Hello, Codeforces!

We are proud to finally invite you to participate in Codeforces Round #815 (Div. 2), which will start on Aug/18/2022 16:35 (Moscow time). You will be given 5 problems, one of which contains a subtask and 2 hours to solve them. We greatly encourage you to read all the problems.

Round is completely set by SIS (Summer Informatics School) students. During the camp our students did their best to prepare interesting and creative problems. You can check previous rounds prepared by SIS students: Codeforces Round #612, Codeforces Round #530, Codeforces Round #694.

People who participated in the creation of the round:

• Problems are authored and prepared by: Kirill kirill.kligunov Kligunov, Gleb glebustim Ustimenko, Alexey daubi Vasiliev, Stanislav Death_on_2_Legs Alekseev, Vladimir plagues Gerasikov, Artem artem3605 Abaturov, Artem a.stepanov281005 Stepanov, Evgenii pakhomovee Pakhomov, Viktor robivirt Krivoschekov under the guidance of Mikhail meshanya Pyaderkin, Nikolay budalnik Budin, Philipp philmol Molodcov, Vladimir TeaTime Novikov, Fedor fastmath Ushakov.

• Special thanks for testing to: Dmitry Sweezy Pugachev, Alexey Mangooste Mikhnenko.

• And of course we want to thank our army of testers: alexxela12345, wabadabakalakaboo, fishy15, Kapt, rafaelka, alexchist, bashkort, Obeziana_Banana_Clown, Viktoriuss, PUFL, hoshiii, Vladosiya, anporf, elizazh.

• Coordinator: Artyom123

Also, we would like to thank:

• Artyom123 for the brilliant coordination.
• fastmath for improving one of the tasks!
• meshanya for improving the structure of the contest!
• MikeMirzayanov for great platforms, Codeforces and Polygon!

Scoring distribution: $$$500-1000-1250-(1500-1000)-2750$$$.

Good luck & have fun!

UPD1: Editorial

UPD2: Winners!

Div 2:

• Akemi-Homura
• First_Brave_Niuniu
• csyakuoi
• newbie__wrz
• sdfzzsy

Div 1:

• XiaoHa19672364
• -is-this-fft-
• Golovanov399
• Koosha_Mv
• Geothermal

Hello, Codeforces!

SomethingNew and I are glad to invite you to Codeforces Round 814 (Div. 1) and Codeforces Round 814 (Div. 2), which will take place on Aug/16/2022 17:35 (Moscow time). Each division will have 6 problems and 2 hours to solve them.

We would like to thank:

• 74TrAkToR for excellent coordination and for the idea of a problem for Div. 2.
• pakhomovee for idea and preparation of one of the problems for Div. 1, and for testing other problems of the contest.
• Um_nik, 244mhq, turmax, fedoseev.timofey, errorgorn, FairyWinx, daubi, arbuzick, AlesyaIvanova, Dart-Xeyter, Alexdat2000, Vladithur, rafaelka, plagues, LeoRiether, satyam343, ilya.kligunov, 1024mb, 127.0.0.1, efimovpaul, Prokhor08, marzipan, kirill.kligunov, MirMak, dmitry.lisitsyn, MichsSS, PUFL, bpaT_Kapaca, RomkaRS for testing the round and providing useful feedback.
• MikeMirzayanov for Codeforces and Polygon systems.
• ilaburkov for existing.

Score distribution:

Div. 2: 500 — 1000 — 1250 — (1250 — 1000) — 2500 — 2500

Div. 1: (500 — 500) — 1250 — 1250 — 2250 — 2250 — 2750

We hope that you will enjoy solving our problems!

Editorial

Congratulations to the winners!

Div. 2:

1. billieeyelash
2. randboy
3. TasselFlower
4. AVRush
5. Shiroqwq_

Div. 1:

1. tourist
2. maroonrk
3. Petr
4. ksun48
5. Radewoosh

Hi, Codeforces!

Igorfardoc and I are pleased to invite you to our Codeforces Round 813 (Div. 2), which will be held on Aug/13/2022 17:35 (Moscow time). This round will be rated for participants with rating lower than 2100.

We would like to thank:

• DishonoredRighteous for coordinating the round.
• Um_nik, Ormlis, errorgorn, FairyWinx, golikovnik, 74TrAkToR, thenymphsofdelphi, plagues, Kon567889, AlperenT, Alexdat2000, MagentaCobra, welleyth, GlowCheese, satyam343, thanhchauns2, SlavicG, _Vanilla_, jampm, QuangBuiCPP, LeCaToX for testing the round and providing useful feedback.
• MikeMirzayanov for Codeforces and Polygon.

You will be served 6 problems, one of which is divided into two subtasks, and you will have 2 hours and 15 minutes to sample them.

Hope you don't choke 😋

The score distribution is 500 — 1000 — 1500 — 2000 — (2000 — 750) — 3500

UPD: Tutorial

UPD2: Congratulations to the winners!

Div. 2:

1. iztrax
2. TrungNotChung
3. Akemi-Homura
4. bajablast
5. __NONE__

Div. 1:

1. tourist
2. m_99
3. jiangly
4. LJC00118
5. sjc061031

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.com/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, 74TrAkToR.
• 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, QuangBuiCPP, 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

Hello Codeforces!

On Aug/04/2022 17:35 (Moscow time) Educational Codeforces Round 133 (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 Adilbek adedalic Dalabaev, Vladimir vovuh Petrov, Ivan BledDest Androsov, Maksim Neon Mescheryakov and me. Also huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Good luck to all the participants!

Our friends at Harbour.Space also have a message for you:

Harbour.Space's Front-end Development programme is where programming and creativity collide. Receive up to a 50% scholarship and take advantage of this opportunity to study in Barcelona and learn from industry experts while you become one yourself.

The programme is heavily geared towards developing students’ professional skills needed for employment while being able to adapt to rapidly changing technology.

So let's meet your programme leaders:

Hjörtur is the CEO of 14islands, a design and development studio from Stockholm in Sweden and Floripa in Brazil. He co-founded the studio in 2011 and since then they've done work with companies such as Google, Adidas, Disney, Facebook, HBO, Shopify, Ericsson and many innovative startups in the world.

Marco Barbosa is the Managing Director of 14islands, a design and development studio from Stockholm in Sweden and Floripa in Brazil. Their projects have won multiple awards such as the FWA, Awwwards, CSS Design Awards, and European Design Awards.

Good luck,

Harbour.Space University Team

UPD: Editorial is out

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!

Hello! Codeforces Round 811 (Div. 3) will start at Aug/01/2022 17:35 (Moscow time). You will be offered 6-8 problems 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 a rating of 1600 or higher, can register for the round unofficially.

The round will be hosted by rules of educational rounds (extended ACM-ICPC). Thus, solutions will be judged on preliminary tests during the round, and after the round, it will be a 12-hour phase of open hacks.

You will be given 6-8 problems and 2 hours and 15 minutes 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 participant of the third 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 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 our work. Problems have been created and written by ITMO University teams: MikeMirzayanov, myav, Gol_D, Aris, senjougaharin, me Vladosiya.

Also many thanks to yorky, Jostic11, turmax, oversolver, ivanz, antonis.white, molney, KerakTelor, andrey.starodubtsev, Ahmad45123, myway, sofiaasta, Muhammad98 for testing the contest and valuable feedback.

Good luck!

UPD: Editorial

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, valeriu, 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, tibinyte, 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

• 74TrAkToR 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. Rewinding
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.