Hello, Codeforces.

Look what an interesting thing I've been working on the last few days. Now, if a problem uses test cases and its validator is written in the recommended way (using setTestCase), then the example inputs are displayed using different colors.

Just follow the link and see how beautiful it turned out: https://codeforces.net/contest/1714/problems!

So far I have enabled this only for the last few rounds, but if everything works as intended, I will enable it for more rounds.

In order to support this, I had to tinker a lot. I made changes to testlib.h so that the validator can return test markup. Support for this markup required changes in various system services. But I think it's worth it!

The coolest thing is that it was possible to implement all this without changing existing problems. If a validator is used using the setTestCase feature, then this improvement can be applied to this problem.

Of course, it would be cool to have similar highlighting in example outputs as well. And even, say, synchronously highlight an input-output test case pair when hovering over. Unfortunately, standard checkers are often used, in which information about test cases is lost. Perhaps I'll apply some heuristics to make it work in most cases.

Hi Codeforces!

GlowCheese, DeMen100ns, SPyofgame and I are delighted to invite you to participate in Codeforces Round #812 (Div. 2).

• Start time: Aug/06/2022 17:35 (Moscow time)
• Duration: 120 minutes.
• Number of tasks: 6, including at least one interactive problem. Make sure to read this blog and familiarize yourself with these types of problem before the round!

Special thanks to:

• errorgorn for wonderful coordination by rejecting 50+ problems from me, all for a better Codeforces.
• KAN for translating our statements.
• Vip testers: satyam343, tfg.
• The great great coordinators that tested our round: antontrygubO_o, RedMachine-74.
• DeMen100ns for providing amazing problems, which helped us a lot.
• GlowCheese and SPyofgame for their great effort, for pointing out mistakes in the original intended solutions.
• FireGhost and neko_nyaaaaaaaaaaaaaaaaa for spending time helping us while they have to organize VNOI CUP 2022.
• Our testers: thenymphsofdelphi, neko_nyaaaaaaaaaaaaaaaaa, generic_placeholder_name, Andreasyan, PurpleCrayon, tfg, BucketPotato, Vladithur, FireGhost, LetterC67, satyam343, 18o3, 1DWalker, vangtrangtan, haong, Megumin2006, dinhsangBKA, KasenIbaraki, Etherite, nyagami, Hehe, sonoobIdie, hydroshiba, LeCaToX, makyuri.ami.
• MikeMirzayanov for amazing platforms Codeforces and Polygon.
• Last but not least, you for your participation and being WA, then dropping at least one color :P

The score distribution is 500-1000-1750-2000-2500-3000

Hope to see you in final standings!

UPD: We have a small gift for a Vietnamese participant who have the highest score, so if it is you, please DM me after contest. Good luck everybody!

UPD2: Editorial

UPD3: Congratulations to the winners!

Div.2:

1. RGB_ICPC7

2. Xylenox

3. 5cd

4. Jason2022

5. Imot

Div.1 + 2:

1. peti1234

2. A_G

3. kotatsugame

4. jiangly

5. Rubikun

Привет, Codeforces!

В 04.08.2022 17:35 (Московское время) состоится Educational Codeforces Round 133 (рейтинговый для Div. 2).

Продолжается серия образовательных раундов в рамках инициативы Harbour.Space University! Подробности о сотрудничестве Harbour.Space University и Codeforces можно прочитать в посте.

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, Владимир vovuh Петров, Иван BledDest Андросов и Максим Neon Мещеряков. Также большое спасибо Михаилу MikeMirzayanov Мирзаянову за системы Polygon и Codeforces.

Удачи в раунде! Успешных решений!

Также от наших друзей и партнёров из Harbour.Space есть сообщение для вас:

Программа Front-end Development от Harbour.Space — это место, где сталкиваются программирование и креативность. Получите стипендию до 50% и воспользуйтесь этой возможностью, чтобы учиться в Барселоне у отраслевых экспертов, пока вы сами становитесь таковым.

Программа в значительной степени ориентирована на развитие профессиональных навыков, необходимых для трудоустройства, и в то же время на развитие умения адаптироваться к быстро меняющимся технологиям.

Итак, давайте познакомимся с руководителями программы:

Hjörtur является генеральным директором 14islands, студии дизайна и развития из Стокгольма в Швеции и Флорипа в Бразилии. Он был соучредителем студии в 2011 году, и с тех пор они работали с такими компаниями, как Google, Adidas, Disney, Facebook, HBO, Shopify, Ericsson и многими инновационными стартапами в мире.

Marco Barbosa является управляющим директором 14islands, студии дизайна и развития из Стокгольма в Швеции и Флорипа в Бразилии. Их проекты получили множество наград, таких как FWA, Awwwards, CSS Design Awards и European Design Awards.

Удачи в раунде,

Harbour.Space University Team

UPD: Разбор опубликован

Hello, Codeforces!

Take a look on excellent news from TON Foundation about TON Smart Challenge.

Please note that this contest will not take place on Codeforces. It is about smart-contracts, not traditional algorithmic problems. But in the last similar competition, the competitive programmers were among the winners!

I pass the floor to the TON team.

The next edition of the TON Smart Challenge contest for programmers is slated to begin on Aug. 4 with a total prize pool of 16,000 Toncoin.

TON Foundation developers have carefully reviewed and considered feedback from participants of the first TON Smart Challenge and will make quality-of-life improvements for the upcoming second part of the competition.

The TON Smart Challenge #2 is aimed at developers just starting their journey of learning FunC, the primary programming language for The Open Network blockchain, and will comprise five simple tasks, which will be checked automatically.

To participate, you must register by going to this website.

You can find more details and news on the competition on the TON Contests Telegram channel.

You can prepare for the competition by studying the documentation section and creating a developer’s environment.

Hurry up, don't miss your chance!

Привет! В 01.08.2022 17:35 (Московское время) начнётся Codeforces Round 811 (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 (и последующих Div. 3 раундах) 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.

Спасибо MikeMirzayanov за платформы, помощь с идеями для задач и координацией нашей работы. Задачи были придуманы и написаны командой Университета ИТМО: MikeMirzayanov, myav, Gol_D, Aris, senjougaharin, мной Vladosiya.

Также большое спасибо yorky, Jostic11, turmax, oversolver, ivanz, antonis.white, molney, KerakTelor, andrey.starodubtsev, Ahmad45123, myway, sofiaasta, Muhammad98 за тестирование раунда и весьма полезные замечания.

Всем удачи!

UPD: Разбор

Hello, Codeforces!

A wonderful summer holiday! After College Entrance Examination, we are extremely delighted to invite you to our second round, CodeTON Round 2 (Div. 1 + Div. 2, Rated, Prizes!), which will be held on Jul/31/2022 17:05 (Moscow time). Note the unusual start time of the round.You are given 8 problems and 2.5 hours to solve them.

All problems were written and prepared by Cirno_9baka, CoupDeGrace, Sugar_fan, ODT, Yakumo_Ran, farmerj, MagicalFlower, izlyforever, kuangbin, mejiamejia, ugly2333 and me.

Task statements and editorials will also be available in Chinese (Simplified) and Chinese (Traditional) after the contest.

We are sincerely thankful for the help provided by:

• 3.141592653, emorgan, errorgorn, SevenDawns, prabowo, why_no_girlfriend, ntherner, arvindr9, ExplodingFreeze, Huah, chenkuowen, plagues, antontrygubO_o, lych123, YunQian, magnus.hegdahl, Bench0310, Roundgod, njupt_lyy, null_awe, aniervs, Savior-of-Cross, dorijanlendvaj, Suiseiseki, dannyboy20031204, Lucina, ChthollyNotaSeniorious, JianfengZhu, aaaaawa, leukocyte, RiverHamster, -skyline-, Nanako, Nezzar, I.Gleb, glebustim, Y25t, gisp_zjz, Mitsukasa_Ayase, ustze, Vladithur, IIIIndex, Acfboy, 127.0.0.1, tibinyte2006, i_wyxkk_ak, TML104, spookywooky, 4qqqq, CSP_Sept, marzipan, efimovpaul, Erkhemkhuu, ak2006, NeuraXmy, RomkaRS, bpaT_Kapaca, sus, snowysecret, 755352046, IgorI, and Kieray for testing and good advice

• RedMachine-74 for his excellent round coordination and help with preparation

• MikeMirzayanov for great systems Codeforces and Polygon

• MinakoKojima, Ynoi, Suiseiseki for proposing problems that didn't been used in the final version of the round.

• Nanako, absi2011, Nezzar, QAQAutoMaton, rgnerdplayer for helping prepare the problems.

• magnus.hegdahl for strengthening the data of one problem (but because the problem was too hard, we removed it)

• emorgan for reviewing the statements

• dannyboy20031204 for traditional chinese statement and editorial

• You, for participating!

This is our second round! Great efforts have been put in during the past year. We are sincerely looking forward to your participation and we hope everyone will enjoy it. Besides, this round is sponsored, which indicates that everyone has an opportunity to get the prize!

Good luck!

UPD1: Here is the score distribution:

500-750-1250-1750-2000-2750-3500-(2250+2750)

UPD2:Tutorial is available.

UPD3: Simplified Chinese tutorial is available.

UPD4: Traditional Chinese tutorial is available.

UPD5: Congratulations to the winners

1. tourist
2. jiangly
3. ksun48
4. heuristica
5. djq_cpp
6. maroonrk
7. cnnfls_csy
8. he_____hezhou
9. 353cerega
10. WYZFL
11. ecnerwala

UPD6: Simplified Chinese statement is available.(please download it and open it with edge)

And here is the information from our title sponsor:

Hello, Codeforces!

We, the TON Foundation team, are pleased to support CodeTON Round 2.

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

Since July, 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 2 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 2 and hope you enjoy the contest!

Hello, Codeforces.

I have wanted for a long time and now, finally, I sat down and did it.

Many of you are familiar with my Testlib project. This is a library that helps you develop problems if you are using C++. In the case of problems for Codeforces rounds, its use is mandatory. It seems to me that it is almost a de facto standard for preparing materials for completely different olympiads and competitions.

The history of С++-Testlib is almost lost in centuries, I published the first version in 2005.

Nowadays, making edits to Testlib has become tricky. The code grown to thousands of lines, also it has too long a history. This increases the likelihood of accidentally changing some aspect of behavior, which will jeopardize the holding of a Codeforces round or another important competition. In short, making a bug in this code or changing behavior anywhere is highly discouraged.

So I recently took the plunge and wrote some tests for Testlib. Here's what tests can do now:

• check that all cpp files in the repository are compiled (test test-000_compile-all-cpp)
• check the plausibility of the behavior of a simple sval.cpp validator on a series of files (test-001_run-sval test)
• check the plausibility of the behavior of the two checkers fcmp.cpp and wcmp.cpp on a series of files (test test-002_run-fcmp-wcmp)
• check that the behavior of the random number generator has not changed (test test-003_run-rnd)
• check the behavior of some functions and the behavior of InStream and opt in a series of unit tests (test test-004_use-test.h)

More good news. All this was automated through GitHub Actions. Tests are automatically run on any push or pull request.

I am the coordinator of Round #810. I will be brief and clear.

The div1E problem was copied by one of the two authors, it was not a coincidence.

For this reason, the div1 part of the round is unrated. Div2 stays rated.

Sometimes known problems appear in a contest, it happened to me as an author and to any problem setter who has organized many contests. This is never a reason to make a round unrated. Today something different happened, the problem was deliberately copied and the author did not tell anything to anybody (not even to the other author). Codeforces (and me personally) condemns this behavior.

A final personal remark: I feel sad. Please future authors: do not copy problems. It's a waste of everyone's time.

Hello Codeforces!

We are glad to invite you to our Codeforces Round Codeforces Round 810 (Div. 1) and Codeforces Round 810 (Div. 2) which will be held on Jul/24/2022 17:35 (Moscow time). This round will be rated for participants of both divisions. Participants in each division will be offered 5 problems and 2 hours to solve them. The two divisions will share 3 problems.

The problems are prepared by me and zxyoi. We hope that everyone will enjoy this round!

We are sincerely thankful for the help provided by:

• dario2994 for his marvelous coordination of this round,

• wyyxhjth for providing feedback on our early ideas,

• flukehn,FairyWinx,Pinkyhead,Vladithur,naman1601,dorijanlendvaj,c337134154,STommydx,LeoRiether,hxu10,Warriors_fsy,idxcalcal,jiaangk_,yakamoto,kiwiHM,Joyemang,forxen for testing our round and giving detailed feedback,

• FairyWinx for finding that one of our problems is coincident with a well-known problem (We replaced it),

• Vladithur for polishing our statements,

• KAN for his great help to our round,

• MikeMirzayanov for the amazing Codeforces and Polygon platforms!

We tried our best to have detailed, clear, and short statements. I think that anyone can find some interesting problems in this contest. We suggest to read all the statements.

The score distribution will be announced later.

Wish you good luck and high rating!

UPD

For some reason, we have removed one of our problems. So now participants in each division will be offered 5 problems and 2 hours to solve them.

The score distribution is:

Div2: $$$500-1000-1500-2000-3000$$$

Div1: $$$500-1000-1750-2000-2750$$$

We have some more testers now, let's thank them!

UPD2

We adjusted our score distribution slightly.

UPD3: the Div. 1 part of the round is declared unrated.

UPD4

Sorry for the late editorial.

UPD5

Congratulate to winners:

Div1

1. nantf

2. ko_osaga

3. Rebelz

4. The_Noble_Brahman_Bison

5. VivaciousAubergine

Div2

1. csyakuoi

2. Linkus

3. yaoxi

4. RGB_ICPC1

5. bajablast

Hi. I'm organizing an online IOI-preparation camp in collaboration with Huawei. Every day will be a 5-hour virtual contest, then my problem analysis, and sometimes a lecture. There will be at least 4 contests and 2 lectures.

We will do some old IOI contests (2013?) from the IOI archive, CEOI (2015-2016?), or maybe JOI/JOISC — to be decided this weekend. I don't want to do recent years like 2021 because most participants already covered it. The example lecture topics are those from Range Queries or Trees in Usaco Guide Platinum.

The camp is free for IOI 2022 participants. For everybody else, the video recordings will be posted on Youtube after the camp. By participating you get the live experience (Discord, asking questions, competing with others, leaderboards).

Dates: 25.07-2.08 (updated)
Time of every analysis/lecture: 14:00 UTC / 16:00 CEST
Price: free for IOI participants, 40 USD for everybody else
Platform: Discord & Codeforces & uj.oz (?)

Big thanks to Huawei UK R&D for sponsoring this camp.

EDIT: I'm now aware of CEOI collision. There's nothing I can do about it :(

Schedule:
25.07 — CEOI 2016 day 1
26.07 — CEOI 2022 day 1 + lecture
27.07 — CEOI 2016 day 2
28.07 — CEOI 2022 day 2
29.07 — lecture + homework
weekend off
1.08 — CEOI 2017 day 1
2.08 — CEOI 2017 day 2

Participants voted to cover CEOI instead of IOI to avoid problems that they already know.