(I'm too lazy to write a post so I copied last year's, thanks pooty)

Hello, Codeforces community!

We are happy to invite you to participate in National University of Singapore (NUS) CS3233 Final Team Contest 2024 Mirror on Monday, April 15, 2024, at 09:15 UTC. CS3233 is a course offered by NUS to prepare students in competitive problem solving.

The contest is unofficial and will be held in Codeforces Gym. Standard ICPC rules (Unrated, ICPC Rules, Teams Preferred) apply. The contest is unrated. Note the unusual starting time.

The problems are written and prepared by user202729_, rama_pang, yz_, benson1029, HuaJun, and feeder1.

We would also like to thank:

• Prof. Steven Halim for coordinating and teaching the CS3233 course;
• benson1029 and HuaJun as teaching assistants;
• stack.py (Pyqe, hocky, faustaadp), and Berted for testing the contest;
• errorgorn for existing;
• the Kattis team for the platform used in the CS3233 course and in the official contest;
• Codeforces Headquarters for letting us announce on the main page; and finally
• MikeMirzayanov for the amazing Codeforces and Polygon platform!

The contest will last for 5 hours and consist of 13 problems. While it is preferred to participate in a team, individual participation is also allowed.

The problems themselves may be quite standard as they are targeted toward those who have just learned competitive problem solving. However, we have also included a few challenging problems for stronger teams, such as ex-IOI or ICPC participants taking part in the course as well. So, the participants can expect a good mix of problems of varying difficulty levels, that we hope can be educational!

We hope you will enjoy and have fun in the contest. Good luck!

UPD: The contest is over! Here is the editorial.

Ciallo, codeforces～(∠・ω< )⌒☆

We are pleased to invite you to participate in Codeforces Round 939 (Div. 2), which will start on Apr/13/2024 17:35 (Moscow time).

The problems are from Otomachi_Una and me.

This round will be rated for participants whose rating is below 2100. Participants with higher ratings may participate out of the competition.

You will be given 6 problems and 2 hours to solve them. We hope you find them interesting.

We would like to thank:

• DaiRuiChen007 and lichenghan for helping prepare this contest.
• IgorI and irkstepanov for coordinating the round.
• A_G, NemanjaSo2005, yeminghan, lunchbox, Andreasyan, lsantire, RabbieWjy, yurongyi0504, KKT_89, MinaRagy06, carnation13, Romakolesn, blitztage, qsc114, Adam_GS, Evarine and htetgm for testing.
• MikeMirzayanov for Codeforces and Polygon platforms.

Score distribution: $$$500-750-1500-1750-(1500+750)-2500$$$

Good luck on the round and high rankings to everyone!

UPD: Editorial out.

UPD: the winners

Photo of authors (unfortunately, I can't come, so my profile is shown in the picture):

UPD: The rating changes for Educational Codeforces Round 164 will be applied after this round.

Привет, Codeforces!

Благодаря поддержке Neapolis University Pafos, продолжается серия образовательных раундов.

В 12.04.2024 17:35 (Московское время) состоится Educational Codeforces Round 164 (Rated for Div. 2).

Этот раунд будет рейтинговым для участников с рейтингом менее 2100. Соревнование будет проводиться по немного расширенным правилам ICPC. Штраф за каждую неверную посылку до посылки, являющейся полным решением, равен 10 минутам. После окончания раунда будет период времени длительностью в 12 часов, 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 или 7 задач на 2 часа. Мы надеемся, что вам они покажутся интересными.

Задачи вместе со мной придумывали и готовили Адилбек adedalic Далабаев, Иван BledDest Андросов, Максим Neon Мещеряков и Роман Roms Глазов. Также большое спасибо Михаилу MikeMirzayanov Мирзаянову за системы Polygon и Codeforces.

Спасибо тестеру раунда shnirelman за ценные советы и предложения!

Удачи в раунде! Успешных решений!

UPD: Разбор опубликован

Привет! В Apr/08/2024 17:35 (Moscow time) начнётся Codeforces Round 938 (Div. 3) — очередной Codeforces раунд для третьего дивизиона. В этом раунде будет 6-8 задач, которые подобраны по сложности так, чтобы составить интересное соревнование для участников с рейтингами до 1600. Однако все желающие, чей рейтинг 1600 и выше могут зарегистрироваться на раунд вне конкурса.

Раунд пройдет по правилам образовательных раундов. Таким образом, во время раунда задачи будут тестироваться на предварительных тестах, а после раунда будет 12-ти часовая фаза открытых взломов. Мы постарались сделать приличные тесты — так же как и вы, мы будем расстроены, если у многих будут падать решения после окончания контеста.

Вам будет предложено 6-8 задач и 2 часа 15 минут на их решение.

Штраф за неверную попытку в этом раунде будет равняться 10 минутам.

Напоминаем, что в таблицу официальных результатов попадут только достоверные участники третьего дивизиона. Как написано по ссылке — это вынужденная мера для борьбы с неспортивным поведением. Для квалификации в качестве достоверного участника третьего дивизиона надо:

• принять участие не менее чем в пяти рейтинговых раундах (и решить в каждом из них хотя бы одну задачу)
• не иметь в рейтинге точку 1900 или выше.

Независимо от того являетесь вы достоверными участниками третьего дивизиона или нет, если ваш рейтинг менее 1600, то раунд для вас будет рейтинговым.

Задачи были придуманы и написаны нашей командой: mainyutin, vmanosin7, ssor96 и ZergTricky.

Также большое спасибо:

1. Vladosiya за помощь с идеями и прекрасную координацию раунда;

2. FairyWinx, sevlll777 за красное тестирование раунда;

3. ace5, Nickir, senjougaharin, vladmart за жёлтое тестирование раунда;

4. natalina за синее тестирование раунда;

5. bitthal04 за бирюзовое тестирование раунда;

6. Alequisk, Mohamed_Hesham за зелёное тестирование раунда;

7. MikeMirzayanov за системы Polygon и Codeforces.

Всем удачи!

UPD: В задаче G была допущена ошибка с валидацией взломов, но сейчас она уже исправлена. Все успешные взломы будут перетестированы. Ошибка не затронула претесты, они не будут изменены.

UPD2: Разбор опубликован.

Xin chào Codeforces (・ω・)ﾉ

We are pleased to announce the resumption of the Global Rounds. Thanks to XTX Markets for supporting the initiative! In 2024, we will hold 4 such rounds. The series results will take into account the best 3 participations out of 4.

On Apr/06/2024 17:35 (Moscow time) we will host Codeforces Global Round 25.

Codeforces Global Round 25 marks the first round in the 2024 series of Codeforces Global Rounds. These rounds are open and rated for everyone.

The prizes for this round are as follows:

• The top 30 participants will receive a t-shirt.
• 20 t-shirts will be randomly distributed among participants ranked between 31 and 500, inclusive.

The prizes for the 4-round series in 2024:

• In each round, the top-100 participants get points according to the table.
• A participant's final score will be the sum of the points they earned in their 3 highest-placing rounds.
• The top 20 participants across the series will receive sweatshirts and placement certificates.

We extend our gratitude to XTX Markets for supporting the global rounds initiative in 2024!

The problems were all marinated and cooked by MofK and Kuroni.

Our sincerest gratitudes go to:

• errorgorn for being the 🥶 and 😭 coordinator, and TheScrasse for being the 🧌 coordinator.
• xuanquang1999, gamegame, zeena., lanhf, Sana, TrungNotChung, lmqzzz, Umi, imsuck12, Saacoota, htetgm, kodomo_tachi, shine_, uocgimauxam, Pemguimn, Bananabread, hphuong, DeMen100ns, Kriz_Wu, milind0110, YangJackie, Vladithur, Ann, Endagorion, richzli, BucketPotato, and _FireGhost_ for testing and ensuring the balance of the round.
• Alexdat2000 for translating the statements to Russian.
• And of course, MikeMirzayanov for Codeforces and Polygon.

Round Information:

• Duration: $$$3$$$ hours.
• Number of problems: $$$9$$$ problems.
• Score distribution: $$$500 - 1000 - 1500 - 1750 - 2250 - 2750 - 3250 - 3500 - 4000$$$.

A tiny bit of personal note at the end, this is our first round on Codeforces in 3 years, and it feels a bit nostalgic to be back here again :) We eagerly anticipate your participation and let's all make it an awesome contest together!

UPD: Added score distribution.

UPD: The round has concluded. Congratulations to the winners!

1. Geothermal
2. ecnerwala
3. Um_nik
4. maroonrk
5. jqdai0815
6. Benq
7. hos.lyric
8. antontrygubO_o
9. cmll02
10. AlternatingCurrent

Tutorial can be found here, and playlist of songs used in the problem statements can be found here.

Привет, Codeforces!

Мы, AlperenT, flamestorm, ToxicPie9 и willy108, приглашаем всех на Codeforces на April Fools Day Contest 2024! 12-й Конкурс первоапрельских розыгрышей пройдет 01.04.2024 17:35 (Московское время). Это шутливое соревнование, в котором решение задачи часто проще, чем понять, что за задача вообще.

В этом раунде вам будет дано $$$n$$$ крутых багабу, где $$$-1 \le n \le \textbf{[REDACTED]}$$$, и 2 часа для их решения. В конкурсе будут использоваться расширенные правила ICPC (нет хаков, позиции определяются количеством решенных задач и штрафным временем, полученным за них). Вы можете отправлять решения на любом языке, разрешенном на Codeforces, если задача не указывает обратного.

Обратите внимание, что раунд не рейтинговый, и штраф за неправильное решение составляет 10 минут.

Чтобы представить, как будет выглядеть контест, вы можете посмотреть на контесты предыдущих лет: 2012, 2013, 2014, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023. (Прошло 12 лет с первого Конкурса первоапрельских розыгрышей, спасибо Nickolas!)

Пожалуйста, не отправляйте никаких запросов на уточнение во время контеста, так как мы определенно не будем отправлять забавные ответы, как в прошлом году.

Удачи и веселитесь!

Hello Codeforcers!

We are pleased to invite you to participate in CodeTON Round 8 (Div. 1 + Div. 2, Rated, Prizes!). This round will start on Mar/30/2024 17:35 (Moscow time) and will be rated for all participants. There will be $$$8$$$ problems to be solved in $$$3$$$ hours, with one divided into two subtasks. Similar to USACO, you will help Farmer John and his cows resolve a series of first world problems. Be there or be square.

This round was cooked up by smax, sum, oursaco, cry, and buffering.

We would like to thank the following people for making the round possible:

• Our favorite cherry TheScrasse for the wonderful and speedy coordination.

• Our MVP testers, Benq, Geothermal, and rainboy, for dedicating so much time to reviewing problems, providing essential feedback, and perfecting the problemset.

• The rest of our testers for their unparalleled efforts: errorgorn, rqi, hyforces, LipArcanjo, MridulAhi, omeganot, darkkcyan, Phi-001, awesomeguy856, JagguBandar, camc, drdilyor, lethan3, rohit2593, willy108, WAtoAC2001, jay_jayjay, -1e11, evenvalue, lunchbox, kaztayev, kondasujay2, maxrgby, htetgm, thehunterjames, GlassesNerd, SunShine11, wozhenshuai, chromate00, I_FloPPed21, MrPavlito, priyanshu.p, ETL, yash_9a3b, Aurora__, nelsi_sousa, susvant, and myvaluska.

• Alexdat2000 for translating the statements to Russian.

• MikeMirzayanov for developing Codeforces and Polygon, or else this contest literally wouldn't exist.

• You, for participating!

Score Distribution:

$$$500 - 1000 - (1250 + 750) - 2250 - 2500 - 3000 - 3000 - 4500$$$

Editorial

Congratulations to our Winners and First Solves!

Top 5:

1. maroonrk

2. Radewoosh

3. ecnerwala

4. cnnfls_csy

5. orzdevinwang

First Solves:

A. A_G
B. jiangly
C1. ksun48
C2. turmax
D. Omer223
E. tourist
F. Radewoosh
G. tourist
H. ecnerwala

And here is the information from our title sponsor:

Hello, Codeforces!

We, the TON Foundation team, are pleased to support CodeTON Round 8.

The Open Network (TON) is a fully decentralized layer-1 blockchain designed to onboard billions of users to Web3.

Since July 2022, we have been supporting Codeforces as a title sponsor. This round is another way for us to contribute to the development of the community.

The winners of CodeTON Round 8 will receive valuable prizes.

The first 1,023 participants will receive prizes in TON cryptocurrency:

• 1st place: 1,024 TON
• 2–3 places: 512 TON each
• 4–7 places: 256 TON each
• 8–15 places: 128 TON each
• …
• 512–1,023 places: 2 TON each

We wish you good luck at CodeTON Round 8 and hope you enjoy the contest!

Hej, Codeforces!

mesanu, SlavicG and I are very excited to invite you to Codeforces Round 937 (Div. 4)! It starts on Mar/28/2024 17:45 (Moscow time).

The format of the event will be identical to Div. 3 rounds:

• 5-8 tasks;
• ICPC rules with a penalty of 10 minutes for an incorrect submission;
• 12-hour phase of open hacks after the end of the round (hacks do not give additional points)
• after the end of the open hacking phase, all solutions will be tested on the updated set of tests, and the ratings recalculated
• by default, only "trusted" participants are shown in the results table (but the rating will be recalculated for all with initial ratings less than 1400 or you are an unrated participant/newcomer).

We urge participants whose rating is 1400+ not to register new accounts for the purpose of narcissism but to take part unofficially. Please do not spoil the contest for the official participants.

Only trusted participants of the fourth division will be included in the official standings table. This is a forced measure for combating unsporting behavior. To qualify as a trusted participant of the fourth division, you must:

• take part in at least five rated rounds (and solve at least one problem in each of them),
• do not have a point of 1400 or higher in the rating.

Regardless of whether you are a trusted participant of the fourth division or not, if your rating is less than 1400 (or you are a newcomer/unrated), then the round will be rated for you.

Thanks a lot to the testers: erekle, vladmart, nskybytskyi, Vladosiya, KrowSavcik, Dominater069, LucaLucaM, MADE_IN_HEAVEN, tvladm, nor.

We suggest reading all of the problems and hope you will find them interesting. Good luck!

UPD: The round is delayed by 10 minutes: https://mirror.codeforces.com/blog/entry/127616?#comment-1133556.

UPD: The editorial is posted!

Update: TON Tact Smart Challenge #2 has been postponed. More information here.

Please note: CodeTON Round 8 (Div. 1 + Div. 2, Rated, Prizes!) will take place as scheduled. We will be glad to see you among the participants!

Hello, Codeforces!

Have you heard about TON Tact Smart Challenge #2? It's an amazing competition organized by our title sponsor, the TON Foundation in their ecosystem.

This challenge is designed to engage participants in creating a decentralized social network prototype utilizing the Tact smart contract language. The project consists of five stages, each aimed at implementing a core feature of the social network, from user profiles to decentralized management.

We encourage the Codeforces community to participate in this contest. Dive deep into the world of TON Blockchain and explore the limits of what's possible.

Challenge starts on March 25, and lasts until April 3. To enter the challenge, register through @smartchallengebot. You'll receive all the essential details, including start times, submission guidelines, and insights into the challenge stages.

For more information, visit this page.

The scoring system is simple:

Each stage can bring you a max of 6 points. You get 5 points for solving a stage. You get an extra point if you solve it without using any gas.

Minimum amount of points to be eligible for the prize is 6 points.

Prizes:

• $7,000 in TON — The top 15% of eligible participants
• $7,000 in TON — The middle 30% of eligible participants
• $6,000 in TON — The bottom 55% of eligible participants

Impressive, right? Hurry up and join!

Good luck!

The European Championship 2024 will take place on the 24th of March in Prague. The top teams from the European ICPC regionals CERC, NWERC, SEERC, SWERC will compete for the title of European champions. It is the first edition of this ICPC super-regional.

The mirror contest European Championship 2024 - Online Mirror (Unrated, ICPC Rules, Teams Preferred) will be held on Codeforces at Mar/24/2024 13:00 (Moscow time) and will last 5 hours.

The mirror contest will contain the same problems as the official competition.

I am the chief judge for the competition and I want to thank:

• The amazing set of judges who proposed and prepared the problems: antontrygubO_o, bicsi, Giove, Martin Kacer, MZuenni, Petr.
• Our beloved tester ksun48 who showed us that our perception of the difficulties was not exactly spot on...
• Our beloved proofreader Philae for proofreading the statements.
• Everyone involved in the organization of EUC. In particular our director Boba Mannová, and Fernando Silva, Václav Herman, Ondřej Votava, Jan Kubr, Jan Baier.
• The developers of DOMjudge, the contest system used in the official contest.
• MikeMirzayanov for Polygon (that we used to prepare the problems) and for letting us host the mirror on Codeforces.

I invite you to participate in the contest and I hope that you will like the problems.

On the difficulty
The contest features problems with difficulties from div1A to div1E. It should be enjoyable for many, and challenging even for the strongest teams in the world.

Rules

1. The contest is unrated, so your codeforces rating will not be affected.
2. The scoring is ICPC-style: teams are first sorted by number of problems solved, then the time-penalty is used as a tie-break. An incorrect submission gives a 20 minutes penalty.
3. We encourage participation as a team.
4. If you are participating in a team, we encourage you to use only one computer for coding the solutions (as in an ICPC contest). Regarding using templates, googling, and copy-pasting code: feel free to do it.

UPDATE: We hope you liked the problems!

Congratulations to the winners, and especially to the first two teams for AK:

1. dw my perception of the difficulties was not exactly spot on: tourist, ecnerwala.
2. xinyoudui: PubabaOnO, orzdevinwang, jqdai0815
3. MIPT: Yolki-palki: Tikhon228, Pechalka, Kapt
4. Captain take me!: crazy_sea, A_zjzj, 275307894a
5. Beyond Three Wolves: Kevin114514, CrTsIr, Atomic-Jellyfish
6. HSE: FFTilted: Kirill22, Ormlis

We uploaded the editorial of the contest.

Tune in to ICPCLive to see the closing ceremony and find out how the onsite teams did at 18:00 CET!

UPDATE 2:

Congratulations to the medalists of the onsite contest:

1. Warsaw Eagles 2024 — University of Warsaw (the only team with 9 problems)
2. Zagreb 1 — University of Zagreb
3. KNU_0_GB_RAM — Taras Shevchenko National University of Kyiv
4. ELTE 1 — Eötvös Loránd University
5. UWr 1 — University of Wroclaw
6. ENS Ulm 1 — École Normale Supérieure de Paris