As-salamu alaykum, Codeforces! (Peace, Codeforces!)

We are glad to invite you to Codeforces Round 673 (Div. 1) and Codeforces Round 673 (Div. 2), which will take place at Sep/27/2020 18:05 (Moscow time) (notice later time than usual). The round is rated for both divisions. Each division will be given 6 problems to solve in 2 hours.

Problems were prepared by nkamzabek, bthero and me DimmyT.

We are very grateful and would like to sincerely thank the following people for their assistance in preparing the round:

• BledDest for the brilliant coordination of our round.

• adedalic, kdjonty31, Prakash11, namanbansal013, RockyB, Retired_cherry, saurabhyadavz, morzer, Mohamed.Sobhy, coderz189, hugopm, Tlatoani, dorijanlendvaj, and Roms for testing the problems and providing helpful feedback and suggestions.

• MikeMirzayanov for the amazing platforms Codeforces and Polygon.

This is our first round, we hope that the problems will be interesting and that the round will pass without issues.

Score distribution:

Div2: 500-1000-1500-2000-2500-3000

Div1: 500-1000-1250-2000-2250-2750

Wish everyone good luck and high rating!!!

UPD: problem ideas

UPD: Editorial Out

Congratulations to everyone, contest passed without issues!!!

Div1:

1. tourist

2. ksun48

3. maroonrk

4. 300iq

5. Aidos

Div2:

1. poorboy

2. kaisel

3. immortalhunt

4. hieu_2004

5. _dg_

Hello Codeforces Community. I would like to invite you all for ICPC Indonesia COMPFEST 12 Multi-Provincial Contest Online Mirror. I am the Person In Charge of the event.

I want to thank:

• Faculty of Computer Science, The University of Indonesia, for providing guidance and support for the official event.

• Our committee: hocky, JulianFernando, faustaadp, dewa251202, Defy_AK12, faishol27.

• Our testers: AMnu, stevenwjy, Yehezkiel

• MikeMirzayanov: for giving us the opportunity to host this online mirror. Also, for Codeforces and Polygon platform.

The online mirror will be held on , 3 hours after the official contest starts. Teams are allowed. The duration of the contest is 5 hours. For the official contestants, please refrain from joining this mirror contest.

Our problems are relatively easier than ICPC regional contests. However, we promise an interesting and diverse problem set. I'd say the overall difficulty is slightly more challenging than div two rounds. There might be an interactive problem. So make sure to familiarize yourself

About COMPFEST: COMPFEST is an annual event hosted by the University of Indonesia. It is the largest student-run IT event in Indonesia, and Competitive Programming Contest (CPC COMPFEST) is one of the competitions hosted.

Our contest on regional finder

Note: this contest is unrated.

UPD1: Editorial and contest review will be posted in a few hours, after we finish the official contest duty.

UPD2: Editorial is available here

Congratulations to the winners!

1. Extra Registration (LJC00118, xay5421, furry)

2. jiangly

3. Bajetii (theodor.moroianu, freak93, bicsi)

4. 未来ガジェット研究所 (wasa855, frame233, memset0c)

5. QAQAutoMaton

6. wlzhouzhuan

7. 2016wudi fan club (ChthollyNotaSeniorious, leukocyte, Cirno_9baka)

8. wucstdio

9. Sugar_fan

10. Teams Are For The Weak (IceKnight1093)

Hello, Codeforces!

I am very glad to invite you to the Codeforces Round #672 (Div. 2), which will take place in Sep/24/2020 17:35 (Moscow time). This round will be rated for the participants with rating lower than 2100.

All tasks were made by me, but gepardo helped me a lot with the last two tasks, probably these tasks wouldn't have appeared if he didn't help me.

My thanks to:

• antontrygubO_o for coordinating this round. With this great coordination only good tasks remained in the contest.

• gepardo made a lot, there wouldn't have been this contest if he didn't help me. He not only helped me with making last two tasks, but also helped me to understand how to make tasks for Codeforces rounds. Thanks!

• EIK this is the person who teached me competitive programming — my Informatics teacher. Thanks!

• programmer228, Hacktafly, K1ppy inspired me to make this round, listened for the every task idea, provided feedback and testing. Thanks!

• Osama_Alkhodairy, vamaddur, thenymphsofdelphi, Devil, Ari, SleepyShashwat, TechNite, Monogon, Tech.Maniac, Kavit_Kheni for testing the round and the tasks. Thanks!

• MikeMirzayanov for Codeforces and Polygon platforms. Thanks!

• You for participating in this round. Thanks!

You will have 2 hours for solving 5 tasks, one of which will be divided into easy and hard verions. I hope you will enjoy the round, I tried to make short statements and strong pretests interesting tasks.

Score distribution: 500 — 1000 — (1000 + 1250) — 2000 — 3000

UPD: The editorial is available. English version will be ready after the system testing is over.

UPD2: The english version of the editorial is ready.

Hello, Codeforces!

Artyom123, Kotehok3 and I are happy to invite you to Codeforces Round 671 (Div. 2), which will be held on Sep/19/2020 17:35 (Moscow time). This round will be rated for all participants, whose rating is lower than 2100 (We really hope so).

We would like to thank:

• isaf27 for coordinating the round and helping us <3
• dorijanlendvaj, physics0523, kdjonty31, FairyWinx, Retired_cherry, Osama_Alkhodairy, Mohamed.Sobhy, morzer, saurabhyadavz, thenymphsofdelphi, MagentaCobra, Prakash11, MarwanNabil, hugopm, I_love_teraqqq for testing the round and giving us useful feedback
• MikeMirzayanov for great Polygon and Codeforces platforms

You will be given 6 problems and 2 hours to solve them (or to play Valorant, because the contest is related to it for some reason). One problem has an easy version and a hard version.

You will have to help the agents from the game to grind that rating. Try your best as if you are playing ranked and they are your teammates!

gl hf

Here is the score distribution:

500 — 750 — 1250 — (750 + 1000) — 2250 — 3000

UPD: Editorial

Hello Codeforces!

On Sep/14/2020 17:35 (Moscow time) Educational Codeforces Round 95 (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 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:

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

UPD: Due to the issues with problems A and B the round is unrated.

UPD: Editorial is out

Hello Codeforces!

gyh20 and I are glad to invite you to Codeforces Round 670 (Div. 2) which will start on Sep/12/2020 16:45 (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 me and gyh20. This round is rated for participants whose rating is not higher than 2099. You can see that my current rating is exactly 2099 :)

There might be an interactive problem. You can learn about them here.

We would like to thank:

• isaf27 for coordinating and helping us with the problems.
• namanbansal013, Retired_cherry, morzer, Osama_Alkhodairy, TechNite, coderz189, physics0523, _zzw4257 for testing the problems and providing useful feedback. Special thanks to TechNite for helping us with writing the editorials, and physics0523 for improving one problem's solution!
• c2020HXW, Time_tears, fangzhijian2020 for discussing the problems with us.
• finally, MikeMirzayanov for great platforms Codeforces and Polygon!

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.

Good luck and have fun!

Upd: Score distribution is 500-750-1250-1750-2500.

Upd: For problem reasons, the contest is delayed for 10 minutes. We are very sorry to keep you waiting, sorry again.

Upd: Score distribution is changed to 500-1000-1500-2000-2750.

Upd: The round is finished. We're really sorry for B being well-known (none of the testers knew the harder version of this problem in ABC173E). Still, congratulations to the winners!

Div1 (unofficial):

1. WZYYN
2. Geothermal
3. kort0n
4. neal
5. kotatsugame

Div2:

1. JSoap
2. DemolitionLovers
3. killyou
4. gmh77
5. SkyStar

Upd: Editorial is out here.

Hello Codeforces!

My name is Vitaly Aksenov and I present you the new lesson in English EDU section as a part of "ITMO Academy: pilot course". I will talk about Disjoint Sets Union (DSU).

A little bit about myself, I cannot brag about being red (International Grandmaster), however, I was twice and each time afterwards there was a revolution of colours on Codeforces. :-) Right now I am the Researcher in ITMO University in parallel and distributed computing (link). Also, I am in Jury Committee of several olympiads such as NERC, Bioinformatics Contest, Russian Code Cup and etc.

This is my first time to write a lecture so do not judge harshly. I hope you will like it!

I want to thank pashka for video editing, and thanks to pashka, MikeMirzayanov and niyaznigmatul for sharing the problems.

More about EDU section you can read in this post.

MikeMirzayan and I are glad to invite you to Codeforces Round 669 (Div. 2), which will take place on Sep/08/2020 17:35 (Moscow time). The round will be rated for all the participants with rating strictly less than 2100.

The problems were created and prepared by MikeMirzayan and i.e. We would also like to thank everyone who was involved in the round preparation:

• antontrygubO_o for round coordination and high sense of taste that made our contest IDEAl.

• talant, Tlatoani, hugopm, Keshi, jouIej, jo_ulej, dick, Ari, AmShZ, rip, Devil, morzer, baby_baby_baby_ooh, Prakash11, Retired_cherry, Programmer, saurabhyadavz, _overrated_, LordVoldebug, LordVoIdebug, Kaurker for high-quality testing.

• MikeMirzayanov for Polygon and Codeforces platforms.

You will have 2 hours to solve 5 tasks. One of them is interactive, you should know how to deal with them.

Special thanks to my amazing minipig Schweine, who inspired us during the entire preparation time.

Scoring will be announced shortly before the round.

UPD1: There will be no pictures of minipig in the statements. :)

UPD2: The scoring is 500-1000-1500-2000-2500.

UPD3: EdItOrIaL.

UPD4: Congrats to winners!

Div1 + Div2:

1. ksun48

2. WZYYN

3. tribute_to_Ukraine_2022

4. neal

5. jiangly

Div2:

1. Hoxilo

2. deep_fake

3. GiannisAttemptafreethrow

4. watemus

5. wasureta

Hello Codeforces!

We are glad to invite you to Codeforces Round 668 (Div. 1) and Codeforces Round 668 (Div. 2), which will take place on Sep/06/2020 17:35 (Moscow time).

The problems were created by Ari, Kuroni, Merripium, Monogon, antontrygubO_o and hugopm.

We would like to thank:

• dorijanlendvaj, Jatana and enoone for helping with the preparation of the tasks.

• gamegame for always being nice and supportive.

• DatVu, Merripium, MofK and atoiz for stealing the round #666, forcing us to retheme around ponies.

• Monogon for making the author list more colorful.

• redblossom, thenymphsofdelphi, qlf9, mcfr, Tlatoani, aohkgnadnart_, McDic, cup_of_tea, bestial-42-centroids, Noam527, Mbfibat, wolfris, ffao, Falseeee, fpc_coder and fivefourthreeone for testing.

• MikeMirzayanov for the Codeforces and Polygon platforms.

There will be 5 problems in each division and will be given 2 hours to solve them (or post memes in the comments if you can't solve any).

We tried to make interesting problems, short statements, useful samples and strong pretests, and we hope you will like it.

Scoring will be announced shortly before the round and editorial will be posted shortly after the round (it is already written).

Good luck!

UPD: The number of problems is now 5 in each division.

UPD2: Score distribution:

• Div.1: 500 — 1000 — 1500 — 2250 — 3000
• Div.2 : 500 — 1000 — 1750 — 2250 — 3000

UPD3: Editorial is out

UPD4: We are sorry for problem div1E being well-known. No setter or tester have seen this problem. We apologize and hope you still enjoyed the contest.

UPD5: Congratulations to the winners:

Div.1

1. maroonrk
2. ainta
3. ko_osaga
4. Itst
5. hos.lyric

Div.2

1. minhchauxinhdep1234
2. potato167
3. guangmutianwang
4. w_o_kje
5. veckoper