BOI 2022  This weekend, the **Baltic Olympiad in Informatics 2022** (BOI 2022) is going to take place! BOI is a programming contest for secondary school students from countries around or close to the Baltic sea. This year, around 70 contestants from Denmark, Estonia, Finland, Germany, Iceland, Latvia, Lithuania, Norway, Poland, Sweden and our guest countries Israel and Ukraine will compete against each other, solving difficult problems of algorithmic nature. Each participating country sends 6 contestants from their national olympiads which take place in the months beforehand. The contest consists of two days, Saturday and Sunday, on each of which the contestants have 5 hours to solve 3 problems of varying difficulty. Each problem is worth 100 points that are distributed into multiple subtasks with different constraints that allow the participants to earn partial scores. During the contest, each participant receives the...

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BOI 2021 The year is 2021. Like every year, contestants from all of the baltic countries meet for the Baltic Olympiad in Informatics. Well, not entirely... One small virus still holds the entire world under its spell. And life is not easy for BOI contestants who have to participate remotely from their own homes...  This weekend, the **Baltic Olympiad in Informatics 2021** (BOI 2021) is going to take place! BOI is a programming contest for secondary school students from countries around or close to the Baltic sea. This year, around 60 contestants from Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Norway, Poland, Sweden and our guest countries Israel and Ukraine will compete against each other, solving difficult problems of algorithmic nature. Each participating country sends 6 contestants from their national olympiads which take place in the months beforehand. The contest consists of two days, Saturday an...

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Osijek Competitive Programming Camp, Fall 2023 Hi everyone! <center><a href="https://ocpc.mathos.unios.hr"><img src="https://ocpc.mathos.unios.hr/images/ocpc.svg" height="100px"></a> <a href="https://icpc.foundation/"><img src="https://ocpc.mathos.unios.hr/images/ICPC.svg" height="100px"></a></center> <center> <b>Sponsored by</b><br> <a href="https://www.janestreet.com/join-jane-street/open-roles/?type=students-and-new-grads&location=london"> <img src="/predownloaded/ee/f2/eef26616a3661c658d1545f18ed21fabb14d5871.svg" height="50px" style="margin: 5px 5px 5px 5px;"> </a> <a href="https://pinely.com/"> <img src="/predownloaded/0a/0f/0a0f3f67435d1f6e467bc7203d4a2090ba8f92cc.svg" height="50px" style="margin: 5px 5px 5px 5px;"> </a> </center> After a successful camp last February ([announcement](https://mirror.codeforces.com/blog/entry/110945), [wrap-up](https://mirror.codeforces.com/blog/entry/113438)), we are happy to announce that Osijek camp will be returning on **16.-24. September 2023** &mdash; just in time to prepare for th...

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[2026 in progress] [v1.0.1] OI-TED-ARCHIVE — Preserve OI resources before they disappear **MEGA TORRENT BLOG:** https://mirror.codeforces.com/blog/entry/151059 v1.1.0 is coming soon in upcoming months. Goodluck for IOI2026, APIO2026 and Other OI2026. BOI2026 Uploaded to internet archive --- # OI-TED-ARCHIVE **OI Tasks + Editorial + Testdata Archive (+ Graders & Results)** **Goal:** Preserve complete Olympiad in Informatics resources before they disappear. --- ## Current Status **Latest progress:** https://docs.google.com/spreadsheets/d/1XPHTMTUGaKrDvCvNyh6LWuWEddNSxwxJhEB2NlUezOI/edit?usp=sharing For Upcoming Problems, 2 Major release will be made each year. Expect First Update around July-Auguest. --- ## OI-TED-ARCHIVE LINKs > Check Sheet ["ARCHIVE"](https://docs.google.com/spreadsheets/d/1XPHTMTUGaKrDvCvNyh6LWuWEddNSxwxJhEB2NlUezOI/edit?gid=118823279#gid=118823279) for Detailed & Updated Archive Info > Items List: https://archive.org/details/@moon_moonlight_144/lists/1/oi-ted-archive > Check Changelog Section in this Blog for detailed tab...

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Huawei IOI/EGOI/CEOI/etc. Camp 2025 [registration started] - [2022 recordings](https://www.youtube.com/playlist?list=PLg_Krngrs0eC_1vn0dTjyPZMkwBOcVsgH) &mdash; CEOI 2016, CEOI 2017, CEOI 2022, optimization problems, segment tree nodes - [2023 recordings](https://www.youtube.com/playlist?list=PLg_Krngrs0eAN_QrR5MKnaZROHVSCaQiL) &mdash; POI 2019, POI 2022, CEOI 2018, graphs - [2024 recordings](https://www.youtube.com/playlist?list=PLg_Krngrs0eCfvefczNWB-c-Af3BUSH0x) &mdash; POI 2016, POI 2019 mix, POI 2023, IOI 2014, lazy propagation, sweep line, partial dp/bfs (Bombs) Hi! For a fourth time, I'm organizing an online IOI camp sponsored by Huawei. It's free for IOI participants and coaches. **UPDATE**: we will accept participants of regional olympiads too (from this year, so e.g. BOI/EGOI/CEOI/APIO 2025)! Every day will be a 5-hour virtual contest, the problem analysis, and sometimes a lecture. - Dates: 17-23.07 (6 training days; Sunday off) - Contests: IOI 2015, POI 2024 and something else from POI/BOI/CEOI - **[EDIT]** Registration: Y...

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Moldova IOI and EGOI teams Hello codeforces. As you could probably see in my previous posts, recently team selections ended in our country. Now the teams for IOI/BOI and EGOI are defined: IOI/BOI team:  [user:SlavicG,2022-05-04] [user:KrowSavcik,2022-05-04] [user:RedFlea,2022-05-04] [user:_Vanilla_,2022-01-30] EGOI team:  [user:SlavicG,2020-04-03] [user:KrowSavcik,2021-01-04] [user:RedFlea,2020-11-01] [user:_Vanilla_,2022-01-30]

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Huawei IOI Camp 2023 Here's [the previous edition](https://mirror.codeforces.com/blog/entry/104746) and [the video recordings](https://youtube.com/playlist?list=PLg_Krngrs0eC_1vn0dTjyPZMkwBOcVsgH) (CEOI 2016, 2017, 2022, two lectures). Hi. I'm again conducting an online IOI preparation camp in collaboration with Huawei. Every day will be a 5-hour virtual contest, the problem analysis, and sometimes a lecture. Contests will consist of POI problems, and there might be a single day from BOI or CEOI. The example lecture topics are those from Range Queries or Trees in [Usaco Guide Platinum](https://usaco.guide/plat). The camp is free for IOI 2023 participants and coaches. You can register a few extra students if you're a country team-leader (then send me a msg in CF or email at erri..to@gmail.com). There will be a Discord server and a leaderboard. For everybody else, the video recordings will be posted on Youtube after the camp. **Dates**: around 8-16.08 **Time** of every analysis/lecture: [14:00 UTC...

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Submissions skipped in GR23 Hi [user:MikeMirzayanov,2022-10-15], My submissions were skipped from today's contest due to plagiarism checker for problem E2. As stated by others, problem E2 had a very similar idea to BOI 2022 communication, and the main logic of the code from my solution was copied from a previous submission for that problem (https://oj.uz/submission/592003, you can see that this code was submitted months before this contest). I'm not sure whether this problem was intentionally copied or not &mdash; but I don't believe that I broke any Codeforces rules with this submission, since the source code was published before the contest started. Please review my case, thanks! EDIT: My submission https://mirror.codeforces.com/contest/1746/submission/176378653 EDIT 2: In case evidence of search history cache is needed (my time zone is GMT-7, so 8:47 AM on October 15th is during the contest for me): 

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Baltic OI 2022 It seems that the Baltic Olympiad in Informatics (BOI) 2022 is taking place. Since I didn't find any announcement, will there be a mirror contest this year?

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OI Duel Bot Hi, I made a duel bot where you can challenge other users in a OI styled duel. It is sort of like a combination of regular duel matches and lockout challenges. You can find the bot at [OIDuelBot](http://t.me/OIDuelBot). The bot is currently available only for Telegram, but I have plans to make one for discord as well. ### Rules You can challenge other users in a OI styled duel. In the duel, you have to race against time to solve the subtasks before your opponent. If your opponent solves a particular subtask before you, they gets the point for that subtask, and you won't get any points for it even if you solve it in the future. The player with more points at the end of the duel wins the challenge. ### How to use First, you need to add the bot in a telegram group. Here are the commands you can use in the bot `/register [oj.uz username]` &mdash; you have to register yourself in order to enter your duel `/challenge [telegram username]` &mdash; you can challenge other user...

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Anime Team Selections in Moldova Did you know Team Selections for IOI/BOI in Moldova are anime rounds? Photo from Team Selections with [user:SlavicG,2022-04-16] 

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Height-wise Small-to-Large Trick Hello Codeforces, I will present today, and in any day in the future, a means to correctly calculate a corner case of the well known small-to-large trick, and how this can be employed to solve a set of certain problems. This blog is written with encouragement from the [Month of Blog Posts](https://mirror.codeforces.com/blog/entry/133806) initiative. <spoiler summary="Forenote; Height definition"> The *height* of a node, as will be used throughout this blog, refers to the maximum distance in a rooted tree from a node to any of the leaves within its subtree. As a corollary, hereby it is considered that a leaf has a height of 1. </spoiler> ### The standard example. Let's try to solve the following problem: [Cat In a Tree, BOI 2017](https://oj.uz/problem/view/BOI17_catinatree). Although this problem can be solved employing some greedy algorithm, assume we have no idea what greedy is or how it could be correct, and revert to the basics: #### The standard DP. How can we formul...

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