Hello Codeforces!

We are glad to invite you to the upcoming Codeforces Round #618, which will start at Feb/09/2020 17:05 (Moscow time).

Each division will consist of 5 problems and will have 2 hours to solve the problems. There will be an interactive problem in the round. Learn more about them here.

This round was prepared by rotavirus, rotavirus, rotavirus, rotavirus, antontrygubO_o and nvmdava. We would like to thank MetB, stefdasca, cfalas, gamegame, hugopm, Redux, dorijanlendvaj, imbr92, CP_Sucks, 300iq, Rahul, AryaKnight, 244mhq, manish.17, Um_nik, mblazev, pseudocoder10, aryanc403, box for testing and their invaluable feedbacks. And special thanks to MikeMirzayanov for making this round possible and antontrygubO_o for coordination of the round.

We hope that you will enjoy the problems we've set, and wish you good luck and a high rating.

Upd 1. Some of us might be online at AC discord server after the round ends.

Upd 2. Score distribution:

• Div2: 500 750 1250 1750 2000
• Div1: 500 1000 1250 1750 2250

The contest is over. Congratulations to the winners.

Div1:
1. jqdai0815
2. TLE
3. Radewoosh
4. zhouyuyang
5. Benq

Div2:
1. ntftxdy
2. qsmcgogo
3. ZhouShang0817
4. sarthakmanna
5. nantfaker

Editorial

Hi Codeforces!

The platform recently turned 10 years old. We accept your congratulations at https://codeforces.com/10years. Please review the progress in 2019 and support the anniversary crowdfunding campaign. Your donation will be a contribution to the future of Codeforces, will help its development and work. We need resources to continue to host rounds, not to stop developing, to innovate and to maintain the existing infrastructure.

In 2019, together with numerous writers the coordinators worked on problems: KAN, 300iq, cdkrot, arsijo and recently joined isaf27. And this year, rounds coordinated by other experienced members of our community can be expected. Intrigued?

The main innovations in the platform are implemented by me and the developers: kuviman, cannor147 and geranazavr555. Una_Shem provided great organizational assistance. Thanks!

I send special rays of gratitude to problem writers and testers! This year we have had more rounds than ever before!

Time to take stock of 2019.

Partner Events

We are pleased to hold programming competitions with companies or for companies. I'm sure this is a great way to support the community of young programmers and hire talented candidates. Here is a list of our main partners this year:

• Telegram and personally Pavel Durov is supporting Codeforces activities for many years, every regular round is held with their help, thank you!
• Mail.Ru — Technocup and Russian AI Cup
• VK, VK Cup — now a personal multi-track competition for Russian-speaking programmers
• XTX Markets, Codeforces Global Rounds — a series of 6 rounds with a separate scoring and souvenirs for the best participants
• Harbour.Space University — a series of educational rounds, the selection of summer school Tech Scouts
• JetBrains, Kotlin Heroes Rounds — Kotlin programming language contests
• Huawei — research competition (marathon) with elements of machine learning
• Forethought, Forethought Future Cup — a two-level competition with the Final at Forethought headquarters (San Francisco) and the mirror contest for worldwide participants
• Dasha.AI, Dasha Code Championship — a two-level competition with the Final at St. Peterburg and Novosibirsk (and the mirror contest for worldwide participants)
• VeeRoute — research competition (marathon)
• Microsoft, Microsoft Q # Coding Contest — unusual quantum computing competition

Hi Codeforces!

Colleagues from Google asked to share the announcement. Join, it'll be fun!

Hello!

Google’s team programming competition Hash Code is back for another year of challenging developers around the world to solve a Google engineering problem. Think you could optimize the layout of a Google Data Center? Or how about perfecting video streaming on YouTube?

If you’re up for the challenge, sign up to compete by February 17 at g.co/hashcode.

Hash Code takes place over 2 rounds:

• an Online Qualification Round: Thursday, February 20 from 17:30 — 21:30 UTC: Compete from this virtual round wherever you’d like, including from a Hash Code hub. Hubs allow for teams from the same community (e.g. university or coding club) to compete side-by-side in a fun and exciting environment.

• a Final Round at Google Ireland: Saturday, April 25: Top scoring teams from the Online Qualification Round are invited to our Dublin office to vie for cash prizes and the title of Hash Code 2020 champion.

Whether you’ve just started coding or you’ve been participating in programming contests for years, Hash Code is a great chance to flex your coding muscles, get a glimpse into software engineering at Google, and have some fun. Take a look at previous Hash Code problem statements to see the engineering challenges participants have tackled in the past.

Register by Feb 17 at g.co/hashcode

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Hello! Codeforces Round 617 (Div. 3) will start at Feb/04/2020 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 nooinenoojno Stepanova, Mikhail awoo Piklyaev, Maksim Neon Mescheryakov and Ivan BledDest Androsov for help in round preparation and testing the round.

Good luck!

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UPD: Editorial is published!

Hello!

Traditionally AIM Tech organizes a big party for Petrozavodsk camp participants to have fun and get an opportunity to communicate with each other. Usually it comes along with a funny contest in unusual format. This year we decided to share the fun with all codeforces community!

This year we came up with a format requiring (probably) less time for preparing the contest. It is somewhat similar to an ordinary contest with a 3-hour duration. We already have some problem ideas, so it should be super easy to prepare the problems just one night before the competition. We hope everything will run smoothly!

The contest will start on Feb/03/2020 19:15 (Moscow time). It could be a bit rescheduled due to onsite delays.

It will be an unrated funny competition. Unlike usual ICPC-style contests, you'll be given an archive with several open test cases and answers for each problem. You'll have some sample test cases in the statement too, they'll be included in the archive. However, the solutions will be tested against both open and hidden tests. The open tests will be published as an encrypted zip-archive in this post. The password will be published just before the start of the contest.

The statements will be in English only because we are running out of time in preparation and have to prioritize things.

It's not 100-percent clear at the moment, but it seems the contest will be somewhat hard, so we recommend it for div. 1 participants. However, div. 2 participants are welcome as always, but we can't guarantee the contest will be a perfect match for them.

It's possible to participate both individually and in teams of maximum 3 persons.

Another point to mention is that the order of problems could be not the same as the order of their difficulties. But we'll try to do so. A bit.

The authors to blame are Kostroma, zemen, Golovanov399, mathbunnyru and ArtDitel.

As you may notice, it is just one night before the competition, so we should start preparing the problems. We hope that we'll manage not to do very stupid bugs in the tests. See you at the competition!

UPD It's still more than 4 hours before the contest, but the open tests are already prepared! You can download the archive using one of the two links: one two. The encrypted archive contains another archive containing the actual tests.

The password will be published here shortly before the start of the contest.

UPD2 We have to move contest 10 minutes forward, because we need to prepare the last problem :(

UPD3 Oops, the contest is about to start, but we still don't have correct solutions! Unfortunately, each authors' solution contains a bug (or even several bugs!). However, we decided not to cancel the competition. We give you the outputs of the model solutions on open tests in the archive. Guess all the bugs in our solutions and get OK for the code with exactly same bugs! Good luck and have fun!

The password to the archive will be published as a clarification in the contest interface.

UPD4 The password to the archive is oops_seems_that_nobody_tested_the_solutions

UPD5 The editorial is published, but it still does contain bugs, wait a bit while it is being debugged.

UPD6 Feel free to share your opinion in the comments! Were the solutions enough buggy? Was it enough hard, or we should've added a couple of hard problems? Do you want to solve such contests in future?

Hello Codeforces o(≧∇≦o) I'm glad to introduce you to Codeforces Round 616 (Div. 1) and Codeforces Round 616 (Div. 2), which will take place on Feb/02/2020 17:05 (Moscow time).

Each division will contain 6 problems, and you will have 2.5 hours to solve them. There might be interactive problems, feel free to learn about them here. The problems were created by 265918, Ari, Kuroni, gamegame, and hugopm.

Now, here are some people I would love to mention:

• Thank you isaf27 for being a super helpful, diligent, and humorous coordinator ヽ(〃･ω･)ﾉ

• Thanks to McDic, nvmdava, dorijanlendvaj, antontrygubO_o, sdssudhu, and farmersrice for helping with the preparation of the tasks.

• Thanks to Sofie_Ever, mcfr, MathisHammel, thenymphsofdelphi, neko_nyaaaaaaaaaaaaaaaaa, Endagorion, bjn, Capricornmean, xuanquang1999, Jefe, low_, ngkan, pandourson, mth1908, toshinaritong, EPN, zscoder, minhducsun2002, I_love_Michel_Sardou, 300iq, Noam527, AkiLotus, paquechee, and MofK for testing and giving feedback as well as suggestions to the rounds.

• Thanks to MikeMirzayanov for the wonderful Codeforces and Polygon systems that made this contest possible.

The statements were made as clear as possible for your best experiences. Moreover, we sneakily included a theme in the problemset, and each problem will have an easter egg that is the clue to the theme. If you have AC'd every problem, be sure to search for the theme（*´▽｀*)

Additionally, most of us are in a Discord server dedicated to competitive programming called "AC" (this is also the motto of this contest). We will be on the server after the contest to discuss the problems with you. You can find the server here!

I wish you all have good luck and high ratings ( ´ ▽ ` )ﾉ

UPD1: Here is the score distribution:

• Div. 2: 500 1000 1500 2000 2750 3000

• Div. 1: 500 1000 1750 2500 3000 3250

UPD2: Here is the editorial, including easter egg solutions!

UPD3: Thank you everyone for participating :D Here are the final standings:

Div. 1:

1. tourist

2. fateice

3. ksun48

4. Um_nik

5. WZYYN

Div. 2:

1. IZONE

2. Infoshoc

3. CouponKaka-ChutteNahiHai

4. lzh12139

5. liqing

Thank you everyone and I hope to see you again!

Hello Codeforces!

On Jan/29/2020 17:35 (Moscow time) Educational Codeforces Round 81 (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 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 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:

Hi Codeforces!

As a special prize for the Educational Round 81, we would like to invite the top participants to take part in our Hello Muscat ICPC Programming Bootcamp, which will take place in Oman, from March 19 to March 25, 2020. The prize will cover the participation fee, accommodation, and half-board meals for the entire duration of the bootcamp (except flights)!

There are three requirements to satisfy:

• You took part in at least 10 rated contests on Codeforces
• Your max rating should be less than 2400
• You should be eligible for ICPC and/or IOI 2020+

Good luck to everyone!

We are also excited to announce that we are working with our partners to provide free participation (flights not included) for the teams going to the ICPC World Finals 2020, which will take place in Moscow. If you and your team qualified for the Finals, fill out the form below to see if you’re eligible.

Congratulations to the winners:

Congratulations to the best hackers:

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

UPD: Editorial is out

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Hello! Codeforces Round 615 (Div. 3) will start at Jan/22/2020 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 nooinenoojno Stepanova, Mikhail awoo Piklyaev, Maksim Neon Mescheryakov and Ivan BledDest Androsov for help in round preparation and testing the round.

Good luck!

I also would like to say that participants who will submit wrong solutions on purpose and hack them afterwards (example) will not be shown in the hacking leaders table.

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This is unusual, but good news! Our friends at Harbour.Space have a message for you:

Hi Codeforces!

As a special prize for the Codeforces Round #615, we would like to invite the top 3 participants to take part in our Hello Muscat ICPC Programming Bootcamp, which will take place in Oman, from March 19 to March 25, 2020. The prize will cover the participation fee, accommodation, and half-board meals for the entire duration of the bootcamp (except flights)!

There are three requirements to satisfy:

• You took part in at least 10 rated contests on Codeforces
• Your max rating should be less than 1900
• You should be eligible for ICPC and/or IOI 2020+

So unofficial participants are also in a game (if meet the requirements).

Good luck to everyone!

UPD: I want to thank Artem Rox Plotkin and Dmitrii _overrated_ Umnov for invaluable help with the round preparation!

UPD2: Editorial is published!

"Can you hear me?"

"Vanessa...?"

Hello Codeforces!

We are here to invite you to Codeforces Round #614 (Div. 1) and Codeforces Round #614 (Div. 2), which will take place at Jan/19/2020 16:35 (Moscow time). The round is rated for both divisions.

This is our first round including Div.1 parts, hopefully you'll find the problems interesting. ;)

This round is themed based on the Rayark Inc.'s rhythm game, "Cytus II". You are about to help our characters in various problems, whether inside or outside of the virtual Internet! Also, feel free to listen to the music tracks I've chosen from the game for each problem (and later, editorial!). ;)

Each division will be given 6 problems to solve in 2 hours. The round's problems were prepared by Xuan-Quang xuanquang1999 D. Nguyen, Duy-Bach AkiLotus Le and Tuan-Dung low_ To.

Interactive problem(s) might be found in this round. Learn about them here.

We also want to thanks our friends for helping this contest being possible:

• Our dear Codeforces coordinator Dmitry cdkrot Sayutin for reviewing our problems, and roasting a whole bunch of them as well. :D
• Grigory vintage_Vlad_Makeev Reznikov, Quang-Minh MofK D. Nguyen, Yufan ouuan You and Sulfox for helping us in preparing and adjusting difficulties of a few problems.
• Anton antontrygubO_o Trygub, Duc-Trung Kuroni D. Dang and Duy-Thuc leduythuc Le for being our testers.

Last but not least, I want to give a huge appreciation to MikeMirzayanov for the awesome Codeforces and Polygon platform, which makes this contest possible.

Wish everyone good luck and high rating!

UPD1: Editorial is available here.

UPD2: Many more testers helped us in this round! Huge thanks to Kevin ksun48 Sun, Andrew ecnerwala He, Aydar aid Sayranov, Nikolay KAN Kalinin, Oleg Mustang98 Vallas, Mohammed mohammedehab2002 Ehab, Artem Rox Plotkin, Mingming Nero Zhang, Darko Aleksic, Ilya IlyaCk Porublyov, NatInTheHat and NIWIS!

UPD3: Score distribution:

• Div. 1: 500-750-1250-1750-2250-2750
• Div. 2: 500-750-1250-1500-2000-2500

UPD4: True editorial is available here!

UPD5: The contest is over. Thanks for participating, and here are the winners:

• Div. 1:

1. Um_nik (first to solve F)
2. tourist (first to solve A, B, D and E)
3. Benq
4. HIR180
5. jiangly
6. TLE
7. AprilGrimoire
8. Golovanov399
9. cz_xuyixuan
10. fateice

• Div. 2:

1. DestinyFucker9000 (solved all Div.2 problems!)
2. about
3. Isaunoya
4. espr1t
5. Nephren
6. the_happy_camel
7. changruinian2020
8. Agarifighter
9. Small_Pax
10. TaeHo0o00o0N

Also, as the direct setter of Div1B/Div2D, I sincerely apologized for the weak testsets. I must admit, I underperformed this time, and might cause some of you inconvenience. Hope to see you guys another time with a better contest.