Hello Codeforces!

On Mar/09/2020 17:35 (Moscow time) Educational Codeforces Round 83 (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 7 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!

Congratulations to the winners:

Congratulations to the best hackers:

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

UPD: Editorial is out

Hello!

Right now happens the first tour of the Open Olympiad in Informatics, and tomorrow will be the second one. This contest is prepared by Moscow Olympiad Scientific Committee that you may know by Moscow Team Olympiad, Moscow Olympiad for Young Students and Metropolises Olympiad (rounds 327, 342, 345, 376, 401, 433, 441, 466, 469, 507, 516, 541, 545, 567, 583, 594, 622).

Open Olympiad consists of the most interesting and hard problems that are proposed by a wide community of authors, so we decided to conduct a Codeforces regular round based on it, which will happen on Mar/07/2020 12:35 (Moscow time) and will be based on both days of the Olympiad. Each division will have 6 problems and 2 hours to solve them.

We kindly ask all the community members that are going to participate in the competition to show sportsmanship by not trying to cheat in any manner, in particular, by trying to figure out problem statements from the onsite participants. If you end up knowing some of the problems of Moscow Open Olympiad (by participating in it, from some of the onsite contestants or in any other way), please do not participate in the round. We also ask onsite contestants to not discuss problems in public. Failure to comply with any of the rules above may result in a disqualification.

Problems of this competition were prepared by meshanya, cdkrot, wrg0ababd, vintage_Vlad_Makeev, DebNatkh, diko, voidmax, okwedook, ch_egor, V--o_o--V, Sender, grphil, mingaleg, KiKoS, Endagorion, budalnik guided by cdkrot, ch_egor, vintage_Vlad_Makeev, GlebsHP, Zlobober and Helen Andreeva.

Problems for second division were prepared by vintage_Vlad_Makeev, ch_egor and MikeMirzayanov, to who we also want to say thanks for the Codeforces and Polygon systems.

Good luck everybody!

UPD1:

The scoring distribution for both divisions is standard: 500 — 1000 — 1500 — 2000 — 2500 — 3000

Due to the official competition source codes of other participants will not be available for an hour after the end of the round.

UPD2: Editorial

UPD3: Winners!

Div. 1:

1. zhouyuyang
2. Egor
3. Rewinding
4. mayaohua2003
5. gtrhetr

Div. 2:

1. Tutituti
2. autoint
3. Froggay
4. WWLDX
5. GMaster

Hello Codeforces!

You may know that the crowdfunding campaign on the occasion of the 10th anniversary of Codeforces is in full swing! I am pleased to inform you that the Reply Code Challenge not only prepare a great competition but also supported Codeforces, which means all of us! Thanks!

Please pay attention to the information below. I am sure that this is a great chance to compete.

And here is the message from the Reply Code Challenge:

Hello Codeforces!

We're glad to invite you to the upcoming Reply Code Challenge, on 12 March. It's a free online team-based challenge and you can choose between:

• Standard Edition: designed for university students and professionals.
• Teen Edition: designed for students aged 14 to 19.

Great prizes are waiting for the winning teams:

• Standard Edition: each member of the winning team will win a Mac Book Pro™ 16’’. Each member of the second and third place team will receive Apple Watch Series 5™ and Apple Air-pods Pro™
• Teen Edition: 5.000€ for the first team in the leader board, 2.000€ for the second and 1.000€ for the third place team.

When&Where?

Online at challenges.reply.com on March 12th from 4.30pm to 8.30pm CET. To play you must form a team by March 11th.

Follow us on our Telegram Channel, WIP but ready soon for the Challenge: https://t.me/replychallenges

The X BSUIR Open Programming Championship will be held from March 21 till May 7, 2020 (Minsk, Belarus).

Semifinal is over, upsolving is open and standings are unfreezed. Thanks to the problemsetters: aropan, teleport, wilcot, Qwertenx, rui-de, Vladik, netman.

Results here: students и school.

UPD3: Registration deadline comes in 30 hours.

UPD: Telegram channel. There's a link there to a chat, where you can talk to other participants and team up.

UPD2: With respect to the situation in the world, organizing committee decided to make online second qualifying for all teams. Registration deadline is extended to April 6 (included). First qualifying round, which is required only for the teams from BSUIR and schools, is also extended to April 6.

Hello Codeforces!

We are thrilled to invite you to CodeCraft-20 (Div. 2), which is to take place on Mar/04/2020 17:35 (Moscow time). The contest is rated for all participants with ratings under 2100.

The contest comes under the wing of Threads '20, the annual technical fest, a part of Felicity, IIIT Hyderabad .

Participants will be asked to solve 6 problems in 2 hours . Scoring will be announced just before the contest .

The problems were created by gaurav172, lazyneuron, preet_t and shaanknight .

We want to thank all the people for making this contest possible .

• Our Coordinator antontrygubO_o for the immense help and guidance.
• All the testers of the round : codelegend, aryanc403, _overrated_, Savior-of-Cross, nvmdava, Rahul, sigma_g, pllk, vivace_jr, hoke_t, pajenegod, Arpanet, suzaku_kuru, heisenberg97, TselmegKh, swetanjal, MohamedMagdy.
• coder_h, riz_1_, night_fury208, firebolt, Altitude, matcoder for help in the problem preparation.
• AnimeshSinha1309, madlad, pk1210 for contributing to the initital set of ideas for the problems .
• Ashishgup for pushing our contest in front of the Codeforces coordinators .
• And finally, MikeMirzayanov for the great platforms, Codeforces and Polygon.

Wish you luck and hope you like the problems !!

UPD 1:

Score-Distribution

500-1000-1500-1750-2250-2500

UPD 2:

Congratulations to the winners of the round.

Div 1

1. tmwilliamlin168
2. 244mhq
3. natsugiri
4. Golovanov399
5. Egor

Div 2

1. Afterglow
2. Zetro
3. I-Love-Islam
4. DraqonLore
5. ix35

UPD 3:

Editorial

Hello Codeforces!

We are glad to invite you to the upcoming “Ozon Tech Challenge 2020”, which will start at Mar/03/2020 17:35 (Moscow time). The round will be open and rated for everybody!

This round is initiated and supported by Ozon.

Ozon — one of the leading players in e-commerce (provides its customers with over 2.5 million product names in 24 categories), a tech company that actively developing its IT department. They already have the largest Golang team in Russia, a proprietary WMS fulfillment management system completely written by the Ozon team, 250 million lines of logs per day, collected on the site and in the Ozon mobile application. Ozon experts perform at the leading profile conferences GoperCon, Heisenbug, GoWayFest, GolangConf, and also at the company site meetups are held for the IT community.

The company shows great interest in the support of the developer community — for schoolchildren there is Ozon Academy, for the older audience there is an internship program Ozon Tech Camp and training program Ozon Masters.

Participants will be asked to solve 8 problems in 2 hours 15 minutes. Scoring will be announced a bit later.

The problems were created by AkiLotus, Ari, Kuroni, zscoder, xuanquang1999, and antontrygubO_o

We would like to thank:

• JettyOller, gamegame, hugopm, dorijanlendvaj, ngfam, ngkan, and 265918 for helping with the preparation of the tasks.
• ecnerwala, 300iq, puppies_and_rainbows, benson1029, entropy07, victoralm, Mbfibat, SeehtEntity, tmwilliamlin168, McDic, pajenegod, leduythuc, enoone, all_too_well, manish.17, aryanc403, hetp111, God_Ra, ScarletS, TselmegKh, cfalas, omgursocute, Redux, and BencilSharpeniro for testing and giving feedback as well as suggestions to the rounds.
• MikeMirzayanov for the wonderful Codeforces and Polygon systems that made this contest possible.

Thanks to Ozon for the gifts to the participants:

• top 10 participants will receive stylish branded backpacks and branded T-shirts;
• 11-20th participants will receive compact portable chargers for 10000 mAh and branded T-shirts;
• 21-60th participants will get branded t-shirts;
• another 30 T-shirts will be played among the rest of the participants, who solved at least two problems, randomly.

We hope everyone will find an interesting problem for themselves. Wish everyone a successful round and high ratings! Good luck!

UPD1:

Score distribution:

500 — 1000 — 1250 — 1750 — 2000 — 2500 — 3250 — 4000

UPD2: Editorial

UPD3: Congratulation to the winners!

1. tourist
2. maroonrk
3. VivaciousAubergine
4. ksun48
5. Endagorion
6. Benq
7. gisp_zjz
8. neal
9. Um_nik
10. yasugongshang

Information about prizes will appear soon.

Hello everybody!

Today, on March 1st, 2020 the final round of Technocup olympiad for Russian-speaking high school students is held. The round starts at 13:00 Moscow time.

For those who want to compete on the same problems, we will host two Codeforces rounds: one for the first, and one for the second division. The rounds will start at 13:05 UTC, don't miss them! The round will start just after the onsite contest ends, so it can be postponed slightly if the onsite event timetable changes.

If you compete in the Final Round today, you can't compete in the Codeforces round #625.

The problems are prepared by MikeMirzayanov, Endagorion, tourist, Roms, vovuh, voidmax, adamant and me. Many thanks to KAN, AndreySergunin, antontrygubO_o, kuviman, MrPaul_TUser, Stepavly, artsin666, Pavs, AdvancerMan, Stresshoover, Peinot, geranazavr555, defolaut, nuipojaluista, cannor147, PrianishnikovaRina and Pavlova for testing the problems!

P.S. Because of the onsite contest, some Codeforces features may be disabled today.

Good luck!

UPD: The editorial is here.

Congratulations to the winners of the round:

Div1

1) ksun48

2) maroonrk

3) jijiang

4) Radewoosh

5) Um_nik

Div2

1) DraqonLore

2) DishonoredRighteous

3) 99824485311011

4) endbringer

5) cml

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 and second Kotlin Heroes competitions which was held previously. Congratulations to the top 3 winners:

Episode 1

1. Petr
2. ecnerwala
3. eatmore

Episode 2

1. tourist
2. eatmore
3. Benq

Ready to challenge yourself to do better? The third "Kotlin Heroes" competition will be hosted on the Codeforces platform on Feb/27/2020 16:35 (Moscow time). 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.

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Hello! Codeforces Round 624 (Div. 3) will start at Feb/24/2020 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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Thanks to Artem Rox Plotkin and Dmitrii _overrated_ Umnov for help with testing the round!

UPD: It turned out that in the problem C, such a test exists that the answer overflows 32-bit integer type (int). Since such a test was not in the test set, many participants made such a mistake. We decided to forbid such tests, additionally guaranteeing that the answer fits in int.

UPD2: Editorial is published!