The 8th April Fools Day Contest will take place on Wednesday April 1st. This is a joke competition in which solving the problem is often easier than figuring out what the actual task is.

In this round you'll be given several weird problems and 2 hours to solve them. The contest will use ACM ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them), and it will be unrated. You can submit solutions in any language allowed by Codeforces, unless the problem says otherwise. To get an idea of what the contest will look like, you can check out the contests of the past years: 2012, 2013, 2014, 2016, 2017, 2018, 2019.

As usual, to enjoy competing in this round you'll need a sense of humor compatible with mine. Good luck, and have fun!

Hello Codeforces!

I am glad to invite you to my first official round Codeforces Round #630 (Div. 2), which will take place on Mar/31/2020 16:35 (Moscow time) (please note for the unusual starting time) and will be rated for all Division 2 participants.

You will be given 7 tasks and 150 minutes to solve them.

All tasks in this round were prepared by me. Hope that you will enjoy those tasks!

I would like to thank:

• pikmike for great coordination of this round, and the idea of solution of one task!

• Nanako, nezzar for useful discussion and testing this round!

• antontrygubO_o, McDic, vovuh, Flowerandyouth, socho, Oak_limy, Amori, Stresshoover, I1I1I11I1I1, defolaut, hx073269 and Pavlova for testing this round and invaluable suggestions!

• MikeMirzayanov for great systems Codeforces and Polygon!

To avoid queueforces, we will provide small amount but strong (hope so) pretests for first few tasks. Hope it works!

Score distribution will be announced later.

Good luck and have fun!

UPD1: Score distribution: 500-1000-1250-1250-1750-2250-3000

UPD2: Contest is over, and here is the editorial.

UPD3:

I am sorry that pretests were not as strong as I excepted.

Congratulations to the winners:

div1+div2:

1. vepifanov

2. xyz32768

3. PinkRabbit

4. 300iq

5. nuip

div 2:

1. xyz32768

2. sorry_to_tourist

3. camilla

4. jerome_wei

5. [user: _dawn]

people who were first to solve each task:

A: wangjunrui

B: MagentaCobra

C: okwedook

D: wangjunrui

E: GsjzTle

F: yooooooooo

G: GoGooLi

Lastly, thanks to Handsome2004 for the brilliant hack of E.

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Hello! Codeforces Round #629 (Div. 3) will start at Mar/26/2020 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 ZeroAmbition Stepanova, Mikhail pikmike Piklyaev, Maksim Ne0n25 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: Also thanks to Vitaliy kuviman Kudasov for testing the round!

UPD2: Editorial is published!

Hello Codeforces!

On Mar/23/2020 17:35 (Moscow time) Educational Codeforces Round 84 (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 Ne0n25 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, Codeforces.

I hope you wash your hands and feel great.

I added the support of 64-bit g++. If you are using Windows, you can easily install it via our minimalistic package manager PBOX running the command line pbox install msys2-mingw64-9.

Your solutions are compiled with the command line g++ -static -DONLINE_JUDGE -Wl,--stack=268435456 -O2 -std=c++17 program.cpp.

Now you can try to use int128 and other 64-bit specific features! In fact, I am slightly worried that the presence of such features may widen the gap between C ++ and other languages. Wait and see.

Currently, support for 64-bit C++ is experimental. For example, I would not be surprised if IO on it works slower in some cases (it is necessary to test!). I invite you to join the testing and experimentations. Share your impressions in the comments!

Hi!

On Mar/19/2020 17:35 (Moscow time) we will host Codeforces Global Round 7.

It is the first round of a 2020 series of Codeforces Global Rounds. The rounds are open for everybody, the rating will be updated for everybody.

The prizes for this round:

• 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 2020:

• 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.

The problems of this round were developed by isaf27 and me. Thanks to the testers mohammedehab2002, Taran_1407, Aleks5d, Endagorion, 74traktor, HIR180, dlwocks31,ToTheMoon, coyorkdow, Tzak, DomiKo, JustasLe, Hyado, Nemo, tattosha_aptan, Jatana, and (language corrector!) caoash.

Thanks to XTX, which in 2020 supported the global rounds initiative!

Good luck!

UPD: Score distribution: 500 1000 1000 (1000-1000) 2500 (2000-1500) 4000

UPD: Editorial!

Hi!

Codeforces round #628 (vintage Codeforces round #2) will take place on Mar/14/2020 17:35 (Moscow time). It's rated for the second division, but, as usual, first division participants can take part out of competition.

The problems were created by me. I'd like to thank, and orz, antontrygubO_o for coordinating the round; ramchandra, pajenegod, aryanc403, Taran_1407, Kuroni, mcdx9524, dorijanlendvaj, Andreasyan, 300iq, zoooma13, Osama_Alkhodairy, Mohammad_Yasser, and DeadPillow (special shout-out) for testing the round; and of course MikeMirzayanov for the great codeforces and polygon platforms.

You'll be given 6 problems and 2 hours to solve them.

UPD: the scoring distribution will be 500-750-1250-1750-2500-2750.

UPD: the editorial is out.

UPD: congratulations to the winners!

Div.1:-

1. tmwilliamlin168
2. MiFaFaOvO
3. Um_nik
4. imeimi
5. HIR180

Div.2:-

1. davooddkareshki
2. rainboy
3. PouyaNavid
4. _Lucien
5. socho

Good luck & Have fun!

UPD: Pay attention to the changed start time of the competition.

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Hello! Codeforces Round #627 (Div. 3) will start at Mar/12/2020 16:05 (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 ZeroAmbition Stepanova, Mikhail pikmike Piklyaev, Maksim Ne0n25 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!

UPD2: Editorial is published!