Hello Codeforces!

On Apr/09/2022 17:35 (Moscow time) Educational Codeforces Round 126 (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!

UPD: Editorial is out

Dear Codeforces Community,

Kirill22 and I are glad to invite you to Codeforces Round 781 (Div. 2), which will take place on 08.04.2022 17:35 (Московское время). This round will be rated for the participants with rating lower than 2100

These are some great people that we would like to thank:

• Artyom123 for round coordination (and KAN too!) and being in touch all the time for providing help
• Igorbunov, generic_placeholder_name, nskybytskyi, AlperenT, FairyWinx, TheScrasse, Ziware, vsinitsynav, wery0, Kotehok3, YanikusGG, Absyarka, FelixDzerzhinsky, Codula for testing and providing tons of feedback and making completely different submissions
• MikeMirzayanov for Codeforces and Polygon
• NEAR for supporting the Codeforces Community! You can find the details in this post.

You will have 2 hours to solve 5 problems.

One of these problems is interactive, please see the guide of interactive problems if you are not familiar with it.

The scoring distribution: 500 — 750 — 1250 — 1500 — 2250

P.S. I have been waiting for a long time to hold another contest and now this time has come. I really hope that you will like the problems, good luck!

UPD: Editorial

Hello.

I started processing responses on the form where we collected your TON wallet addresses. Unfortunately, many winners did not complete the form. I contacted some of them in PM and it turned out that this was not intentional.

We are extending the deadline for completing the form until 2022-04-06 23:59:59 (UTC +3). Please, if you want to receive coins, then fill out the form. A valid address looks like a random 48-character string. To register a wallet, follow one of these links: https://tonkeeper.com/ or https://wallet.ton.org/

The form can be filled out at https://codeforces.net/userForm/203c74605996e40f

Coins will be received by those who are at the top-1000. Additionally, those who solved at least one problem in this round will receive 1 coin each. Details can be read at the link.

The form will be processed on April 7th. And in a week after it, we will send out coins. Please do not disturb me or the organizers with questions that are answered in this post.

Also I remind you about TON Smart Challenge contest aimed at contract source code optimization: https://t.me/toncontests/26 It's not too late to connect and try your hand

You can read more about this competition here:

With Nickolas not writing a contest this year, magnus.hegdahl and I have decided to take up this sacred duty :). We would like to invite everyone on Codeforces to the April Fools Day Contest 2022. Special thanks to BucketPotato for volunteering to test this contest!

The 10th April Fools Day Contest will take place on Apr/01/2022 17:35 (Moscow time). This is a joke competition in which solving the problem is often easier than figuring out what the actual task is.

In this round you'll be given several weird problems and 2 hours to solve them. The contest will use ACM ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them), and it will be unrated. You can submit solutions in any language allowed by Codeforces, unless the problem says otherwise. To get an idea of what the contest will look like, you can check out the contests of the past years: 2012, 2013, 2014, 2016, 2017, 2018, 2019, 2020, 2021.

Good luck, and have fun!

UPD: There will be 8 problems. There will be only be an interactive problem if the Collatz Conjecture is true...

UPD: Thanks to everyone who participated! I hoped you enjoyed thinking over the problemset. The editorial is available, complete with solution code and hints. Special congratulations to the winners.

Hello! Codeforces Round 780 (Div. 3) will start at Mar/31/2022 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 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 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.

Thanks to NEAR for supporting this round, details can be found in this post.

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 team: MikeMirzayanov, MisterGu, myav, Gol_D, Aris, senjougaharin and Vladosiya.

We would like to thank: arvindr9, hocky, lucasxia01, Evirir, Sorting, 244mhq, yorky, Jostic11, sansen, leaf1415, Masha237, amr_abdelazim, coderbd, gs17005, nebula for testing the contest and valuable feedback. List of testers will be updated.

Good luck!

UPD: Editorial

Hello, Codeforces.

We live in difficult times. And, unfortunately, our community is highly dependent on world events around us. Three years ago, it seemed easy to send a t-shirt anywhere in the world. Now it's a quest with many unknowns. Just a few months ago, it was not difficult to send a reward to the problem writer. But now, we are cut off from the outside world and regulated by multiple new laws.

And here it is very important not to lose, not to break what has already been done. Don't stand still, move forward. I am very glad and grateful to the problem writers and coordinators that in March we managed to hold 10 ratings (we held 9, come to participate in the tenth). Thanks to everyone who took part in the preparation!

And I want to share another great news. Our friends NEAR has come up with the initiative to support the community during this difficult time. We are pleased to announce that the upcoming rounds will be funded by NEAR, which will help with the payment of rewards to problem writers and coordinators. This is a timely and important help. Thanks!

It will be easier and faster for us if the problem writers or coordinators have the opportunity to accept a reward in the form of a cryptocurrency transfer. In this case, we are ready to transfer 25% more and make the transfer much faster. Oh, it's a pity we can't send t-shirts with crypto.

And I remind you that the next round (and Codeforces Round #780 (Div. 3)) is waiting for you) will take place very soon, on Mar/31/2022 17:35 (Moscow time). I hope to see you among the participants.

— Mike

TLTR: If you are in the top-1000 of CodeTON Round 1, then fill out the form by the link https://codeforces.net/userForm/203c74605996e40f. Also, anyone who solved at least one problem in the round can fill out it and get 1 TON airdrop. The deadline is 23:59:59 (UTC +3) 04.04.22.

Hello. Great news from the TON Team. I give them the floor.

Good news everyone!

We decided to celebrate the successful finish of the CodeTON round by airdropping all the people who have solved at least one of the problems (officially, practice and virtual participation don't count) of the CodeTON round. Such participants are eligible for 1 TON airdrop and a memorable NFT. Please do note that such NFT bears only symbolic value and is not entered to have any financial or investment value.

Please submit your TON wallet address via the link https://codeforces.net/userForm/203c74605996e40f if you are eligible for such an airdrop by 23:59:59 (UTC +3) 04.04.22.

Winners are more than welcome to provide organizers with the TON Wallet addresses to claim their prizes.

We also want to invite all of you to try yourself at TON Smart Challenge contest aimed at contract source code optimization: https://t.me/toncontests/26

You can read more about this competition here:

Thank you for taking your part, hope you enjoyed the round, looking forward to meeting you later!

TON Foundation

Xin chào, Codeforces! (Hello, Codeforces!) ٩ (◕‿◕｡) ۶

Me, _FireGhost_ and SPyofgame are glad to invite you to Codeforces Round 779 (Div. 2), which will take place on Mar/27/2022 17:35 (Moscow time). The round will be rated for participants with rating lower than 2100. You will have 2 hours to solve 6 problems, one of which is divided into two subtasks.

In this contest, you will meet Kitagawa Marin and her friends Gojou, Juju and Shinju from My Dress-up Darling! We hope you will find our problems interesting. Good luck to you all! (ﾉ ◕ ヮ ◕) ﾉ *: ･ ﾟ ✧

We sincerely thank the following people for their contributions in the round:

• errorgorn for rejecting 20 problems from SPyofgame coordinating the round and KAN who guided him in his first coordination.

• SPyofgame and myself for setting problems and _FireGhost_, mewnian, _LEOS_, Mondeus for helping us prepare problems.

• antontrygubO_o for providing the idea for one of the problems.

• Kuroni for being the problemsetter team's caretaker the English proofreader.

• _FireGhost_, mewnian, _LEOS_ and SuckTinHock for setting tasks which failed to make the final problemset.

• Monarchuwu for breathing and SPyofgame for being the team's punching sandbag.

• antontrygubO_o, Kuroni, thenymphsofdelphi, darkkcyan, rama_pang, Yurushia, ngpin04, hieplpvip, Pichu, maomao90, FallingStar, Mike4235, Lyde, BaoJiaoPisu, HynDuf, NguyenDangQuan, thanhchauns2, vodacbaoan, hieu_2004, novaland, DMCS, Dirii, welleyth, QuangBuiCPP, Minhho2005, Kriz_Wu, sweet_hope25, kieusontungcva, CrazyDave53, KarD1m, damnson, lk2147, 2qb, OnionEgg for testing the round and providing useful feedback.

• unreal.eugene, geranazavr555 and MikeMirzayanov for Russian translations.

• MikeMirzayanov for great Codeforces and Polygon platforms.

Score distribution: $$$500-1000-1750-(1250+750)-2500-3000$$$

UPD: Editorial

Congrats to the winners:

1. tourist
2. disorientation
3. A-SOUL_Official
4. Geothermal
5. oleh1421

Hello!

It is a pleasure to invite you to CodeTON Round 1 (Div. 1 + Div. 2, Rated, Prizes!)! The round will take place on Mar/24/2022 17:35 (Moscow time). The round will be rated for all participants. The problems of the round were authored by FelixMP, and they were prepared by FelixMP and xpov1LL.

I would like to thank the following people:

• Baqtraqking for having the idea of preparing a Codeforces Round and helping with the solution to one problem; Baqtraqking, izanbf and xpov1LL for early help and discussion of problems, and Baqtraqking, xpov1LL and OneStone for proposals that did not make it to the final problem set.
• 74TrAkToR for coordination of the round.
• MikeMirzayanov for the great platforms Codeforces and Polygon.
• Um_nik, Monogon, AlexLuchianov, generic_placeholder_name, TeaTime, EdgarMM19, cescmentation_folch, metatron, plagues, mathusalen, javierlc2000, DIvanCode, Farrius for testing the round and providing feedback.

There will be 9 problems in the round, with score distribution $$$500 - 1000 - 1500 - 2000 - 2500 - 3000 - 3250 - 3750 - 4500$$$. Hope you have fun!

UPDATE: Editorial.

Here is information from our partners:

Hello, Codeforces!

We, the TON Foundation team, are pleased to support the CodeTON round and invite you to the TON Smart Challenge 1 competition, which will be held on our platform.

The Open Network (TON) is a fully decentralized blockchain created by the Telegram team for a mass audience.

The TON protocol was designed by Nikolai Durov — who is a two-time ICPC world champion, a three-time IMO gold medalist, a multiple IOI medalist, and a co-founder of Telegram — and other winners of international competitions. Now TON is being developed by a community of independent developers and teams.

The winners of CodeTON Round 1 will receive valuable prizes.

The first 1,000 participants will receive prizes in TON cryptocurrency:

• 1st place: 1,000 TON
• 2–3 places: 600 TON each
• 4–10 places: 100 TON each
• 11–100 places: 15 TON each
• 101–1,000 places: 8 TON each

Also, the top 15 participants of CodeTON Round 1 will receive branded hoodies.

In addition, a separate TON Smart Challenge 1 contest will start on our platform on March 28. We invite you to join this competition as well.

You can read more about this competition here:

We believe that the problems of optimizing the efficiency of smart contract code execution on the TON blockchain may be of interest to participants in algorithmic competitions. The development of smart contracts is a case where the experience of optimization earns money by definition because a network fee is paid for each operation on the blockchain.

We wish you good luck at CodeTON Round 1 and hope to see you among the TON Smart Challenge participants!

UPD: If you have got into prizes or just want to join the TON, then register a wallet, follow one of these links: https://tonkeeper.com/ or https://wallet.ton.org/

Hello Codeforces!

On Mar/22/2022 17:45 (Moscow time) Educational Codeforces Round 125 (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!

UPD: Editorial is out.