Hi!

On Jul/20/2019 18:35 (Moscow time) we will host Codeforces Global Round 4.

It is the fourth round of a new series of Codeforces Global Rounds supported by XTX Markets. The rounds are open for everybody, the rating will be updated for everybody.

You will be given 8 problems and 150 minutes to solve them. The scoring distribution will be 500-750-1250-1750-2000-(1500+1500)+3250+4000.

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 2019:

• 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 the whole series get sweatshirts and place certificates.

The problems of this round were developed by me. I will be available on Discord to discuss the problems after the contest.

I would like to thank:

• arsijo for his help in the round's coordination,
• 300iq, Aleks5d, arsijo, Ashishgup, Jeel_Vaishnav, khairy, _kun_, ksun48, Learner99, Noam527, StasyaCat, TonySnark, Um_nik for testing the round,
• MikeMirzayanov for Codeforces and Polygon,
• Pretest for being so strong, TLE for being so rare, system_test for being so fast and Editorial for being ready right after the contest finishes.

UPD: The round is finished. I hope you enjoyed the problems! I am very sorry about the issue on E.

UPD2: Editorial

UPD3: Congratulations to:

1. ainta
2. Radewoosh
3. tzuyu_chou
4. LHiC
5. Benq

Hi everyone! I'm glad to invite all of you to participate in Codeforces Round #574 (Div. 2) which will take a place in Jul/17/2019 17:35 (Moscow time).

This round is based on SIS team contest. You will be given 6 problems and 2 hours to solve them. This round will be rated for Div. 2 participants. In other words, this round will be rated for the participants with rating lower than 2100. As usual, participants from the first division are welcome to join out of competition.

Problems was invented and prepared by Nebuchadnezzar, Kurpilyansky, meshanya, TsarN, sava-cska, ima_ima_go and senek_k. I am just a coordinator of this round, I made a small amount of work such as English translations and editorials. I want to thank Mikhail MikeMirzayanov Mirzayanov for amazing systems Codeforces and Polygon, all authors of this great contest, KAN and _kun_ for help with difficulties estimating and choosing the problems and my dear friend Ivan BledDest Androsov for help with round preparation!

Good luck everyone and see only green system testing messages! :)

UPD: The scoring is 500 — 1000 — 1500 — (1000+1500) — 3000 — 3500.

UPD2: I would like to thank testers galloska, NatInTheHat and AlexPop28 for help and advices about the round!

UPD3: Editorial is published!

Hello Codeforces!

On Jul/14/2019 17:45 (Moscow time) Educational Codeforces Round 68 (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 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

What do you do on Friday evening? Are you busy? Will you take part in our round?

Hello, Codeforces!

We are glad to invite you to take part in Codeforces Round #573 (Div. 1) and Codeforces Round #573 (Div. 2), which will be held on 12.07.2019 17:35 (Московское время).

The round will be rated for all participants from both divisions.Participants in each division will be offered 6 problems and 2 hours (to be determined) to solve them. Both divisions will share 4 problems.

The problems were written and prepared by 2014CAIS01, tender, teitoku, winterzz1, chenjb, Subconscious, Claris, quailty, skywalkert and me.

Thank to:

• tender for providing stories for some problems.

• skywalkert, Claris, quailty, WhaleVomit, NIWIS, Intrincantation and isaf27 for testing this round and giving good advice.

• skywalkert for helping me to prepare and translate the statement and tutorial (and sorry for my poor English (╥﹏╥) ).

• scanhex for helping us to translate the statement to Russian.

• 300iq, KAN and MikeMirzayanov for excellent coordination of this round!

• MikeMirzayanov and his Codeforces team for amazing systems Codeforces and Polygon! (I like Codeforces forever! )

If you are not busy, please take part in our round on Friday evening! We wish you good luck and high rating!

The score distribution will soon be published.

UPD1: Some of authors will be at the Discord CP Community to discuss the problems after the coding phase. However, please follow the rules and don't discuss the problems before or during the contest by any means.

UPD2: List of contributors is a bit changed, and the scoring distribution will be:

• Div.2: 500 — 1000 — 1500 — 2000 — 2500 — 2500

• Div.1: 500 — 1000 — 1500 — 1500 — 2250 — 2750

UPD3: Sorry for forcing you to spell our nicknames, 'tokitsukaze' and 'quailty', and some ambiguity in the statements. Anyway, we sincerely appreciate your participation.

UPD4: Editorial

UPD5: Congratulations to the winners!

Div.1:

1. Um_nik

2. Benq

3. ATS

4. tmwilliamlin168

5. Rifai

Div.2:

1. RannRu

2. cyy233cnbb

3. anand.oza

4. puppies_and_rainbows

5. calabash_fool

UPDATE: the editorial is here

Link to the online mirror

Hello CodeForces! This year again, I'd like to invite you to the online mirror of an open championship of Switzerland called HC2 (the Helvetic Coding Contest). A mirror was also held one, two and three years ago.

The Helvetic Coding Contest is a yearly contest held at the EPFL in Lausanne by the PolyProg association. The contest itself took place on April the 13th, but the online mirror is scheduled on Sunday, 7th of July, 10:05 Moscow time. The duration is 4:30.

Rules:

• you can participate in teams or individually (1-3 people),

• standard ACM-ICPC rules (no hacking),

• the contest is not rated,

• if you have participated in the onsite contest, please do not participate in the mirror.

The contest this year is Doctor Who-themed. It features 5 series of 2-3 related tasks with increasing difficulty (easy/medium/hard). (For the online mirror, we will skip one series that had appeared in the onsite contest.) Sometimes it may be the case that a solution for the hard version solves all of them, but usually not. We think that the problemset is diverse and interesting, and while the contest is ACM-style, you will find that some problems are not so standard. Most easy&medium problems are even solvable in Python, so you can also recommend this contest to your newbie friends :) We promise to post a nice editorial as soon as the contest ends.

Acknowledgments: the problems were set by bgamlath, DamianS, esrever, milenkoviclazar, Wajeb (who coordinated), and myself. Thanks also go out to people who helped with the statements and testing: anayMehrotra, Michalina Pacholska (who also draws the cows), _kun_ for the Russian statements, KAN for CodeForces coordination, as well as everyone involved in the actual onsite contest, who are too many to name here. We also thank the sponsors Open Systems and nexthink. Lastly, thanks to MikeMirzayanov for CodeForces and Polygon (which was used to prepare the problems).

Finally, in a bit of autopromotion, note that you can use Hightail to automatically test your solutions :) Good luck!

After-contest UPDATE:

>>> Editorial <<<

Also:

• two extra problems from the onsite contest that were left out for the online mirror are available in the Gym

• the new uphacking feature is available for all problems except A3 and C3

Thanks to everyone who participated! We hope you have enjoyed the problems. The top three teams are:

1. 大象大象你的鼻子为什么那么长 (solved all 14 problems!): FizzyDavid, 300iq, TLE

2. zxtxdy (13 problems): cuizhuyefei, MarkF, zx2003

3. helveticow (12 problems): scott_wu, ksun48, ecnerwala

See you again next year!

Hi Codeforces.

Recently there have been several improvements on the website. A little later, I will write a short note about them. Here I want to tell about a noticeable new functionality that has recently been implemented by kuviman.

Sometimes after the end of a round there are requests in comments to add a particular test. And problem writers or coordinators add it manually. Now this process is automated.

Meet the uphacking phase!

Now, after the end of almost any contest, participants from Div.1 have the opportunity to hack any solution in this contest during the week. Yes, including official solutions from rounds. In case of successful hacking:

• Your test will be automatically added to the problem and will be used in the future when testing new solutions for this problem;
• If a hacked solution is a practice (i.e. upsolving), then its verdict will change to “hacked” otherwise its verdict will remain unchanged;
• The participant whose solution has been hacked will be notified via system private message;
• Each solution can be successfully hacked only once.

In order to add only adequate and reasonable tests, it is forbidden to hack solutions that intentionally contain a mistake. Please strictly follow this rule. It is because of the possibility of inadequate behavior that we cannot open uphacking for everyone.

I hope that this innovation will be useful and tests for problems will become even better!

• MikeMirzayanov

UPD: Probably, later we will extend uphacking phase and reduce the rating bound.

Hello, Codeforces!

We are glad to invite you to the Codeforces Round #572, which will be held on Friday, 5 July at 18:05. The round will be rated for both divisions (as this time we thanked MikeMirzayanov).

Round was prepared by us, antontrygubO_o and kefaa2. This is our first round, and, as we hope, not the last one!

A lot of thanks to arsijo for the excellent coordination of the round, gepardo, GandalfTheGrey, progmatic2, zoomswk, ecnerwala, AllCatsAreBeautiful, DmitryGrigorev, Markellonchik, dasfex, Taran_1407, slicedclementines, DenisPushkin, austrian_artist, mmello, sas4eka for the testing and valuable comments, and to Mike MikeMirzayanov Mirzayanov for the amazing platforms Codeforces и Polygon. (please rated)

Participants in each division will be offered 6 problems and 2 hours to solve them. We strongly recommend reading statements of all problems! The scoring distribution will hopefully be announced before the round begins.

We wish you good luck and high rating!

UPD1: Shortly after the contest, we'll be on the community Discord server to discuss the tasks.

UPD2: Slight corrections: participants in Div $$$1$$$ will be offered $$$5$$$ problems, one of which will have $$$2$$$ subtasks, while participants in Div $$$2$$$ will be offered $$$6$$$ problems, one of which will have $$$2$$$ subtasks. Please note that subtasks will be unusual this time and will differ not only by constraints.

UPD3:

Scoring distribution of Div $$$2$$$ round: 500 — 1000 — 1250 — (500 + 1250) — 2250 — 2750

Scoring distribution of Div $$$1$$$ round: (250 + 750) — 1250 — 1750 — 2250 — 2500

UPD4: Editorial

UPD5 Congrats to winners!

Div 1:

1. Um_nik

2. ugly2333

3. Radewoosh

4. Marcin_smu

5. Endagorion

Div 2:

1. esbee

2. handsomeIvan

3. philologist

4. teamskiy

5. NeoGul

Hello Codeforces!

On Jun/30/2019 17:45 (Moscow time) Educational Codeforces Round 67 (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 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,

Do you remember my post New: Diagnostics of Solutions in C++? If not, please read it.

Recently, I've implemented better UI to show you diagnostics. Now in on the status pages sometimes you can notice something like this:

Click to the and you'll see the code with the highlighted problematic line and description with the possible reason of the mistake.

Do you like it?

Hi everyone!

The rated Codeforces Round #571 (Div. 2) will take place on Jun/28/2019 11:20 (Moscow time). This round is based on the Kremenchuk Summer Programming Cup 2019.

The contest is prepared by Dalgerok, Karasick, StasyaCat, antontrygubO_o, danya.smelskiy, and me.

You will have 2 hours and 15 minutes to solve 6 problems.

Good luck!

We apologize for the issue that happened with the problem B. The round is unrated. If you want to read my emotional reply about it, please read this.