Interesting situation about a counting problem: Solved the problem, I don't know how The first stage of the National Olympiad in Informatics in Romania is taking place this Saturday, so this week there were hosted some practice contests on the Romanian OJ [**kilonova**](https://kilonova.ro/). I participated in one of them and one of the problems basically sounds like this: "You are given **3** numbers $A,B,C(A,B,C \le 3000)$, count the number of strings that have $A$ letters `a` in them, $B$ letters `b` and $C$ letters `c` and also don't have `abc` as a substring". As I have some skill issue when it comes to combinatorics and dynamic programming, I did not manage to solve the problem for a full score but, my interest for this problem came back to life while talking to [user:Matteo.Verz,2023-03-16], who told me that he managed to solve the problem (we both tested and his solution gets a full score) in linear time. I was quite surprised because the constraints allowed solutions with a quadratic time complexity and all of the solutions that I heard about were also...

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Info1Cup 2025 The 2025 edition of the first international junior Olympiad of the year, [Info1Cup](https://www.info1cup.com) is starting today with its competition days taking place tomorrow and on Sunday, so let's use this blog to talk about the contest days and their problems after the contest days are over. You can also write the Codeforces handles of the [participants](https://www.info1cup.com/participants) and maybe even predict potential winners or high performers. After the contest days, let's also discuss the problems here. Good luck to all participants! **UPD1**: [Day 1 results are here](http://info1cup.com/results) **UPD2**: There will be online mirrors on [Kilonova](https://kilonova.ro), and they will be available starting on Monday, until Friday evening: [Day 1](https://kilonova.ro/contests/1143) [Day 2](https://kilonova.ro/contests/1144) **UPD3**: [The final results are here](http://info1cup.com/results), huge congrats to Issatay Ismagzi for his win, representing ...

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RCPC 2023 on Gym Recently, the 2023 edition of the Romanian Collegiate Programming Contest took place in Iasi as part of the [RCPCamp](https://sites.google.com/view/rcpcamp2023/home), an international ICPC camp organized in Romania by the Alexandru Ioan Cuza University of Iasi (UAIC). I had the opportunity to coordinate RCPC this year and as the contest turned out to be an interesting and a challenging one, I posted the contest yesterday on gym. The contest can be accessed [here](https://codeforces.me/gym/104782). The problems were created and prepared by [user:RedstoneGamer22,2023-11-10], [user:andrei_iorgulescu,2023-11-10], [user:LucaLucaM,2023-11-10], [user:caheman,2023-11-10], [user:andrei_C1,2023-11-10], [user:divad,2023-11-10] and me. I also thank [user:pauldiac,2023-11-10] for giving us the chance to set this contest as well as [user:alex_vasiluta,2023-11-10] for the [Kilonova](https://kilonova.ro/) platform we used for holding the contests on both days of the camp. I hope you find...

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[JOI] JOI English Problem Editorials Hello, CodeForces! I am Cristofor Zaharescu, a teacher from Alunis, Romania. Very few of my more advanced students have started to solve JOI open, final round and summer camp contests. After not that much time of solving these sort of tasks, they have observed one thing — the fact that JOI editorials are pretty hard to find. They tried looking on announcement CodeForces blogs, but not all problems have a really detailed user-made comments, which can sometimes be useless if the problems is really hard and some key details are being left out. Plus, translating JOI slide-shows by hand is also a non practical thing to do, as translations are commonly inaccurate, and text selection in JOI editorials does not allow you to select numbers in the slide-show's text. I have decided to make this blog an organized place where anybody can find JOI explanations easily, but I need your help. If you have the time to do this, please make a separate comment for every JOI problem you ar...

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RCPCamp 2023 Day 1 On Gym About a month ago, the 2023 edition of the Romanian Collegiate Programming Contest took place in Iasi as part of RCPCamp, an international ICPC camp organized in Romania by the Alexandru Ioan Cuza University of Iasi (UAIC). The first day of RCPCamp was authored and prepared by myself, [user:Juve45,2023-11-27], [user:lungualex00,2023-11-27] and [user:tibinyte,2023-11-27]. We would like to thank the following people, who have played a pivotal role in making this contest possible: - [user:pauldiac,2023-11-27] for his excellent coordination of RCPCamp and for giving us the opportunity to set this contest. - [user:andrei_boaca,2023-11-27], [user:cristian1997,2023-11-27], [user:BlueDiamond,2023-11-27], [user:Amanda_LWA,2023-11-27], [user:denis2111,2023-11-27], [user:popabogdannnn,2023-11-27], [user:Sochu,2023-11-27] and [user:caheman,2023-11-27] for testing. - [user:Alex_Vasiluta,2023-11-27] for the [Kilonova](https://kilonova.ro) platform, which was used to host both contests ...

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The first round of the RoAlgo Cup Hello, codeforces! We are holding the first round of the RoAlgo Cup in less than 24 hours! **About RoAlgo and RoAlgo Cup** RoAlgo is the biggest algorithmic community in Romania, with over 3000 active members. The RoAlgo Cup is an open competiton held by members of this community. This is the first round and is expected to be enjoyable and educational in the rating range [pupil, grandmaster], featuring 8 problems roughly sorted by difficulty. The authors of this round are [user:SSKMF,2026-02-08], [user:RaduM,2026-02-08] and Alex Mihai Ioan. The contest will be held on [kilonova](http://kilonova.ro), link to the contest: [here](https://kilonova.ro/contests/2425). The starting time is **13 UTC on the 8th of February** and the duration is four hours. Hope to see you in the standings!

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IIOT Romanian National Round 2023 Mirror Hello, Codeforces! We are holding a mirror for the recent Romanian IIOT National Round. [IIOT](https://codeforces.me/blog/entry/108619) (International Informatics Olympiads in Teams) is a team olympiad for teams of 4 highschool students organised in collaboration with Italy, Hungary and Syria. Some details about the contest: - The mirror is taking place on [Kilonova](https://kilonova.ro). Here is the contest [link](https://kilonova.ro/contests/4/). - The mirror is **USACO style**, meaning that the mirror is open till **23:59PM March 12th (GMT+2 time)**, but you can choose **any 3 hour window** before then. You will have **6 problems** of various difficulties. Based on the onsite results, we believe that some problems might be challenging even for some grandmasters. - The statements are written in **English**. - The supported languages are C, C++, Go and Python. - The Romanian writers and contributors for this year's rounds are: [user:bicsi,2023-03-05], [user:giotoz...

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Competitive Companion — Parse problems from the browser Hi! After releasing [CHelper Companion](http://codeforces.me/blog/entry/56275) as an alternative to the original CHelper extension six months ago, development has been ongoing and CHelper Companion has "evolved" into [Competitive Companion](https://github.com/jmerle/competitive-companion). Competitive Companion is a browser extension for [Chrome](https://chrome.google.com/webstore/detail/chelper-companion/cjnmckjndlpiamhfimnnjmnckgghkjbl) and [Firefox](https://addons.mozilla.org/en-US/firefox/addon/competitive-companion/) that can parse problems and contests and extract the useful data. This includes things like time/memory constraints and sample test cases. While CHelper Companion was only capable of sending this data to CHelper, Competitive Companion works with pretty much all popular tools. Next to that, Competitive Companion is also capable of sending the data to your private tools, without requiring a complex setup. Using it is very simple. Just install the extension, make ...

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A very interesting problem. Hello, codeforces! As you can observe from my rank, I am quite a codeforces newbie. I spend all my days on the sacred romanian OJ, Infoarena( https://www.infoarena.ro/ ), and, more recently, Kilonova( https://kilonova.ro/ ). Altough the blue color is dominating my profile and I should not be taken seriously for such heresy, I want to share with the good people of codeforces an interesting problem. Please do not bully me, despite my little experience. I would be honored to hear your opinion. This is the problem: You are given a string S of digits separated by the following operators: +, *, -, /, ^(pow), $(xor), &, |, (, ). Parentheses have biggest priority, then: '^'(pow) > '/' > '*' > '+' > '-' > '&' > '|' > '$'(xor). The task is to find out in how many ways modulo 10^9 + 7 you can rearrange the characters of the string such that the result is a given X(X < 10). |S| <= 2 * 10 ^ 5. Time limit: 0.01 seconds Memory limit: common sense I know how to solve this problem,...

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