Hello, codeforces.

To unveil the full power of Kotlin and JetBrains tools, as well as their advantages in algorithmic problem-solving, we’ve invited two competitive programming stars to match their skills in solving Kotlin problems on stage at the ICPC World Finals.

Andrew ecnerwala He, one of the top competitive programmers in the world, will compete in a match against Kamil Errichto Debowski, Codeforces "Legendary Grandmaster" and Topcoder "Target." The match will be commentated by none other than Roman elizarov Elizarov, Kotlin Lead Language Designer.

You can join the stream on Kotlin by JetBrains youtube channel at 07.11.2022 07:17 (Московское время) and view submissions in the special Codeforces round Ecnerwala vs Errichto Kotlin Match. Only ecnerwala and Errichto can participate in the round, while you will be able to join as spectators.

We will reuse some problems from previous Div3 rounds. We mostly used round #748. And also, one problem was from round #627. A lot of thanks to MikeMirzayanov vovuh and MrPaul_TUser.

Good luck to both participants, and thanks to MikeMirzayanov for the great codeforces platform.

The International Olympiad in Informatics 2022 is scheduled to start in a month. To help you prepare today, we announce an online judge with IOI problems. Right here, on codeforces.

Available now

On https://ioi.contest.codeforces.com/ you can find a contest for each day of each IOI contest since 2002. Participate virtually in a 5-hour contest or simply upsolve problems there! Virtual participants will appear in separate scoreboards for each year as well as in an upsolving scoreboard. Don’t forget to disable coach mode to appear in the upsolving scoreboard.

Future work

We have at least some problem materials for contests since 1998, but IOI has had competitive programming problems since 1994. Even if these problems are not very useful for training, they have significant historical value. Unfortunately, early-year materials on ioinformatics.org are incredibly bad, so if you have something (e.g., solutions, interactor, checkers, library sources), please contact me right away!

I am also considering adding original contest results as ghost participants to the scoreboards.

Let me know in the comments, what else would you like to see in the IOI archive?

How to help?

I'm sure some problems are misconfigured. The most probable errors are tests in wrong subtasks or changes in grader not mentioned in the problem statements. Let’s find them in upsolving mode, to avoid ruining the training process for contestants. If you have solutions (preferably partial solutions), please, become an early tester. Report issues via github repo. Pull requests to problem statements and validators are also always welcome there!

Please, contribute with contest materials for earlier IOI!

If you are a member of an IOI committee, help the project a lot by enforcing a better archival process for the future contests. In particular, it would be great to have as part of the public archive:

• Statements in markdown
• Any kind of non-English statements
• Test data generators and tests generation command lines
• Any description of solutions intended behavior or score
• no new archive format every year :)

Also, you can donate to pavelkunyavskiy.crowdforces.near, to help pay for outsourcing some work, but that’s not necessary.

Special thanks

• MikeMirzayanov and geranazavr555 for implementing a lot of stuff in Codeforces and Polygon
• ligaydima , Dimitrys and especially Masha237 for help converting problem statements to polygon format.
• lperovskaya for maintaining archive on contest.yandex.ru/ioi, which become a great material source, as well as for proofreading this text
• Petr for solutions and other materials of IOI2002 (and IOI2000, and IOI2001 I hope to publish later).
• eduardische for showing me the old IOI site with problem materials, and Martins Opmanis for maintaining it.
• yeputons for original archive resources and idea back in 2011
• Mazaalai for better than original one solutions of IOI2003-reverse

Updates

10.08.2022: IOI 2022 day 1 is available.
13.08.2022: IOI 2022 day 2 is available.
30.08.2023: IOI 2023 day 1 is available.
01.09.2023: IOI 2023 day 2 is available.

Today we will celebrate the winners of the VK Cup 2019-2020! Even though finalists will not get together on the New Stage of Alexandrinsky Theatre in St. Petersburg, as initially planned, they will battle for the bragging rights to be called VK Cup Champion and the grand prize of 524 288 rubles. Best of luck to all the finalists!

On Nov/02/2020 17:35 (Moscow time) we invite everyone to participate in Codeforces Round 681 (Div. 1, based on VK Cup 2019-2020 - Final) and Codeforces Round 681 (Div. 2, based on VK Cup 2019-2020 - Final).

VK Cup problems are created and prepared by 300iq together with the VK team PavelKunyavskiy, izban, YakutovDmitriy, Kurpilyansky and .tx. Additional problems for codeforces rounds were authored and prepared by Supermagzzz, Stepavly and MikeMirzayanov.

We’d like to thank for the huge help in preparing and testing the problems MikeMirzayanov, ecnerwala, Egor, hos.lyric, yosupo, lperovskaya, Stepavly, Supermagzzz, HIR180, qwerty787788.

Good luck and have fun!

UPD: And the winners are:

1. tourist
2. Endagorion
3. Merkurev

Congratulations! Full scoreboard is available here.

UPD:

Div.1 Scoring: 500 1000 1500 1750 1750 2500

Div.2 Scoring: 500 1000 1500 2000 2500 3000

UPD: Editorial

Everyone on this site heard about problem preparing tool, maintained by MikeMirzayanov called polygon.

It have a lot of advantages, like automatic checks of everything you can imagine. But also, it have several very annoying things. The main one for me is necessity of synchronizing solutions and generators files by hand, between polygon and your local copy. So I had written a tool, which can do it.

Tool is published on github, with instructions how to install it. You are welcome with any new features/suggestions (I'm not knowing python very well, to be honest).

Known problems:

• Not tested good enough, probably buggy
• Installation script working strange. Anyone knowing python better? Any better ways to distribute?
• Sometimes lost of session is not detected and script fails with strange non-readable errors. relogin helps
• Parsing html pages can be not stable enough with changing polygon. Waiting for better api from MikeMirzayanov and codeforces team.

Two years ago (or something like that) GCJ problemsetters announced commandline-tool, which can download input, make submissions, and view current contest state. It support was not very long, but before last contest it worked as is (at least downloading and submitting).

Before last contest I discovered, it can't login to google account because it get HTTP 404 error. Any ideas what got wrong and how to fix it?

Also I'm interested if anyone else, except me, use it?

Good time of the day.

As some of you know, yeputons and I have an archive of IOI-tasks. While preparing it, we had understood, that we have no resources to prepare graders for all languages,so we want to find a way to write a grader only for C, and to link other languages to it.. Also, I think it's better to have one grader and adapters to avoid code duplicating, which can cause errors.

There were some problems with linking Pascal, but they were mostly solved. I'll write about one unsolved problem further. It would be very good if someone have ideas how to solve it.

Next year Java will be available on IOI. So I tried to write Java adapter for graders. Here is one for the problem 2010.cluedo. I think this one works well.

I publish this because I think someone else can be interested in it. Also I have some problems, which I don't know how to solve. Probably someone here can solve them.

First of all, we need to include jni.h. But it doesn't belong to gcc library path. So we need to set path, which depends on computer settings (path to java, to be more precise).
Also this way is quite complicated to compile. I don't know how to do this in some IDE, which is probably used by participant using java. And participant probably don't know what is jni, and how to do something like this.
The same problem happens to pascal. Also there is one extra problem. FPC needs libc to link this. And I don't know way to find libc on windows. libmsvcrt.a from MinGW is ok. But how to find it on participants computer? And what to do, if he is using some other compiler? Also, participant needs C-compiler to use Pascal, and that is not very good.

All this problems are not really important on competition (as we know settings of participants computers), but if we use on-line judge for it we will face the above-mentioned problems.

I hope there is someone from ISC or some other IOI structures, who can help with it, who is reading Codeforces. Anyway, if you have some ideas how to make this better, or any comments, I will be very interested in it.

Topcoder SRM 600 will be held next Saturday in 21:00 MSK

On round they promise 120 t-shirts for Div.1 and 40 t-shirts for Div.2, half for top ranked, and half the participants randomly chosen among having more zero points.

But that's not all. On Sunday 21:00 MSK there will be held non-rated SRM 600.5 (Special Round Match). Where there will be 40 more t-shits and 600$ prize for first place. Round will have duration of 4 hours and consists of two tasks, which did not give on-sight TCO as too complex and one Div1-Hard level. Besides the top 40 with a nonzero score promise 10 t-shirts for random spectators (people who were logged in the arena more than 3 hours of 4).

UPD: Since this match TL and ML are indicated in the problem. The authors say that they will try to use TL 2 seconds and ML 256 MB for most porblems. (used to be 64MB)

Hello!

We are happy to invite you to participate in today's round. I hope everyone will find interesting problems for him. And most of the round participants will like it as well as the previous one.

Today's contest was prepared for you by SPb SU 4 team (Alex-Gran (Alexandr Granovskiy), Dmitry_Egorov (Dmitry Egorov), PavelKunyavskiy (Pavel Kunyavskiy)). After long thoughts you can notice that we present St.Petersburg State University.

Thanks very much for help in the tasks preparation to Artem Rakhov(RAD), Gerald Agapov (Gerald) and Maria Belova (Delinur) for translation statements. Also thanks to Petr Kalinin (KAP) for statements proofreading.

In today's contest there will be seven problems (5 in each division) about the country where wizards live, and this causes many interesting events. Today you have to take part in local meeting, understand the intricacies of writing spells, ride on the magic transport, try to take away magic prizes, play in popular wizards game, help magic government in ruling the country and resolve financial dispute of two famous wizards.

Scoring is standard is standard in both divisions today (500-1000-1500-2000-2500).

UPD: analyse was published.

Good luck!