Hi!

On Jul/25/2021 17:35 (Moscow time) we will host Codeforces Global Round 15.

This is the third round of the 2021 series of Codeforces Global Rounds. The rounds are open and rated for everybody.

The prizes for this round are as follows:

• 30 best participants get a t-shirt.
• 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive.

The prizes for the 6-round series in 2021:

• In each round top-100 participants get points according to the table.
• The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest.
• The best 20 participants over all series get sweatshirts and place certificates.

Thanks to XTX, which in 2021 supported the global rounds initiative!

Problems for this round are set by cip999 and me. Thanks a lot to the coordinator antontrygubO_o, to the testers gamegame, ajit, golions, skydogli, McDic, rabaiBomkarBittalBang, nweeks, Marckess, HenriqueBrito, gratus907, bWayne, zscoder, TheOneYouWant, and to MikeMirzayanov for the Codeforces and Polygon platforms.

You will be given 9 problems and 2 hours 45 minutes to solve them.

The scoring distribution is 250-500-1000-1000-1500-1500-2500-2750-3750.

Good luck and see you in the standings!

UPDATE 1: Thank you very much for participating, we hope you liked the problems (and sorry to top contestants for giving a not-so-fresh problem I).

Here you can find the editorial (with a bit of behind-the-scenes, some obscenely wrong preditions, and hints for all the problems).

UPDATE 2: Congratulations to the winners!

1. tourist
2. ksun48
3. Benq
4. Petr
5. peehs_moorhsum
6. TadijaSebez
7. sunset
8. Um_nik
9. ko_osaga
10. dreamoon_love_AA

Hello, Codeforces!

I'm glad to invite you to amazing (we've tried to make it such) Codeforces Round #734 (Div. 3) which will start on Jul/23/2021 17:35 (Moscow time). This round is the first "trial of the pen" of me (MrPaul_TUser) and it seems to be hard to make it alone — a significant contribution was made by MikeMirzayanov, BledDest and DK318.

The round contains 6-7 problems. The difficulties of the problems are expected 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 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 6-7 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 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 WolfBlue, BlueDiamond, harlequen, -is-this-fft-, le.mur, Bench0310, Reiva5, Golovanov399 and Sho for testing the round and improving tasks.

Good luck and have fun!

UPD

Editorial

Hey, Codeforces!

We have great news for you.

Harbour.Space University is excited to announce a new contest for all interested programmers who want to start their studies in Barcelona, Spain or Bangkok, Thailand, and join our ICPC team.

The contest will be hosted on the Codeforces platform Jul/22/2021 17:35 (Moscow time). We have prepared 9 problems of the joined (Div1 + Div2) level. The round will be rated and open for everyone.

UPD: Scoring distribution: 250-500-750-1250-1750-2500-3000-3750-5250

UPD2: The editorial is out!

For the next academic year (2021/22), we are recruiting a fascinating community of competitive programmers from the top prize-winners of international Olympiads to join one of our competitive programming teams at the university.

In the next few years, our goal is to win SWERC and compete at a high level in the ICPC globally. Therefore we want to invest a serious amount of our energy, resources, and talent into these activities.

That’s why we are inviting you on an exciting journey in the company of like-minded people, outstanding coaches, and our ongoing partnership with Codeforces.

We have already organized over 100 educational rounds, so we think the time has come to test our joint efforts and reward the most diligent.

Here’s what you win if you place in the contest:

,

The monthly living allowance throughout the entire duration of studies depends on the overall performance of the candidate. As a guidance, it is in the range of 500-1500 EUR (it might be applied to the contestants who win 4th-10th places).

*No application fee is required for any of the awards listed above.

We would like to say a word of appreciation to:

• Round Coordinator: BledDest
• Authors: kefaa2, bthero, Adel_SaadEddin, Zaher, Errichto, marX.
• Testers: nooinenoojno, Batrr, Utkarsh.25dec, Um_nik, adedalic, Wind_Eagle, abunyawa, aniervs, hitonanode, Aidos, thenymphsofdelphi, 221, ZetaZomB, RUMAZIUS, madxmad, Whirligig, Vladik.
• MikeMirzayanov for Polygon, Codeforces, partnership with Harbour.Space and making this round happen :)

Editorial is out

Good luck, and may the code be with you!

Harbour.Space University

Hello, Codeforces!

Welcome to the Codeforces Round #733 (Div. 1 + Div. 2, based on VK Cup 2021 - Elimination (Engine)) that will start on Jul/17/2021 17:35 (Moscow time). It will be a combined rated round for both divisions.

This round is a mirror of VK Cup 2021 Elimination. VK Cup is an annual championship for Russian-speaking competitors organized by VK — a social networking service based in Saint Petersburg and the most popular website in Russia. VK Cup started in 2012 and has grown to be a four-track competition in competitive programming, ML, design, and mobile development.

All the problems were authored and prepared by me. Big thanks to everyone without whom this round would not be possible: PavelKunyavskiy, KAN, lperovskaya, ksun48, Sert, Aleks5d, MikeMirzayanov.

You will be given 8 problems and 3 hours to solve them. It is recommended to read all the problems. Good luck!

UPD: Scoring distribution: 500 — 750 — 1000 — 1500 — 2000 — 2750 — 3750 — 4750

UPD2: Congratulations to the winners!

VK Cup 2021 — Elimination (Engine):

1. Um_nik
2. Petr
3. Endagorion
4. Golovanov399
5. kefaa2

Codeforces Round #733:

1. jiangly
2. ecnerwala
3. Radewoosh
4. maroonrk
5. Benq

Editorial of problems A-E is out, problems F-H will appear later.

UPD3: Editorial now contains problems F-H as well.

Hello Codeforces!

On Jul/14/2021 17:35 (Moscow time) Educational Codeforces Round 111 (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:

Hey, Codeforces!

From Barcelona to Bangkok, we are officially opening our new campus in August.

As some of you might know, Harbour.Space University has partnered with the University of the Thai Chamber of Commerce, Bangkok to offer exceptional tech specialists the opportunity to study in one of the most dynamic and vibrant cities in the world.

To celebrate our launch, we have scholarships available for our tech bachelor’s and master’s programmes including Data Science, Cyber Security, Front-end Development and Computer Science.

Scholarship Requirements:

• Proficient level of English
• CV
• Maths and Computer Science Test
• Diploma and transcript of the highest attained education level

For the Front-end Development Master’s programme, applicants will have to submit a challenge.

We are always happy to see Codeforces members join the Harbour.Space family. Get a chance to learn from the best in the field and kickstart your career and apply now to one of the following programmes:

• Data Science
• Cyber Security
• Front-end Development
• Computer Science

Keep in touch and follow us on LinkedIn for more scholarship opportunities. And follow us on Instagram to evidence student life, events, and success stories from our apprenticeship program students.

Good luck on your round, and see you next time!

Harbour.Space University

Congratulations to the winners:

289 successful hacks and 677 unsuccessful hacks were made in total!

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

UPD: Editorial is out

Hello, Codeforces!

I'm glad to invite you to Codeforces Round #732 (Div. 1) and Codeforces Round #732 (Div. 2), which will be held on Jul/11/2021 17:05 (Moscow time). Note the unusual start time of the round.

The round will be rated for both divisions. Each division will have 6 problems and 2.5 hours to solve them. There may or may not be an interactive problem, so I suggest you should read the guide for interactive problems.

All problems were written and prepared by CoupDeGrace, kuangbin, mejiamejia, Heltion, Melacau, Nanako, GOATWU, Cirno_9baka, Suiseiseki, ODT, box, Ynoi, syh0313, wh0816 and me.

And thanks to QAQAutoMaton, gamegame, starusc, interestingLSY, chenkuowen, DataStructures, 1-gon, ijxjdjd, Schwarzenegger, sunsiyu, Nezzar, senyaa, TheOneYouWant, gyz_gyz, kimoyami, njupt_lyy, 221, growup974, Manik, absi2011, gyh20, errorgorn, antontrygubO_o, oolimry, zhangzx123, m371, Proszek_na_ludka, SonDinh, triple__a, Pecco, AzusaCat, dorijanlendvaj, Imakf, Forever_Pursuit, JAMMY for testing and good advice, isaf27 for his excellent round coordination and help with preparation and MikeMirzayanov for great systems Codeforces and Polygon.And you, for participating!

This is my first round ever. Great efforts have been put in during the past six months. We are sincerely looking forward to your participation. We hope everyone will enjoy it.

Good luck!

UPD1: Here's the score distribution:

Div 1: 500 — 1000 — 1500 — 2250 — (2000+2000) — 4000

Div 2: 500 — 1000 — 1250 — 1750 — 2250 — 3000

UPD2: Sorry to everyone! This is my first round and I spent lots of time to prepare it. I prepared at least 23 problems, and chose these eight ones for this round. I invited 35 testers to test, and chose problems according to their feedback. However, the difficulty is more than expect.And the pretest is not strong, leading to FST for many people. I blamed myself sadly. So I must say sorry to you, my dear friends. I will improve myself in the future. Wish you good luck and happy everyday. (๑•ᴗ•๑)

UPD3: Tutorial is available.

UPD4: Congratulations to the winners

Div1:

1.gisp_zjz

2.peehs_moorhsum

3.xtqqwq

4.Swistakk

5.Endagorion

Div2:

1.ki_msaga

2.jkjung

3.RBurgundy

4.motomuman

5.flashsonic

Hello, Codeforces!

We, DK318 and unreal.eugene, are students of ITMO University. And we have recently joined the developers team of Codeforces and Polygon. We have prepared this round for more careful acquaintance with Polygon. Very soon you will be able to see the first results of our work as developers.

Except us, in round development participated MikeMirzayanov, geranazavr555 and doreshnikov. We hope that you will enjoy the competition!

Codeforces Round #731 (Div. 3) will start at Jul/10/2021 17:35 (Moscow time). You will be offered 7 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 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 7 problems and 2 hours 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 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 I_Remember_Olya_ashmelev, 1-gon, CtrlAlt, Tzak, FelixArg, antontrygubO_o, bugdone and brian for testing the round and improving tasks.

Good luck!

UPD 1

Editorial.

Hello Codeforces!

I and DK318, as students of ITMO University, joined the Codeforces team in June. Last month we mainly dealt with the development of the Polygon platform and were focused on one significant feature lots of people dreamed of.

Have you ever made some changes to the problem, and at the same time another person changed the same file? I believe most of you did and disliked this situation. If you wanted to resolve the conflict, you needed to download an archive containing all your changes and repeat them all in the newest revision of the problem. This was very confusing and time-consuming, wasn't it? And now we present probably the most anticipated feature of Polygon since its creation: a web interface for resolving conflicts.

Hello Codeforces!

I am quite excited to invite you to my first ever round, Codeforces Round #730 (Div. 2) which will start on Jul/07/2021 17:35 (Moscow time). The round will be rated for participants of Division 2 (having rating strictly less than 2100). As always, Division 1 participants are welcome to participate in the round but it will be unrated for them.

The problems of this round will be themed on the 2005 video game Need For Speed: Most Wanted. You will be given 5 problems and 2 hours 15 minutes to solve them. One of the problems will be interactive. So, it is recommended to read the guide on interactive problems before the round.

I would like to thank -

• Aleks5d for coordinating the round and not rejecting any of my problems :)
• KAN for reviewing all the problems and providing invaluable suggestions throughout the round preparation.
• mshiladityam and yash_daga for listening to my problem ideas even before I proposed them, providing invaluable suggestions and testing the round.
• Akulyat, andr0901, Mazaalai, talibmohd, nnv-nick, mcdx9524, DimmyT, kassutta, 4qqqq, m371, Karavaiev and asrinivasan007 for testing the round.
• amgfrthsp for translating the statements.
• MikeMirzayanov for the amazing Codeforces and Polygon platform.
• All the participants for participating.

I tried my best to create interesting problems with clear statements, strong pretests and useful sample test cases. Make sure to read all of them. Good Luck and Have Fun. See you on the Blacklist ranklist.

The score distribution is here: $$$500-750-1500-(1000+1250)-3000$$$.

UPD: Editorial

UPD: Congratulations to the winners

Div. 1 + Div. 2 -

1. Geothermal
2. Golovanov399
3. SSRS_
4. uwi
5. tfg

Div. 2 -

1. h0up1ngze
2. rsabcmoi
3. TabulaRasa7
4. LordVoIdebug
5. islingr

First Solves -

A: Geothermal
B: Geothermal
C: rsabcmoi
D1: h0up1ngze
D2: Golovanov399
E: tfg

Hello Codeforces!

tianbu and I are glad to invite you to Codeforces Round #729 (Div. 2) which will start on Jul/03/2021 16:05 (Moscow time). Note the unusual start time of the round.

The contest will last for two hours, and you will have five tasks to solve. The tasks are prepared by tianbu and me. This round is rated for participants whose rating is not higher than 2099.

We would like to thank:

• Aleks5d for coordinating and helping us with the problems.

• dorijanlendvaj, waaitg, Imakf, alexX512, Akulyat, talibmohd, LostCoder16, andr0901, nnv-nick, Delmos, kassutta, m371, 4qqqq, for testing the problems and providing useful feedback.

• amgfrthsp for translating the statement

• finally, MikeMirzayanov for great platforms Codeforces and Polygon!

It's the second time we hold our contest, our previous round Codeforces Round #670 (Div. 2).

We tried our best to make the statements short and clear, pretests strong and problems interesting. We hope you like the problems!

Score distribution will be announced shortly before the round.

Score distribution: 500-1250-1500-2000-(2000+1000)

Editorial is published Editorial

Congratulation to the winners:

Div1+Div2:

1.MiyoHijiriido

2.kefaa2

3.jiangly

4.Benaive

5.Ormlis

Div2:

1.MiyoHijiriido

2.Benaive

3.hehezhouyyds

4.TuNormie04

5.SoilCrystal