By SerezhaE, 5 weeks ago, translation, In English,

Hello Codeforces!

We are glad to invite you to the Codeforces Round 586 (Div. 1 + Div. 2). Yes, it is rated!

The problems were invented and prepared by Alexponomarev7, adamant, lesswrong, wrg0ababd, allrats, I_love_QMsh, msmlkm and me, SerezhaE. A lot of thanks to 300iq and _kun_ for help in contest preparation, and also we want to thank MikeMirzayanov for Codeforces and Polygon systems.

The contest starts on Wednesday, September 18 at 16:05 UTC and you will have 2 hours to solve the problemes. I believe everyone will find interesting problem for themselves :)

UPD. Editorial is published!

Good luck!

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By Biza, 5 weeks ago, In English,

Hello, Codeforces!

It's our pleasure to announce the the finals of the 12th Bubble Cup! Bubble Cup is a programming competition organized by Microsoft Development Center Serbia (MDCS). The contest will take place on Saturday, 14th of September at 10:00 UTC+2 in Belgrade, and will last for 5 hours. Live results will be available on the official Bubble Cup website. Results will be frozen during the last hour of the competition. The winners will be announced at the closing ceremony.

The format of the competition is very similar to ACM-ICPC — teams consisting of up to three people are allowed, and they have one computer and five hours to solve problems without partial scoring. Ties are broken using the usual time penalty rules.

Just like in the previous years, there will be an online mirror of the finals here at Codeforces, starting on Sunday, 15th of September at 15:35 UTC+2.

Just like last year, the onsite competition is divided in two "divisions", called Premier League and Rising Stars. The two contests will have most of their problems in common, but the Rising Stars competition will feature some easier tasks targeted at high school contestants. We do not guarantee that every problems unique to Div2 is easier than every problem that is not.

Both of the contests will be mirrored here on Codeforces, with Premier League mapping to the Div1 contest and Rising Stars mapping to the Div2 contest. The mirror will use native Codeforces ACM-ICPC team contest rules.

Both contests will be unrated, due to the format and the length of the mirror being dissimilar to the standard Codeforces rated rounds. Note that this is a team contest, i.e. competing in teams up to three people is allowed. (Of course, you can also compete in a 1-person team.) There will be at least 8 problems in each division.

As of now, Codeforces does not support rating-based divisions in team contests, so we came with the following ad-hoc rule: teams with the maximum rated member having rating less than 1900 should enter the Div2 contest. Teams with the maximum rated member having rating at least 2100 should definitely enter the Div1 contest. The teams not covered by the previous two criteria are free to choose.

Here are the past Bubble Cup mirrors on Codeforces:

Bubble Cup 8 — Finals [Online Mirror]

Bubble Cup 9 — Finals [Online Mirror]

Bubble Cup X — Finals [Online Mirror]

Bubble Cup 11 — Finals [Online Mirror, Div. 1]

Bubble Cup 11 — Finals [Online Mirror, Div. 2]

The problems and their solutions were created by employees and interns of Microsoft Development Center Serbia (MDCS).

We are very grateful to MikeMirzayanov and the rest of the Codeforces team for their support and the wonderful Polygon platform. Special thanks to knightL for big help with problem testing.

The full editorial, together with the statements and solutions of the tasks from the qualification rounds, will be available in the booklet section of the Bubble Cup website on Sunday.

We wish good luck to all participants!


Congratulations to everyone who participated!

Top three teams in Div1 who were also the only teams who solved all 9 problems:

  1. ITMO University: Standard deviation: Nebuchadnezzar, senek_k, _kun_

  2. Almost Retired: KAN, Um_nik

  3. denglaoshi fans: 300iq, wxhtxdy

Winners of Div2 are:

  1. Omar^3: OmarHashim, Momentum, omarosama96 with 5 problems solved

  2. WNTN: Diashka, DeD_TihoN, ZloyHR with 4 problems solved

  3. Reversal Destiny: SorahISA, hq8398 with 4 problems solved

You can now find the solutions to the problems in the booklet section of the Bubble Cup website.

Thanks to everyone who took part in the competition!


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By BledDest, 5 weeks ago, translation, In English,

Hello Codeforces!

Codeforces Round #585 (Div. 2) will be held on Sep/15/2019 13:35 (Moscow time). The round will be rated for Div. 2 contestants. There will be 6 problems for 2 hours. Please, notice that the start time is unusual.

The round will be rated for the participants with rating lower than 2100. The statements will be available in Russian and English.

The round will start 2 hours after the start of the Qualification Stage, so they will finish around same time. That's why we ask the participants of the Quals to stay silent and don't share the statements of the contest with anyone. Unfortunately, we cannot add all the problems from Quals to the round, it will contain only six problems.

The problems were prepared by Alex fcspartakm Frolov and me.

We also would like to express our gratitude to Mike MikeMirzayanov Mirzayanov for the permission to make a mirror and Codeforces and Polygon platforms, Ildar 300iq Gainullin for his help with testing the problems and preparing the round. Also big thanks to the testers: Adilbek adedalic Dalabaev and Roman Roms Glazov.

As usual, the scoring distribution will be announced just before the round.

Good luck!

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By Errichto, 5 weeks ago, In English,

Hey, hi, hello.

Codeforces Round #584 - Dasha Code Championship - Elimination Round (rated, open for everyone, Div. 1 + Div. 2) starts on Sep/14/2019 16:05 (Moscow time) and lasts 2h30m. The score drain will be adjusted for longer contest duration. It's a combined rated round with around eight problems. It is open and it is rated for everybody. Yes, it's rated. There are Dasha t-shirts for top 30 competitors (not counting later-to-be onsite finalists).

As an extra, this is an elimination round for those who live in/near SPb/Novosibirsk. More info about the championship is in the other blog. Thanks to Dasha.AI for making such an event for the community!

Problems are prepared by MikeMirzayanov, FieryPhoenix, dragonslayerintraining and Errichto. One of these setters also created Codeforces, thanks for that! And huge thanks to _kun_ for coordinating the round, to Merkurev, isaf27, KAN and me for testing, and finally to mareksom, Radewoosh and Marcin_smu for some small help.

I wish you more fun than bugs. Enjoy the contest!

PS. I recorded the process of preparing one problem with commentary, will publish it on Youtube after the contest. EDIT:

UPDATE, points: A 500, B 500, C 1250, D 1500, E 1000+1500, F 2500, G 1500+2250, H 4000. There are 8 problems and 2 of them are split into two versions. Good luck!

UPDATE, huge congratulations to winners!

  1. Petr
  2. wxhtxdy
  3. LayCurse
  4. zeliboba
  5. 300iq

I was the author of last two problems: Into Blocks (but thanks for _kun_ for preparing it!) and Walkways, hope you liked them.

UPDATE, editorial is out.

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By Dasha.AI, 7 weeks ago, translation, In English,

Hi Codeforces!

We are pleased to announce the start of registration for Dasha Code Championship! We are Dasha.AI — a conversational AI startup with the huge ambition to use voice AI to pass the Full Turing Test. In a very short time, we managed to assemble a strong team of top specialists — among us there are 4 winners of international mathematics competitions, 16 ICPC participants, and several PhDs and Doctors of Science. Scientific research in the field of AI is led by Alexander Dyakonov — Doctor of Physical and Mathematical Sciences, Professor of Moscow State University, Professor Emeritus of the Russian Academy of Sciences, former Kaggle #1.

Recently we’ve been featured on TechCrunch. Every day we work to bring the future closer.

Examples of calls

Our team has grown and exists in a big part thanks to ICPC, and now we want to start paying tribute to the community by holding regular prize championships.

Dasha Code Championship

Dasha Code Championship will be held in two stages — Elimination and Final. The Final will be held simultaneously in two locations — St. Petersburg and Novosibirsk, Russia. According to the results of the Elimination round, lists of finalists in St. Petersburg and Novosibirsk will be formed. Top competitors will be invited to the finals according to the results of the Elimination round and based on their location and ability to travel. The winners of the onsite final (separately to each city) will be awarded the following prizes:

  • I place — iPhone X or 70000 RUR
  • II place — iPad 2018 or 25000 RUR
  • III place — Headphones Jabra Move or 10000 RUR
  • all onsite finalists will receive a signature Dasha T-shirt

Register Now →
Round 1 (Elimination Internet Round)

The open Elimination Internet Round starts on September 14, 2019 at 16:05 (MSK). The round will be rated, open to all members of the Codeforces community. Top 30 competitors will receive official Dasha t-shirts!

Round 2 (Onsite Final Round)

The Onsite Final Round starts on September 22, 2019 at 12:05 (MSK). The finals will take place at the same time in St. Petersburg (at ITMO) and Novosibirsk (at the Dasha office). The top 50 participants in the Elimination round will be invited to St. Petersburg and Novosibirsk (travel expenses are not covered). The results will be made separate for each of the cities and prizes awarded accordingly. For online participants an open rating round will take place.

About company

We first got the idea in 2016. In 2018, a team of ICPC finalists and semi-finalists was formed and in early 2019, Dasha raised $2M from the RTP Ventures and RTP Global funds (early investors in Yandex). We already have over 18 big clients in the Russian Federation and pilot projects in the USA with Fortune 1000 companies. At the moment, Dasha has made over 4,000,000 phone calls on a number of use cases. Our goal is to create a universal platform for voice AI, which will pass the full Turing test with voice. To do this, we need the best minds on the planet and in our team you will have a chance to fully realize your engineering and scientific potential. You can contribute to the creation of something that will define tomorrow’s world.

You can join our team by filling out the form here (for Russian-speaking participants).

Interested in an internship or a job at Dasha.AI?

Make Science Great Again!

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By JetBrains, 2 months ago, In English,

Hello, Codeforces!

First and foremost, we would like to say a massive thank you to everyone who entered and submitted their answers to the first Kotlin Heroes competition which was held back in May. Congratulations to the top 3 winners Petr, ecnerwala, and abacabadabacaba on their incredible achievement, especially considering they were up against 4,500 other registrants from over 63 countries. We’d also like to give a shout out to tourist for being the only other person, outside of the top 3, to manage to solve every problem set from this round. Well done all of you!

Ready to challenge yourself to do better? The second "Kotlin Heroes" competition will be hosted on the Codeforces platform on the 7th of September, 2019, at 14:35 UTC (17:35 MSK, 07:35 PDT, 22:35 CST). The contest will last 2 hours 30 minutes and will feature a set of problems from simple ones, designed to be solvable by anyone, to hard ones, to make it interesting for seasoned competitive programmers. Top three winners will get prizes of $512, $256, and $128 respectively, top 50 will win a Kotlin Heroes t-shirt and an exclusive Kotlin badge, competitors solving at least one problem will enter into a draw for one of 50 Kotlin Heroes t-shirts.

The round will again be held in accordance with a set of slightly modified ICPC rules:

  • The round is unrated.
  • The contest will have 6-10 problems of various levels of complexity.
  • You are only allowed to use Kotlin to solve these problems.
  • Participants are ranked according to the number of correctly solved problems. Ties are resolved based on the lowest total penalty time for all problems, which is computed as follows. For each solved problem, a penalty is set to the submission time of that problem (the time since the start of the contest). An extra penalty of 10 minutes is added for each failed submission on solved problems (i.e., if you never solve the problem, you will not be penalized for trying that problem). If two participants solved the same number of problems and scored the same penalty, then those of them who had previously made the last successful submission will be given an advantage in the distribution of prizes and gifts.

Registration is already open and available via the link. It will be available until the end of the round.


If you are still new to Kotlin we have prepared a tutorial on competitive programming in Kotlin and a practice round, where you can try to solve a few simple problems in Kotlin. All the solutions are open, which means that you can look at the solution even if you haven't solved the problem yet. The practice round is available by the link.

We wish you luck and hope you enjoy Kotlin.

UPD: Thank you for the participation. The editorials are published.

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Announcement of Kotlin Heroes: Episode 2
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By PikMike, 7 weeks ago, translation, In English,

Hello Codeforces!

On Sep/05/2019 17:35 (Moscow time) Educational Codeforces Round 72 (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 Ne0n25 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:

Hello Codeforces,

Harbour.Space University and UTCC are collaborating to offer graduate students from anywhere in the world a once in a lifetime opportunity: fully funded scholarships for our Masters programs in Bangkok.

These scholarships are designed to completely eliminate the barrier between exceptional talents and sophisticated education: they cover the entire tuition fee as well as the cost of living expenses, and furthermore, they provide the student the valuable experience of both studying and working at Harbour.Space University.

We’re looking for the people who are going to change the world.

If you or someone you know are interested in technology, entrepreneurship, or design, and believe you have what it takes, we want to hear from you!


Congratulations to the winners:

Rank Competitor Problems Solved Penalty
1 Tropical_maid 6 212
2 Return.Hao 6 246
3 xyz100 6 272
4 YangDavid 6 280
5 Lawali 6 300

Congratulations to the best hackers:

Rank Competitor Hack Count
1 VegetableP 116:-14
2 Princ_iple 49:-1
3 racsosabe 42:-1
4 shurongwang 36
5 Megatron_99 29:-1
1432 successful hacks and 1595 unsuccessful hacks were made in total!

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

Problem Competitor Penalty
A xyz100 0:02
B Chereshnya_ 0:06
C Florin29 0:06
D IgorI 0:08
E Aria 0:30
F 2-SAD 0:51

UPD: The editorial is out

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By ch_egor, 7 weeks ago, translation, In English,

Hi everybody!

These days Moscow is conducting the 4th International Olympiad of Metropolises that is an international competition for high school students from biggest cities and capitals all around the world. One of the disciplines of the competition is informatics. Rounds of the competition were prepared by the jury members invited from St. Petersburg, Minsk, Belgrade and Moscow olympiad scientific committee which you may know by Moscow team Olympiad, Open Olympiad in Informatics and Moscow Olympiad for young students (rounds 327, 342, 345, 376, 401, 433, 441, 466, 469, 507, 516, 541, 545, 567).

Scientific Committee of the olympiad consists of: Chmel_Tolstiy, Jelena Hadži-Purić, Elena Andreeva, Zlobober, GlebsHP, andrewzta, meshanya.

The problems were developed by isaf27, _kun_, manoprenko, GoToCoding, ch_egor, gritukan, voidmax, grphil, malcolm under the guidance of GlebsHP and Zlobober.

Problems were adapted for codeforces by V--gLaSsH0ldEr593--V and _kun_, also thanks for MikeMirzayanov for systems codeforces and polygon, which was used to prepare problems of this olympiad. Also, thanks LHiC, voidmax and wrg0ababd for testing!

Good luck and high ratings for everybody!

Round will happen on Sep/04/2019 12:05 (Moscow time) and will last for two and half hours.

The round will consist of 8 problems and will be combined for both divisions. The round is rated for all participants.

P.S. We kindly ask everybody who knows problems of an onsite event not to participate in a round and not to discuss them in public, as this may be a subject for disqualification.

UPD1: Winners!

  1. wxhtxdy
  2. gina0605
  3. grumpy_gordon
  4. Radewoosh
  5. kefaa2
  6. cz_yixuanxu
  7. ko_osaga
  8. mango_lassi
  9. Dreaming_to_be_an_LGM
  10. ksun48

Editorial will be published soon.

UPD2: Editorial

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By Vovuh, history, 7 weeks ago, translation, In English,


Hello! Codeforces Round #582 (Div. 3) will start at Aug/30/2019 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 Mikhail PikMike Piklyaev, Maksim Ne0n25 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.


UPD: Thanks to Artem Rox Plotkin for testing the round!

UPD2: Editorial is published!

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