오랜만이에요, 코드포스! (Long time no see, Codeforces!)

I'd like to welcome all of you to Codeforces Round #688 (Div. 2)! The contest will start at Dec/04/2020 16:05 (Moscow time), and it is rated for all participants with ratings under 2100. Note the semi-unusual start time.

You will be given 6 problems and 2 hours and 15 minutes to solve them. The score distribution will be announced soon.

All problems are prepared by me, with a lot of help from the testers making me realize that my solutions are dumb.

Thanks to Green55, JooDdae, cs71107, CodePlatina, FlowerOfSorrow, jh05013, Anus1373, 39dll, alswhp, Ku_Top, sonjaewon, slah007, jooncco, and __rkm__ for testing the round, and especially xiaowuc1 for helping polish English statements as well. I would also like to thank 300iq for round coordination, and MikeMirzayanov for the great Codeforces and Polygon system.

See you in the round!

UPD: The scoring distribution is 500 — 1000 — 1500 — 2000 — 2500 — 3500.

Hello Codeforces!

On Nov/30/2020 17:35 (Moscow time) Educational Codeforces Round 99 (Rated for Div. 2) will start.

Series of Educational Rounds continue being held as Harbour.Space University initiative! You can read the details about the cooperation between Harbour.Space University and Codeforces in the blog post.

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 Roman Roms Glazov, Adilbek adedalic Dalabaev, Vladimir vovuh Petrov, Ivan BledDest Androsov, Maksim Ne0n25 Mescheryakov and me. Also huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Good luck to all the participants!

Congratulations to the winners:

Congratulations to the best hackers:

And finally people who were the first to solve each problem:

UPD: Editorial is out

Hello Codeforces!

One of the most memorable Kotlin rounds of this year took place just recently. More than 6.7 thousand participants have registered for it. We thank everyone for your interest in Kotlin! Everyone who took part in this round will receive a link to download a personalized online certificate within the next two weeks. Work on this has already started.

Our warm congratulations to the winners of the 1st, 2nd, and 3rd place, who receive cash prizes:

1. tourist
2. Benq
3. Geothermal

A Kotlin Heroes t-shirt and exclusive Kotlin stickers will be presented to:

And also these participants won branded T-shirts:

Finally, the last, but not least, gift for today: ICPC-experience, an invitation to the Moscow World Finals 2021, all-inclusive on-site (hotel, meals, ceremonies, and swag, are included; visa, flights, transportation to the contest location is not).

And a special recognition prize from the ICPC goes to tourist.

If you are still new to Kotlin you could look into a tutorial on competitive programming in Kotlin and watch these videos on competitive programming in Kotlin. Also, all the previous Kotlin Heroes Rounds are available for practice here: Episode 1, Episode 2, Episode 3, Episode 4 and Episode 5: ICPC Round.

We wish you all the best and hope you enjoy Kotlin.

Hi all!

This weekend, at Nov/29/2020 10:05 (Moscow time) we will hold Codeforces Round 687. It is based on problems of Technocup 2021 Elimination Round 2 that will be held at the same time.

Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at Technocup 2021 website and take part in the Elimination Round.

Div. 1 and Div.2 editions are open and rated for everyone. Register and enjoy the contests!

The problems authors are; amethyst0, eidan, Diegogrc, bensonlzl, Maripium, antontrygubO_o, and KAN. Thanks to antontrygubO_o and 300iq for their help in coordination. Also huge thanks to testers for their invaluable help: Golovanov399, __rkm__, golions, dantrag, postscript, barakraganosungam, Andres_Alumets, firiexp, growup974, Nero, GGMU, K0u1e, Bench0310, dorijanlendvaj, Um_nik, thenymphsofdelphi, Merkurev, Constantius, wucstdio, ayushsinghiitr, abhishhh1!

Have fun!

Thank you for participation! We hope you enjoyed the problems. Congratulations to winners!

Technocup 2021 - Elimination Round 2

1. Kirill22
2. 8-_-8
3. VEGAnn
4. alexxela12345
5. IdoItMyWay

Codeforces Round #687 (Div. 1, based on Technocup 2021 Elimination Round 2)

1. ecnerwala
2. ainta
3. conflict
4. al13n
5. kort0n

Codeforces Round #687 (Div. 2, based on Technocup 2021 Elimination Round 2)

1. gang_leader
2. iLoveIOI
3. heavyshower
4. xaohu
5. wsr_oier

Upd: Rating updates published.

UPD2: The editorial is published.

Hello! Codeforces Round #686 (Div. 3) will start at Nov/24/2020 17:35 (Moscow time). You will be offered 6 or 7 problems (or 8) with expected difficulties to compose an interesting competition for participants with ratings up to 1600. 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 — just like you will be upset if many solutions fail after the contest is over.

You will be given 6 or 7 (or 8) problems and 2 hours to solve them.

Note that the penalty for the wrong submission in this round (and the following Div. 3 rounds) is 10 minutes.

Remember that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsporting behavior. To qualify as a trusted participants of the third division, you must:

• take part in at least two rated rounds (and solve at least one problem in each of them),
• do not have a point of 1900 or higher in the rating.

Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600, then the round will be rated for you.

Thanks to MikeMirzayanov for the platform, help with ideas for problems and for coordination of my work. Thanks to my good friends Daria ZeroAmbition Stepanova, Mikhail pikmike Piklyaev, Maksim Ne0n25 Mescheryakov and Ivan BledDest Androsov for help in round preparation and testing the round. Also thanks to Artem Rox Plotkin and Dmitrii _overrated_ Umnov for the discussion of ideas and testing the round!

Good luck!

UPD: I would also like to thank Ivan Gassa Kazmenko for invaluable help with the round preparation!

UPD2: Editorial is published!

Hi everyone!

I would like to invite you to another one of our rounds, that I set with my friends Jeel_Vaishnav, FastestFinger, Utkarsh.25Dec, the_hyp0cr1t3 and ridbit10

We had two approved contests, but decided to merge it into one with more logical thinking ^_^

The round Codeforces Round #685 (Div. 2) that will take place on 21.11.2020 17:35 (Московское время). If your rating is less than 2100, this round will be rated for you; otherwise, you can participate out of competition.

I would really like to thank my co-setters and:

• 300iq for coordinating our round and always replying quickly.
• jtnydv25, antontrygubO_o, Monogon, Vivek1998299, tejas10p, smit_mandavia, T1duS, kshitij_sodani, ayushsinghiitr, Ajax, JeevanJyot, ViciousCoder, Prozac, vatsals1, saarang123, Dragon_warrior_iitk, sac2607, matterhunt, matir, Black_Eye, vatsal_nagelia, __rkm__, ekanshi, glitched and vishesh312 for testing the problems.
• the_hyp0cr1t3 and ExplodingFreeze for testing as well as proofreading and making suggestions for the problems.
• MikeMirzayanov for Codeforces and Polygon platforms.

You will be given 6 problems with one additional subtask and 2 hours 15 minutes to solve them.

Good luck — let the games begin :D

UPD 1: The revised scoring distribution will be: $$$500 - 750 - 1250 - 1750 - (1500 + 1000) - 3000$$$

UPD 2: Editorial — Hope you guys enjoyed the round, we will hopefully be back sometime next year :)

UPD 3: Congratulations to the winners! :D

All Participants:

1. noimi
2. I_Love_Convex_Hull
3. zhouzhendong
4. dlalswp25
5. peti1234

Official Participants:

1. I_Love_Convex_Hull
2. 221
3. afterall
4. Khas_Profit_LLC
5. imzzy

Приглашаем учащихся 7-11 классов из России и иностранных государств проявить себя в Олимпиаде по информатике «Innopolis Open».

Этапы проведения олимпиады:

Отборочный этап

Состоит из двух независимых отборочных онлайн-туров, продолжительность каждого 5 часов. В рамках него участникам предлагается по 4—5 задач по информатике.

• 1-й отборочный тур: 22 ноября 2020 г. 10:00 — 15:00 МСК
• 2-й отборочный тур: 13 декабря 2020 г. 15:00 — 20:00 МСК

Участник может пройти оба тура, тогда в отборе будет учитываться лучший результат по итогам двух туров. Победители и призеры Innopolis Open по информатике 2020 приглашаются на заключительный этап без отбора.

Отборочный этап также является отбором на Зимнюю школу олимпиадной подготовки по информатике 12—19 февраля 2021.

Финал

20—21 февраля 2021 г.

Формат проведения (очно или заочно) заключительного этапа остается под вопросом. В случае очного формата финал будет распределен на нескольких площадках по России и другим странам. Главная площадка будет в Иннополисе.

Innopolis Open 2021 по информатике имеет 2 уровень перечня РСОШ, что позволит победителям и призёрам олимпиады получить преимущество при поступлении в Университет Иннополис и другие вузы.

Регистрация

По всем вопросам: olymp@innopolis.ru

Hello Codeforces!

There is something new for you. It seems that now it will be easier to reuse problems from the archive for educational and other purposes.

As you know, problems from past Codeforces rounds can be added to mashups simply by their codes of the form like 1234D (contest ID + problem letter). I myself regularly used this when I taught at Saratov University — it was very convenient to prepare trainings: problems have expected complexity and topics, there are Russian and English statements, you can see the analysis and many solutions. Because of hacks and uphacks, problems in the archive usually have strong tests. Almost all of them are well-prepared. In addition, with the help of user lists, you can easily pick up problems for a group of students that they did not solve.

But there was also an issue: the problems in such trainings were easily googled. And if the majority of adult participants could cope with the temptation to spy on the solution or tests, then beginners sometimes acted dishonestly. I received several requests to come up with something with this flaw. One of the most recent such requests was from Daniel Darooha Sleator (https://en.wikipedia.org/wiki/Daniel_Sleator). Thanks, Danny!

So the work seems to be complete. Meet a new feature on Codeforces: now you can rewrite statements for problems in mashups, completely replacing it with your own. More details about the capabilities of the new functionality:

• a new icon-link appears in the problem list in mashups, by clicking on which there will be a form for creating/editing a new statement;
• you can use the original text of the statement as a template when writing your own: be very careful — you must exactly repeat all the details of a statement so that problems do not formally differ;
• this form compares the set of formulas in the original text and the new statement, and if they differ as sets, there will be a corresponding detailed warning;
• you can specify your own tests from a statement (examples) — here you also need to be very careful so that they are formally correct;
• if you added examples, then solutions will be judged on them first, and only after on official tests;
• you can upload your own image files and use them in statements;
• there is a setting to temporarily disable the use of the new statement (for example, if it is still under development).

Considering that there are already more than 6500 problems in the archive, an excellent perspective opens up for organizing trainings and educational sessions.

I hope this innovation will be useful. Write in the comments what can be improved and/or corrected.

M.