an accepted! Here are the python code with tokenizer, and submissions with this code : (It's not allow to view others' submissions so I paste here) 63721667 Oct/29/2019 19:32UTC+8 Lily 113 &mdash; Nearly prime numbers Python 3 Accepted ...

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fread's behavior with line breaks UPD: I suppose that this is NOT the tests' fault. See https://codeforces.me/blog/entry/137318?#comment-1228025 . To be short, I think it goes like this: - `fread` reads all characters from the test, write them into the destination array. - `fread` looks for `"\r\n"`s (or just `"\r"`, idk), and remove `'\r'` from the array. Each of its occurence shifts the remaining part of the array to the left. - As a result, the final data gets shorter than the actual bytes it read from the file. However, it does not clear out the part after the shortened data. It returns the length of the shortened data, but if we check the data after it, we can see the leftovers. I can't find anything stating that `fread` is supposed to remove `'\r'`s from the reference, and it just feels really weird, but I guess this behavior's reason is explained at least. Searching further, I found that `stdin` is by default opened as text mode, and in that context `fread` can really truncate `'\r'`s to let users...

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[Tutorial] Range minimum query in O(1) with linear time construction <spoiler summary="TL; DR"> Build a sparse table over blocks of size $b = 30 \geq \log{n}$. Now we only need to answer queries of size smaller than $b$. For that, simulate a minqueue of size $b$ over the array, and store a mask of the elements that are currently active in the minqueue. Let $\text{mask[r]}$ be the minqueue mask when the simulation is at position $\text{r}$. Now we can see that, if $r-l+1 \leq b$, then `query(l, r) = r - most_significant_set_bit(mask[r] & ((1<<(r-l+1))-1))`. ~~~~~ template<typename T> struct rmq { vector<T> v; int n; static const int b = 30; vector<int> mask, t; int op(int x, int y) { return v[x] < v[y] ? x : y; } int msb(int x) { return __builtin_clz(1)-__builtin_clz(x); } int small(int r, int sz = b) { return r-msb(mask[r]&((1<<sz)-1)); } rmq(const vector<T>& v_) : v(v_), n(v.size()), mask(n), t(n) { for (int i = 0, at = 0; i < n; mask[i++] = at |= 1) { at = (at<<1)&((1<<b)-1); while (at and op(i, i-msb(at&-at)) == i) at ...

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UOJ Prime Round 2026 & UOJ Challenge #1 [UOJ Prime Round 2026](https://uoj.ac/contest/112) will be held at [10:00 AM on Saturday, August 8 (UTC +8)](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20260808T1000&p1=33)! The contest will last for 672 hours (28 days). [UOJ Challenge #1](https://uoj.ac/contest/113) will be held at [10:00 AM on Sunday, August 9 (UTC +8)](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20260809T1000&p1=33)! The contest will also last for 672 hours (28 days). UOJ Prime Round has already been mentioned in a [previous blog post](https://gezhiyuan.blog.uoj.ac/blog/9779). It will bring together problems from on-site contests over the past year that were solved by almost nobody during the contests and have received relatively few post-contest submissions. As for UOJ Challenge, [user:Gellyfish,2026-08-08] happened to have an interesting problem that did not seem to fit particularly well anywhere else, so we thought we might as well release it alongside UOJ Prime Round for eve...

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Ten years of competitive programming 2 Hey Codeforces! I’m AmirReza PourAkhavan, Codeforces Contest Coordinator. I let the story become complete and I’m sharing it now. The story is about a 16-year 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 post [here](https://codeforces.me/blog/entry/107465). 10th grade === Trying alone ------------------ In my tenth grade, the situation got worse. Before that, at least, I had some colleagues and at least a class per two weeks. But in the new grade, these brights disappeared too. Still, I was trying to do it alone. I remember when I learned the Dijkstra shortest-path algorithm and implemented it for the first time, how happy I was. Suddenly, my rating growth started. As you can see, my rating in Oct ‘14 was 1057 (minimum rating) and In Feb ‘15 I achieved 1761. Those years, >= ...

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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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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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Invitation to CodeChef Starters 113 (Rated for All) — 20th December We invite you to participate in CodeChef’s [Starters113](https://www.codechef.com/START113), this Wednesday, 20th December, rated for All. Time: [8:00 PM — 10:30 PM IST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=CodeChef+Starters+113&iso=20231220T20&p1=44&ah=2&am=30) Joining us on the problem setting panel are: - Setters: Satyam [user:satyam_343,2023-12-19] Kumar Roy. - Tester: Takuki [user:tabr,2023-12-19] Kurokawa. - Statement Verifier: Kanhaiya [user:notsoloud,2023-12-19] Mohan - Text Editorialists: Nishank [user:IceKnight1093,2023-12-19] Suresh. - Contest Admin : Satyam [user:satyam_343,2023-12-19] Kumar Roy. Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users. Also, if you have some original and engaging problem ideas, and you’re interested in them being used in Cod...

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AtCoder Regular Contest 113 Announcement We will hold AtCoder Regular Contest 113. - Contest URL: [https://atcoder.jp/contests/arc113](https://atcoder.jp/contests/arc113) - Start Time: [http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210221T2100&p1=248](http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210221T2100&p1=248) - Duration: 120 minutes - Number of Tasks: 6 - Writer: [user:degwer,2021-02-20], [user:maroonrk,2021-02-20] - Tester: [user:latte0119,2021-02-20], [user:reew2n,2021-02-20] - Rated range: &mdash; 2799 The point values will be 300-400-500-600-800-1000. We are looking forward to your participation!

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Codeforces Round #113 (Div. 2) Tutorial Initially the order of problems was A-C-E-D-B. But we were not sure about last two. [problem:166A] This is simple straight-forward problem --- you were asked to sort the teams with the following comparator: ($p_1 > p_2$) or ($p_1 = p_2$ and $t_1 < t_2$). After that you can split the teams into groups with equal results and find the group which shares the $k$-th place. Many coders for some reason used wrong comparator: they sorted teams with equal number of problems by descending of time. Such submits accidentally passed pretests but get WA #13. [problem:166B] Polygon A is convex, so it is sufficient to check only that every vertex of polygon B is strictly inside polygon A. In theory the simplest solution is building common convex hull of both polygons. You need to check that no vertex of polygon B belongs to this hull. But there is a tricky detail: if there are many points lying on the same side of convex hull than your convex hull must contain all these points as vertices....

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Active/Inactive status for CF users If you do not participate in rated rounds for 6 months you get status “Inactive”. Does it mean you are really inactive compared to others? What is a typical interval for users between their contests? I ran [my script ](https://github.com/NataIss/codeforces) on Oct 31 2021. It collected information about intervals between rounds for all users who have at least one interval, that means who has taken part in at least two rounds. It discovered 283412 appropriated users and counted 4552393 intervals. 95% of intervals are shorter than 113 days. Percentage of intervals shorter than 183 days is 97,09%. Mean value is 27,5 days, mediane is 7 days. Let’s look at the distribution of duration for intervals less or equal to 183.  So it is totally ok to mark users as inactive after a six-month absence. But I was just curious to find out somebody who came back after being inactive for a long time. What ...

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TOKI Open 2018 Post-Contest Hello! [TOKI Open 2018](http://codeforces.me/blog/entry/59182) has ended. Thank you to everyone who participated the contest. We decided to not consider any participants from the second window whose username is registered on the first window. We also decide to not consider any participants from the second window whose code is very similar to other user's code on the first window. After that, we consider a TOKI Open 2018 participant to be those who made at least one submission on either day. There were a total of 104 participants, which three of them get a fullscore. Congratulation to [user:1021839,2018-05-28], [user:Alex_2oo8,2018-05-28], and [user:zscoder,2018-05-28]. The full result of TOKI Open 2018 is available [here](https://docs.google.com/spreadsheets/d/1wH8FZGwYaDrMDsDaqTvvjMVUF5jmfriRligZgI16yL4/edit?usp=sharing). The skeletons, solutions, problem descriptions, and testcase generators for TOKI Open 2018 are available [here](https://github.com/jonathanirvings/toki...

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Codeforces Round #113 (Div. 2) Welcome dear friends) We are glad to introduce you regular Codeforces round #113 for Div.2 participants. Everyone can traditionally participate in it. Problems are prepared by known command of authors: Kholkin Pavel ([user:HolkinPV,2012-03-23]), Nikolay Kuznetsov ([user:NALP,2012-03-23]), Artem Rakhov ([user:RAD,2012-03-23]). Also thanks to Gerald Agapov ([user:Gerald,2012-03-23]) for his help, Michael Mirzayanov ([user:MikeMirzayanov,2012-03-23]) for Codeforces system and Mary Belova ([user:Delinur,2012-03-23]) for translating problems. **In todays contest would be one innovation. Score distribution would be dynamic. More information you can find [here](http://codeforces.me/blog/entry/4172))** We hope that todays round would be succesful. We wish you good luck and high rating! **UPD**: The contest is over. Hope you enjoy the problems) the editorial is already [here](http://codeforces.me/blog/entry/4173)) Congratulations to winners: 1. [user:Avalanche,2012-03-23...

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Codeforces Beta Round #86 Editorial <div><b>Div 2. Problem А.</b>&nbsp;<span class="Apple-style-span" style="font-family: verdana , arial , sans-serif;font-size: 13.0px;background-color: rgb(255,255,255);"><a href="http://codeforces.me/problemset/problem/114/A" style="color: rgb(0,0,204);">Cifera</a></span><br /></div><div>To solve this task, let's describe what is needed more formally. We should answer whether is number $l$ some positive degree of number $k$ or no. To answer this question we can proceed in 2 ways:<br />1) Using 64 bit data type, we can find minimal degree $h$ of number $k$, such that $k^h \ge l$. If $k^h = l$, then the answer is $YES$, and number of articles is equal to $h-1$. Otherwise, the answer is $NO$.<br />2) We will divide $l$ by $k$, until $k$ divides $l$ and $l \ne 1$. If $l = 1$, then the answer - $YES$ and number of articles is equal to $numberOfDivisions - 1$, and the answer is $NO$ otherwise.</div><div><br /></div><div><b>Div 2. Problem B.</b>&nbsp;<span class="Apple-style-span" sty...

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DIGIT DP Tutorial [ITERATIVE] #### Why iterative? I learned digit DP few years back but only recently I realised that the recursive solution is sometimes hard to debug and difficult to reason about. So this article aims to provide an iterative solution template that can be extended to solve similar problems. Problem Statement ------------------ Find count of numbers in range [L, R] such that sum of its digits is a prime number.<br> - $1 <= L,R <= 10^{18}$ Basic Idea ------------------ - A brute force approach would be to iterate through each number from L to R and check if sum of its digits is prime. This will obviously timeout as constraints are too large. - So which particular property can we count such that we don't consume too much time/memory? <br> Sum of digits of numbers! **Sum of digits of a number cannot exceed 180** for 18 digits, thus we will have to track only 180 states which will save time and memory.This is the key idea behind most digit DP problems: identify and track a proper...

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Educational Codeforces Round 41 [Rated for Div. 2] Hello Codeforces! On [April 04, 17:05 MSK](https://www.timeanddate.com/worldclock/fixedtime.html?day=4&month=4&year=2018&hour=17&min=5&sec=0&p1=166) Educational Codeforces Round 41 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 Div. 2**. It will be held on extented ACM ICPC rules. After the end of the contest you will have one day to hack any solution you want. You will have access to copy any solution and test it locally. You will be given **7 problems** and **2 hours** to solve them. The problems were prepared by Roman [user:Ajosteen,2018-04-03] Glazov, Adilbek [user:adedalic,2018-04-03] Dalabaev and me. We'd like to thank Mikhail [user:PikMike,2018-04-03] Piklaye...

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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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Codeforces Round #521 (Div. 3) I am so sorry about very long gaps between the contests but I really don't have enough time to prepare the problems. So... &lt;copy-pasted-part&gt; Hello! [contest:1077] will start at [contest_time:1077]. 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 solv...

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Problems that I authored so far Hi everyone! I wanted to write such a blog for a long time. I finally decided to do it after Codeforces Round $934$. I would like to thank [user:Non-origination,2024-03-21], [user:GoatTamer,2024-03-21] and [user:KingRayuga,2024-03-21] for discussing the problems with me. For each problem, I tried to include the some interesting stuff if I could remember. I tried to avoid using spoilers for the problems. So you can look at the comments even if you have not tried the problem. | # | Date | Problem | Difficulty | Contest | Comment |----|-----------|---------------------------------|------------|--------------------------------------|--------------------------------------| | 1 | Aug 2021 | [Tree Distance Sum](https://www.codechef.com/problems/TREEDIST) | Div 2 E | Codechef Starters 10 | My first problem which appeared in some contest. I noticed some nice properties about the dfs traversal and de...

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Topcoder Marathon Match 113 **[Topcoder MM 113](https://www.topcoder.com/challenges/30110632)** is scheduled to start at [21:00 UTC -5 on Dec 16, 2019](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Marathon+Match+113&iso=20191216T21&p1=3919). **[Register Now!](https://www.topcoder.com/challenges/30110632)** **TCO20 Eligible**: Competing in Marathons can help you qualify for TCO20 Marathon Tournament Finals. [Learn More](https://tco20.topcoder.com/competition-overview/marathon). **How to compete?** In order to compete in a Topcoder Marathon Match, you will need to click the Register button next to the appropriate Marathon Match within the Active Contests list and agree to the rules of the event. **Want to Practice?** To understand what kind of problems do Marathon Matches have and to get the feel of a Topcoder Marathon Match you can visit the [practice rooms](https://community.topcoder.com/longcontest/?module=ViewPractice) and participate in the Marathon Matches previously hosted on Topcode...

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Codeforces Round #286 Editorial (Complete) **Edit (Jan 22, 2:45 AM UTC):** Added Div1E and the editorial is now complete. I am sorry for the delay. **Edit (Jan 21, 9:45 AM UTC):** Added the explanation for Div1C/2E, and the problem setters' codes. Div1E will need several more hours. Thank you again for your patience. First, here are some statistics on this round: <table> <tr> <td>Division</td> <td>Registrants</td> <td>Participants</td> <td>A Accepted</td> <td>B Accepted</td> <td>C Accepted</td> <td>D Accepted</td> <td>E Accepted</td> </tr> <tr> <td>1</td> <td>1364</td> <td>572 (*)</td> <td>294</td> <td>199</td> <td>8</td> <td>113</td> <td>1</td> </tr> <tr> <td colspan="3">(Estimated number of AC by me)</td> <td>800 (wrong)</td> <td>500 (wrong)</td> <td>70 (FAIL)</td> <td>90 (ok)</td> <td>5 (wrong)</td> </tr> <tr> <td>2</td> <td>4016</td> <td>2028</td> <td>1355</td> <t...

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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 IPSC 2014 Badum badum... The Internet Problem Solving Contest takes place again in 2014! The registration's started (those of you who competed last year should've gotten an e-mail about it) and will be open until the end of the contest. The contest will take place from <s>15.6.2014 10:00 UTC</s> [15.6.2014 11:00 UTC](http://www.timeanddate.com/worldclock/fixedtime.html?month=6&day=15&year=2014&hour=11&min=0&sec=0) to <s>15.6.2014 15:00 UTC</s> [15.6.2014 16:00 UTC](http://www.timeanddate.com/worldclock/fixedtime.html?month=6&day=15&year=2014&hour=16&min=0&sec=0) and will be preceded by a short practice session. You can find the registration form, archive and everything at [the contest site](http://ipsc.ksp.sk/2014/). The rules can be found at the contest site or in [my blog post about last year's IPSC](http://codeforces.me/blog/entry/7797). That's why this post is short &mdash; you can just read that one and replace the dates. Also, if you think one blog post isn't a good enough ...

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Hack me! (Bayan 2015 Contest Warm Up) Welcome in [contest:475] hacks description. This round was pretty good for hackers, but again there were nearly two times more unused opportunities for hack than the used ones. Let's look at them. If you want to share your hack (or mistake) -- we're waiting for your comments. 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:475A] </small> | 243 (53.06%) | 205 (44.76%)| 10 (2.18%) | 458 | 349 (15.73%) | 1869 (84.27%) | 2218 | <small> [problem:475B] </small> | 94 (50.81%) | 72 (38.92%)| 19 (10.27%) | 185 | 192 (10.35%) | 1663 (89.65%) | 1855 | <small> [problem:475C] </small> | 6 (14.63%) | 26 (63.41%)| 9 (21.95%) | 41 | 113 (25.80%) | 325 (74.20%)...

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Some Statistics About CF Rating Changes (2018/07 update) #### Overview There are 1409603 rating changes in 792 rated contests (by 2018/07/14, including those mentioned in the "Something Weird" section). There are 142117 users with at least one rating change. The overall average of deltas is -6.671139. #### Rating Changes Distribution <img src="https://image.ibb.co/gZjnpJ/hist.png" width="90%"/> <img src="https://image.ibb.co/jejnpJ/hist2.png" width="90%"/> (Well, it looks like a boa constrictor eating an elephant...) #### Top 20 Events: Positive Rating Change <table> <tr> <th>#</th> <th>Who</th> <th>Δ</th> <th>Rating</th> <th style="width: 25em;">Contest</th> </tr> <tr> <td>1</td> <td>[user:Mhammad1,2018-07-16]</td> <td><span style="color:green;font-weight:bold;">+803</span></td> <td><span style="font-weight:bold;" class="user-gray">-22</span> → <span style="font-weight:bold;" class="user-gray">781</span></td> <td>[contest:814]</td> </tr> <tr> <td>2</td> <td>[user:white_1,2018-07-16]</td> <td><span style=...

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CEOI Results Here are the results for Central-European Olympiad in Informatics. Congratulations to winners! 1 Eduard Batmendijn Slovakia 355 2 Andrei Heidelbacher Romania 339 3 Ivan Lazarić Croatia 312 4 Jarosław Kwiecień Poland 282 5 Domagoj Bradač Croatia 249 6 Michał Zieliński Poland 246 7 Mihai Popa Romania 240 8 Martin Hora Czech Republic 238 9 Dominik Gleich Croatia 225 9 Mislav Bradač Croatia 225 11 Silviu-Emil Popescu Romania 208 12 Szilveszter Székely Hungary 202 13 Vendel Nagy Hungary 192 14 Barbora Kováčova Slovakia 188 15 Žiga Željko Slovenia 183 16 Eugenie-Daniel Posdărăscu Romania 179 17 Tonko Sabolčec Croatia 177 18 Benjamin Schmid Switzerland 176...

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An amazing way to calculate 10^18-th fibonacci number using 25 lines of code. Based on the approach in [my previous blog](http://codeforces.me/blog/entry/14385), today, I found an amazing way to calculate large fibonacci numbers (in some modulo). According to part IV of my previous blog, let $f(n)$ be the $(n+1)^th$ fibonacci number, we have two case: $n$ is even and $n$ is odd. - $f(2*k) = f(k)*f(k) + f(k-1) * f(k-1)$ - $f(2*k+1) = f(k)*f(k+1) + f(k-1)*f(k)$ There are only at most $O(4*\log n)$ states. I don't like to prove this, but I can ensure it is true by doing some following experiment. Let's divide n into groups by depth, you will realize a special property: Each depths only contains at most 4 values of n. call f(1000): ~~~~~ Depth[0] : 1000 Depth[1] : 499 500 Depth[2] : 248 249 250 Depth[3] : 123 124 125 Depth[4] : 60 61 62 63 Depth[5] : 29 30 31 32 Depth[6] : 13 14 15 16 Depth[7] : 5 6 7 8 Depth[8] : 1 2 3 4 Depth[9] : 0 1 2 Depth[10] : 0 1 ~~~~~ call f(123123123122): ~~~~~ Depth[0] : 123123123122 Dep...

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Sieve of Eratosthenes It is easy to find if some number (say N) is prime or not &mdash; you simply need to check if at least one number from numbers lower or equal sqrt(n) is divisor of N. [cut] This can be achieved by simple code: ~~~~~ boolean isPrime( int n ) { if ( n == 1 ) return false; // by definition, 1 is not prime number if ( n == 2 ) return true; // the only one even prime for ( int i = 2; i * i <= n; ++i ) if ( n%i == 0 ) return false; return true; } ~~~~~ So it takes sqrt(n) steps to check this. Of course you do not need to check all even numbers, so it can be "optimized" a bit: ~~~~~ boolean isPrime( int n ) { if ( n == 1 ) return false; // by definition, 1 is not prime number if ( n == 2 ) return true; // the only one even prime if ( n%2 == 0 ) return false; // check if is even for ( int i = 3; i * i <= n; i += 2 ) // for each odd number if ( n%i == 0 ) return false; return true; } ~~~~~ So let say that it take...

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Codeforces Global Rounds 2020: Final Results In 2020, with the support of XTX Markets, 6 rounds of the Codeforces Global Rounds were held. Each round was common for both divisions. All such rounds were rated for all participants. At each such round, 50 brand T-shirts were handed out, and we gave T-shirts to all problem writers! I say a big thank you to XTX Markets (and personally to Yuri Bedny and Alexander Gerko) for supporting Global Rounds. Without your help, we could not host them! I sincerely admire companies like these who come to support and develop the community that some of their employees come from. It will be great if other companies follow the example and also offer their help. We need it! The prizes for the 6-round series in 2020: - In each round, top-100 participants get points according to the [table](https://pastebin.com/QT5sXEaT). - The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest. - The best 20 participants over all series get...

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Intuition behind the solution to UVa 11396 Hi, Today, I worked on the following problem: [https://onlinejudge.org/external/113/11396.pdf](https://onlinejudge.org/external/113/11396.pdf) (UVa 11396) While I recognized that the problem involved bipartite graphs, I could not figure out how to solve the problem, so I looked at the answer. Accordingly, I found out that a graph $G$ can be decomposed into $K_{1, 3}$ graphs if $G$ is bipartite. While this solves the problem, I'm not so sure why this is true. I understand that each of the $K_{1, 3}$ graphs can have their center vertex colored black leaving the remaining three vertices to be colored white; however, I can't really figure out where the "each vertex has degree $3$," and "decomposition" (the graph can have many $K_{1, 3}$'s in them) parts come into play. I've tried drawing pictures, but I can't seem to get the intuition that a bipartite graph check is enough. It's also pretty hard for me to come up with examples in which the criteria are satisfied and a decompo...

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Notes on Codeforces Beta Round #113, Div2- A, C, D, E [problem:166A] Sort the array in the required order, and find out all the terms that have exactly the same data as the $k$-th one. [problem:166C] In fact, we can keep inserting $x$ into the array until we find that the median is equal to $x$. Why this works? One can see that if the median is less than $x$, then we should insert more integers that are larger than $x$; otherwise we should insert more integers that are less than $x$. Nevertheless, $x$ can be viewed as an integer that is both “less than” and “larger than” $x$ itself. It can be proved that it is definitely sufficient to insert at most $n+1$ $x$s, and thus the complexity is $N^{2}log(N)$. [problem:166D] My codes have about 400 lines.... The basic idea is dp. We use $dp[i][j]$ to denote the maximum profit we can obtain, when the $j$-th customer has made his decision (all the customers are sorted in an increasing order of their feet sizes $l$). In details, $i$ can take values $0, 1, 2, 3$, which is...

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Итоги Украины на IOI 2013 Вот и подошло к концу IOI 2013. Результаты Украины не так хороши как хотелось бы, но все же ни один украинец не приедет домой без медали. С этим я поздравляю наших ребят! Первый тур был более-менее неплохой для нас! Роман Фурко ([user:Furko,2013-07-10]) довольно неплохо выступил и взял на первом туре 233 балла, что позволило ему приблизится к "Золоту". Роман Рубаненко ([user:Rubanenko,2013-07-10]) набрав 167 баллов уверенно держался в "серебре". Илья Шевченко ([user:Scorpy,2013-07-10]) с немалым риском, за несколько минут до конца добил первую задачу на 100 баллов, тем самым обеспечив себе после первого тура место в "бронзе", но довольно близко к "серебру". Дмитрий Федоряка ([user:fedimser,2013-07-10]) же показал всю свою силу во втором туре! Набрав 190 баллов(максимальный результат Украины во втором туре), тем самым обеспечив себе место в "бронзе". К сожалению второй тур для большинства участников Украины был не очень удачным, и это понизило их позици...

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Mail.Ru Cup 2018 — Results of R1+R2+R3 Here are merged results of [contest:1054], [contest:1055] and [contest:1056] according to the GP100 scores (see the announcement for the details https://codeforces.me/blog/entry/62355). Best two contests give the summary score of a participant. This table is unofficial yet. But anyway... congratulations to the winnerzzzz! | Place | Contestant | = | Round 1 | Round 2 | Round 3| | - | - | - | - | - |-| | 1 | [user:mnbvmar,2018-11-25] | 1497 | 1000 | 497 | 29 | | 2 | [user:V--o_o--V,2018-11-25] | 1281 | 575 | 575 | 706 | | 3 | [user:Radewoosh,2018-11-25] | 1265 | &mdash; | 265 | 1000 | | 4 | [user:aid,2018-11-25] | 1204 | 204 | 1000 | 142 | | 5 | [user:LHiC,2018-11-25] | 1203 | 497 | 706 | 226 | | 6 | [user:Um_nik,2018-11-25] | 997 | 706 | 291 | 235 | | 7 | [user:ksun48,2018-11-25] | 788 | 291 | &mdash; | 497 | | 8 | [user:SpyCheese,2018-11-25] | 742 | 371 | 371 | 265 | | 9 | [user:RAVEman,2018-11-25] | 619 | 19 | 176 | 443 | | 10 | [user:scott_wu,2018-11-25] | 614...

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Codeforces Global Rounds 2021: Final Results (GR13-GR18) Tomorrow will be the first global round of this year. And we are happy to sum up the results of last season. We announce the results! We remind you that the global rounds are a joint initiative of XTX and Codeforces. We are happy to announce that they continue into the new year. 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. The final standings after six rounds (sorted by total points in four best placed rounds): | Place | Contestant | = | GR 13 | GR 14 | GR 15 | GR 16 | GR 17 | GR 18| |--...

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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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Codeforces Global Rounds 2021: Current Results (GR13-GR17) In 2021 (as in 2019 and 2020), with the support of XTX Markets, 6 rounds of the new Codeforces Global Rounds are held: common rounds for both divisions of 7–9 problems each. The duration of the rounds is 2-3 hours, depending on the number and complexity of the problems. All such rounds are rated for all participants. <i>At each such round, 50 brand T-shirts are handed out, and we are happy to give T-shirts to all problem authors.</i> The prizes for the 6-round series in 2021: - 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 five rounds he placed the highest. - The best 20 participants over all series get sweatshirts and place certificates. Current standings after five rounds (sorted by total points in four best placed rounds): | Place | Contestant | = | GR 13 | GR 14 | GR 15 | GR 16 | GR 17| | - | - | - | - | - | - | - | - | | ...

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

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Counterexample to IOI Sphinx model code So I was trying to upsolve IOI 2024 Q6 Sphinx. In the editorial phase 2 states to split the condensed graph into two sets, and perform binary search on these sets for every colour, to determine which components have what colour. However, each binary search needs $\log N\approx8$ queries to perform the actual binary search, along with an additional query to "confirm" that no other component in the set has that colour. Along with the rest of the solution, this gives a query count of $3N+a+N\log N$, where $a$ is the number of monochromatic components. This means that, in the worst case, the solution would take $4N+N\log N$, which is up to $3000$ queries, more than is allowed in the problem. At first, I thought that there would be some amortisation which keeps the query count under the limit of $2750$ queries, but then I made the following construction: Consider the test case with $N=250$ vertices, all with different colours. Then, the graph is constructed by taking the first 248 vertic...

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Mail.Ru Cup 2018 — Results of R1+R2 Here are merged results of [contest:1054] and [contest:1055] according to the GP100 scores (see the announcement for the details https://codeforces.me/blog/entry/62355). | Place | Contestant | = | Round 1 | Round 2| | - | - | - | - | - | | 1 | [user:mnbvmar,2018-11-10] | 1497 | 1000 | 497 | | 2 | [user:aid,2018-11-10] | 1204 | 204 | 1000 | | 3 | [user:LHiC,2018-11-10] | 1203 | 497 | 706 | | 4 | [user:V--o_o--V,2018-11-10] | 1150 | 575 | 575 | | 5 | [user:Um_nik,2018-11-10] | 997 | 706 | 291 | | 6 | [user:SpyCheese,2018-11-10] | 742 | 371 | 371 | | 7 | [user:scott_wu,2018-11-10] | 614 | 307 | 307 | | 8 | [user:BudAlNik,2018-11-10] | 531 | 277 | 254 | | 9 | [user:tourist,2018-11-10] | 443 | &mdash; | 443 | | 9 | [user:lewin,2018-11-10] | 443 | 443 | &mdash; | | 11 | [user:Golovanov399,2018-11-10] | 403 | &mdash; | 403 | | 11 | [user:Endagorion,2018-11-10] | 403 | 403 | &mdash; | | 13 | [user:j_______________________,2018-11-10] | 384 | 198 | 186 | | 14 | [...

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Google CodeJam World Finals <p>Google CodeJam World Final will be conducted on July 29th at&nbsp;<a href="http://timeanddate.com/worldclock/fixedtime.html?iso=20110729T09&amp;p1=248&amp;ah=4">9:00</a>&nbsp;AM Tokyo time</p><div><a href="http://apps.topcoder.com/forums/?module=Thread&amp;threadID=706558&amp;start=50&amp;mc=113#1387375">Participants</a></div><div><a href="http://code.google.com/codejam">Website</a></div><p></p>

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Codeforces Round #268 [contest:468] and [contest:469] round statistics [cut] : ### Div. 1 #### First accepted: **A** (00:03) [user:135678942570,2014-09-19] <br/> **B** (00:19) [user:KADR,2014-09-19] <br/> **C** (00:25) [user:asi1024,2014-09-19] <br/> **D** (01:42) [user:ecnerwal,2014-09-19] <br/> #### Total hack attempts: +241:-213 #### Top-5 hackers: **950** [user:PavelKunyavskiy,2014-09-19] +10:-1 <br/> **850** [user:RAVEman,2014-09-19] +10:-3 <br/> **800** [user:Merlininice,2014-09-19] +9:-2 <br/> **700** [user:wjh720,2014-09-19] +9:-4 <br/> **600** [user:Balajiganapathi,2014-09-19] +6:-0 <br/> #### Other info <br/> [Complete Results](https://lh5.googleusercontent.com/-5zjVAw0DWaU/VB3kYuQh1vI/AAAAAAAACT0/hOok89lJwcg/s0/CF_268_1_2.png)<br/><br/> <br/><br/> ![ ](https://l...

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Codeforces Global Rounds 2020: Current Results (GR7-GR10) In 2020 (as 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 problem authors and problem testers.</i> The prizes for the 6-round series in 2020: - In each round top-100 participants get points according to the [table](https://pastebin.com/QT5sXEaT). - The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest. - The best 20 participants over all series get sweatshirts and place certificates. Current standings after four rounds (sorted by total points in four rounds): | Place | Contestant | = | GR 7 | GR 8 | GR 9 | GR 10| |--|--|--|--|--...

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Who participated most? **UPD:** The calculation updated, for some reason I filtered only CF style competitions. Now it includes everything. Still [user:ruban,2024-08-07] best :) I revisited some data from Codeforces and, [after 5 years](https://codeforces.me/blog/entry/72410), decided to calculate again who has participated in the most contests. I took into account all official contest participations, including those where a user participated unofficially. However, I excluded Practice/Virtual contests. P.S: I think no one will beat [user:ruban,2024-08-07] ever :) |Rank|Handle|Total|Official|Unofficial| |---|---|---|---|---| | 1 |  [user:ruban,2024-08-13] | 1164 | 1090 | 74 | | 2 |  [user:kmjp,2024-08-13] | 972 | 547 | 425 | | 3 |  [user:dreamoon_love_AA,2024-08-13] | 891 | 538 | 353 | | 4 | ![ ](https://codeforces.com/codeforces.org/s...

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Codeforces Global Rounds 2020: Current Results (GR7-GR9) In 2020 (as 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 problem authors and problem testers.</i> The prizes for the 6-round series in 2020: - In each round top-100 participants get points according to the [table](https://pastebin.com/QT5sXEaT). - The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest. - The best 20 participants over all series get sweatshirts and place certificates. Current standings after three rounds (sorted by total points in three rounds): | Place | Contestant | = | GR 7 | GR 8 | GR 9| |--|--|--|--|--|--| ...

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Республиканская олимпиада 2026 года. Казахcтан. Результаты. <spoiler summary="Результаты прошлых лет"> [2025](https://codeforces.me/blog/entry/140577) [2024](https://codeforces.me/blog/entry/127605) [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** | **Место** | **ФИО** | **CF handle** | **1 тур** | **2 тур** | **Общий** | **Медаль** | |---|---|---| | 1 | Бауыржан Шөкей | [user:Shad_29, 2025-08-27] | 234 | 143 | 377 |  | | 2 | Алишер Еламан | [user:Alish_1_2100,2026-03-22] | 203 | 135 | 338 | ![ ](https://codef...

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Pi approximation day I was somewhat surprised to learn that besides [Pi Day](http://en.wikipedia.org/wiki/Pi_Day) celebrated on the 14-th of March we have [Pi Approximation Day](http://en.wikipedia.org/wiki/Pi_Approximation_Day) celebrated today, on the 22-th of July. *Don't be surprised, both link lead to the same page.* I'm curious, whether it is possible to invent the day for another well-known approximation `355 / 113`? Well... It could be the `113-th` minute of the `355-th` day of the year &mdash; something closer to astronomic time notation...

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Betlista's TopCoder SRM 648 editorial In SRM there were 1303 registered participants [cut] - DIV1 562, DIV2 628 + 113 newcomers ### DIV2 — easy (250) Ona have to return the length of binary number T/K without the zeros at the beginning. ### DIV2 — medium (500) Greedy &mdash; check, whether after pair removal, the number of components is increased, if so, remove the pair. Return the number of such pairs. ### DIV2 — hard (1000) Inspired by hippie (room 61). DP: We can calculate for each AC, BC and CC (A count, B count, ...) and PC (Pair Count), whether it is possible or not. Once we know it is possible, we can run the same algorithm, to find the string. ### DIV1 — easy (250) Same as DIV2 hard, but with only two characters instaed of three. **Note:** as always I will write more detailed descripton a little later...

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Help in this Counting Problem. Was asked in one of the FAANG OA. ~~~~~ Given a string **S** consisting of digits [0-9], count the number of ways this string can be split into continuous substrings such that each substring is a prime number. Each digit must be in one substring and the entire string must be used. **Note:** The input string does not contain leading zeros. Each number split of the given number must be in the range `2 to 1e6` inclusive. Since the answer can be large, return the answer modulo `1e9+7`. **Constraints** 1 <= | S | <= 1e5 **Example** _input_ 11373 _output_ 6 _Explanation_ [11, 3, 7, 3], [11, 3, 73], [11, 37, 3], [113, 7, 3], [113, 73], [11, 373]. Can anyone help me out? Thanks in advance. Happy Coding... P.S.: This is my first blog, so correct me if I'm wrong anywhere. ~~~~~ `Feel free to share your approach.`

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Codeforces Global Rounds 2019: Current Results 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 two rounds: | Place | Contestant | = | Round 1 | Round 2| | - | - | - | - | - | | 1 | [user:tourist,2019-06-01] | 1706 | 1000 | 706 | | 2 | [us...

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Problems that I authored so far **UPD 1 [May 17 2025]:** I added my problems from Ukrainian Olympiad in Informatics (among others). They are available here: [contest:105820] Hi everyone! I wanted to write such a blog for a long time, motivated by similar blogs [by](https://codeforces.me/blog/entry/108940) [user:adamant,2023-02-20] and [by](https://codeforces.me/blog/entry/108595) [user:tibinyte,2023-02-20]; I finally decided to do it after my Universal Cup contest. This is not a super-comprehensive list, I also set some problems for some local contests, but that's most of it. I want to encourage other setters to write such blogs. For me, it's very interesting to read about the backstories of some problems and also to see all the problems by some author gathered in one place (as most authors give problems to several platforms). One important point. As you will see from the comments, many of my problems were improved by other people, and I myself improved some problems by other people. I think that it's cruc...

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Help needed in Atcoder ABC-113 D I was trying to solve [this](https://abc113.contest.atcoder.jp/tasks/abc113_d) problem form recent Atcoder's beginner contest , but after scratching my head for almost 2h I could not come up with the solution.Then I tried to look for the editorials but this time they were not in English. [user:square1001,2018-12-01] has provided solution there which I find uses some kind of DP. Can anyone who has solved this problem explain DP recurrence behind this ?

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Country statistics Hi guys! I have prepared for you some statistics on how countries are performing against each other in Codeforces which I hope you will find interesting! ## Top 5 countries with the most users with certain rank:  ## Top 5 countries with highest percentage of their users in a certain rank: (Here I don't count countries that have less than 10 Codeforces users)  #### Newbie:  #### Pupil:  #### Specialist:  #### Expert:  #### Candidate Master:  #### Master: ![ ](/pre...

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Well... There goes my streak As you all know, codeforces was down for like 7 hours yesterday, and these 7 hours should have been the time when I did some CP, and obviously I couldn't. So these goes my streak of 113 days :( btw my timezone is EST so it's normal if you see less than 113 days

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"Итоги года — 2015" — результаты. Всего во втором туре "Итогов года &mdash; 2015" проголосовало 128 участников. Это является рекордным результатом за всё время проведения конкурсов "Итоги года". [Результаты голосования](http://snarknews.info/vote2016.html) Поздравляем победителей! Награждение будет проведено во время зимних сборов в Петрозаводске, которые пройдут с 29 января по 8 февраля. Точная дата награждения будет опубликована позднее. Немного статистики. Сумма поданных голосов по номинациям: участник года &mdash; 123 голоса, команда года &mdash; 124 голоса, дебют года &mdash; 118 голосов, прогресс года &mdash; 121 голос, онсайт года &mdash; 117 голосов, публикация года &mdash; 100 голосов, проект года &mdash; 113 голосов, событие года &mdash; 117 голосов, персона года &mdash; 114 голосов. Таким образом, наибольшее число участников проголосовало за команду года, наименьшее (причём с отрывом в 13 голосов от предпоследнего места) &mdash; за публикацию года.

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$O(N^2)$ solution to Facebook Hacker Cup 2021 Round 1 problem A2 (part one) Right after the end of Facebook Hacker Cup 2021 Round 1, [user:wjomlex,2021-09-25] posted the following [comment](https://codeforces.me/blog/entry/94726?#comment-839269) in the discussion section under the announcement blog: > A common issue was people writing O(N^2) solutions to problem A when O(N) solutions are necessary. You won't be able to run an O(N^2) solution in 6 minutes when N = 800,000. But is this really true? Challenge accepted! ##### Problem A1 <div> <spoiler summary="Spoiler"> First of all, here is an $O(N)$ solution for [problem A1](https://www.facebook.com/codingcompetitions/hacker-cup/2021/round-1/problems/A1): <spoiler summary="Spoiler"> ~~~~~ #include <iostream> #include <vector> #include <stdint.h> using namespace std; /* * This is a solution for problem A1. Time complexity: O(N) * Characters in the input buffer are remapped: 'F' => 0, 'X' => 1, 'O' => 2 */ static int32_t solve_a1(const int8_t *arr, int n) { int32_t ans = 0, h...

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Как то раз в 113. Как то раз, в 113 я забыл выйти из Сюдедорсеса. Это уже второй раз для меня, и по этому это в двойне пичально(. Традиционно я прошу себе плюсиков), в надежде что вы проминусуете.

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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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Codeforces Global Rounds 2019: Final Results In 2019, with the support of XTX Markets, 6 rounds of the new Codeforces Global Rounds were held. Each round was common for both divisions and had 7–9 problems. The duration of the rounds was 2-3 hours, depending on the number and complexity of the problems. All such rounds were rated for all participants. At each such round, 50 brand T-shirts were handed out, and we gave T-shirts to all authors and problem testers as well. 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. Final results: [cut]<br/> | Place | Contestant | = | Round 1 | Round 2| Round 3 | Round 4 | Round 5 | Round 6 | | - | - | - | - | - | - | - | - | - | | 1 | [user:tourist,2019-12-17] | <b> 2987 </b> | ...

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Help needed for UVA 11312 — Flipping Frustration Problem Link: https://uva.onlinejudge.org/external/113/11312.pdf My partial solution: 1) If the given values do not satisfy this equation -> rx + ly = t then there is no solution. 2) Now, in order to find the minimum value I can do a BFS but this will result me a TLE in certain cases. How should I implement this part cleverly?

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Статистика использования языков программирования на РОИ с 1997 года **Обновление 6 ноября 2019 года:** Добавлены данные за 2019 год. Полностью исчез Паскаль. Совсем. Ни одного сданного решения. **Обновление 22 апреля 2018 года:** Добавлены данные за 2018 год. Принципиально ничего не меняется, очень сильно выросла доля участников, которые пишут и на C++, и на Python. 3/4 участников пишет только на C++, но почти 1/5 участников пишет на С++ и на Python. **Обновление 1 апреля 2017 года:** Добавлены данные за 2017 год. Предсказуемо сокращается число участников, пишущих на Pascal, но неожиданно сократилось и число участников, использующих Java. Python по-прежнему остается распространенным вторым языком после C++. **Обновление 9 апреля 2016 года:** Добавлены данные за 2016 год. По-прежнему, для каждого участника считается язык, который он преимущественно использовал. Число в скобках&nbsp;&mdash; количество людей, которые сдали хотя бы одно решение на этом языке. То есть достаточно мало участников пишет только на Python или преимущественно на Pyth...

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Республиканская олимпиада 2021 года. Казахcтан. Результаты. 2021 : https://codeforces.me/blog/entry/90111 2020 : https://codeforces.me/blog/entry/80808 2019 : https://respa.daryn.kz/ 2018 : https://codeforces.me/blog/entry/58432 2017: https://codeforces.me/blog/entry/51416 ####9 Класс <html> <body> <style type="text/css"> .tg {border-collapse:collapse;border-spacing:0;} .tg td{border-color:black;border-style:solid;border-width:1px;font-family:Arial, sans-serif;font-size:14px; overflow:hidden;padding:10px 5px;word-break:normal;} .tg th{border-color:black;border-style:solid;border-width:1px;font-family:Arial, sans-serif;font-size:14px; font-weight:normal;overflow:hidden;padding:10px 5px;word-break:normal;} .tg .tg-0pky{border-color:inherit;text-align:left;vertical-align:top} </style> <table class="tg" style="undefined;table-layout: fixed; width: 579px"> <colgroup> <col style="width: 50px"> <col style="width: 160px"> <col style="width: 170px"> <col style="width: 97px"> <col style="width: 102px"> </colgroup...

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Codeforces rating distribution over time I was curious about rating inflation, so I generated a json object containing counts and percentiles and some plots of codeforces rating distribution over months, only counting active contestants: <spoiler summary="Json object"> ``` { "2015-01-01": { "Active": { "count": 21827, "percentile": 0.0 }, "Expert+": { "count": 6763, "percentile": 69.01543959316443 }, "CM+": { "count": 1778, "percentile": 91.85412562422688 }, "M+": { "count": 724, "percentile": 96.68300728455583 }, "IM+": { "count": 236, "percentile": 98.91877033032483 }, "GM+": { "count": 124, "percentile": 99.43189627525541 }, "IGM+": { "count": 21, "percentile": 99.90378888532551 }, "LGM": { ...

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Teams for ACM ICPC World Finals 2015 — Marrakesh, Morocco I'm planning to make a scoreboard for the ACM ICPC World Finals 2015, the scoreboard will contain the TopCoder and Codeforces handles for the contestants. It will be similar to [this one](http://a2oj.com/ICPC.jsp) (but with some more improvements). Please post the Codeforces handles for the qualified teams here. I'll keep updating this post once I get any new information. Any suggestions for the scoreboard are welcome for sure. I'll add all the handles I get in the following table: | | Country | University | Contestant 1 | Contestant 2 | Contestant 3 | |:--:|:--:|:--:|:--:|:--:|:--:| | 1 | Russia | St. Petersburg National Research University of IT, Mechanics and Optics | [user:tourist,2015-05-19] | [user:qwerty787788,2015-05-19] | [user:VArtem,2015-05-19] | | 2 | Japan | The University of Tokyo | [user:rng_58,2015-05-19] | [user:semiexp,2015-05-19] | [user:wrong,2015-05-19] | | 3 | China | Shanghai Jiao Tong University | [user:AngryBacon,2015-05-19] | [user:rowdark,201...

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Республиканская олимпиада 2022 год. Казахстан 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://codeforces.me/blog/entry/58432 2017 : https://codeforces.me/blog/entry/51416 #### 9 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>Таймас Мансур</td><td>[user:gamicrab,2022-04-19]</td><td>322</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>Абжами Ерсултан</td><td>[user:syrtin,2022-04-19]</td><td>274</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>Шермаханов Ильяс</td><td>[user:Tenjin,2...

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