On 02.03.14 there was a serious technical failure: Codeforces and related infrastructure hard drives have been corrupted. Unfortunately, it turned out that in contrast to all other components, the Codeforces database was not replicated properly. Polygon and Gym files were not injured. However, the Codeforces data has been significantly damaged.

We've rolled back the system to the state on February 7. It will remove 22 days of Codeforces life. Immediate efforts will be directed at the total exclusion of such situations. This is a very serious loss for me personally, which I can only blame myself.

Many thanks for all of you who supported us on a temporary Codeforces page. You helped much to find motivation in this difficult situation.

Currently the Gym is disabled. It will be opened back soon. We will return official contests and gym trainings with problems (but not results).

Data to be recovered:

• official contests with problems (but without results);
• public trainings in Gym;
• non-public trainings in Gym, but we do not know their owners — write me if you've prepared non-public training in Gym (not a mashup).

Sorry again for the inconvenience.

Hello everyone!

Codeforces Round #228 (Div. 1 and Div.2) will start at Monday, 3 February 2014, 19:30:00 MSK.

This is my 2nd round on Codeforces. (Click here to see my last round) , As usual, there will be 7 problems: 2 for Div2, 2 for Div1 and 3 for both. And same with the last round, the main character of all problem will be Fox Ciel.

I would like to thank Gerald for testing, and MikeMirzayanov for the Codeforces project including polygon system.

Good luck and have fun!

The score distribution will be published later. And the editorial will be published right after the system test.

By the way, yesterday is the Chinese new year. So I'd like to say Happy New Year to everyone who celebrate it! And I'm very glad to be the writer of the first round in the new year.

Update1: Good news for participants of Petrozavodsk training camp. Top 20 participants of the camp by this round results will get t-shirts from Codeforces.

Update 2: The score distribution for Both Division is regular (500-1000-1500-2000-2500).

Update 3: We postpone the round 10 minutes by technical reasons (dinner on Petrozavodsk Training Camp), sorry for the inconvenience.

Update 4: We've increased the contest time by 5 minutes.

Update 5: Contest ended, thanks for your participating! I'll post the editorial soon.

Update 6: Editorial.

Winners:

DIV1:

1. tourist
2. PavelKunyavskiy
3. Egor
4. 2222
5. dreamoon_love_AA

Sadly no one solved E correctly. Egor's solution can pass if the TL is 7 seconds instead of 6, what a pity!

DIV2:

1. I_love_Hoang_Yen
2. iaacboy
3. GoldExperience
4. shivatejesh
5. lordpawel

They are the only people who solved all tasks!

Hello!

Soon (on January 30 at 19:30 MSK) you are lucky to participate in Codeforces Round #227 for Div. 2 participants. Traditionally, Div. 1 participants can take part out of the competition.

Problems have been prepared by me. I want to thank Gerald Agapov (Gerald) for help in preparation of this round, Mary Belova (Delinur) for translation of statements, Michael Mirzayanov (MikeMirzayanov) for marvelous Codeforces and Polygon systems.

The main character of the tasks is the cat George.

UPD1: Scoring will be next: 500, 1000, 1500, 2000, 2500.

UPD2: Contest finished, congratulations to winners!

1. hmm_dream_big
2. graphis
3. InternationalGrandmaster
4. Skedar
5. mateusz

UPD: Editorial

UPD: Statistics

Hello!

Soon, on January 24th at 19:30 MSK, you are lucky to participate in Codeforces Round #226 for Div. 2 participants. Traditionally, Div. 1 participants can take part out of the competition.

Problems have been prepared by: Aleksey Chesnokov (CleRIC), Kirill Butin (KirillB) and Ivan Popovich (NVAL). This is the first round prepared by us and we hope that everything will be OK.

During the round you will be helping to the hero of the problems — usual bear.

We want to thank Gerald, Delinur, Aksenov239 and MikeMirzayanov for the system.

Scoring: 500-1000-1500-2000-2500.

Good Luck!

UPD: Round rescheduled for 5 minutes later

UPD: Editorial

UPD: We hope that you liked round.

Congratulations to winners:

1. cptbtptp

2. SquirrelDetected

3. MahooshojoNHB

4. Dong5k

5. yada

Hello everyone!

We invite you to participate at Codeforces Round #225, scheduled Monday, 20th January at 7:30 PM MSK. This is the third round I coauthor, along with Codeforces Round 198 (Div. 1) (and of course Div. 2 version of contest) and Codeforces Round 191 (Div. 2).

If you recall my old rounds, you'll see that main character is Iahub. The other writer of this round is... Iahub... the real person corresponding to "Iahub" character. Let me introduce you to Rares Buhai (rares.buhai). He's the author of Div. 2 C / Div. 1 A, Div. 1 D and Div. 1 E. You can expect those problems to be interesting, coming from a 2 times IOI gold medalist (being allowed to participate 2 more times). All other problems are created by me. I like them, but I wouldn't be objective if I said that they're interesting. Let's see if someone will think so after the contest :)

Like last time, I'll give you a little spoiler about the tasks. We tried to make the problem set as varied as possible. In order to get a good rank, one needs to be good at "ad hoc" problems as well as have good algorithmic knowledge.

As always, thanks to MikeMirzayanov for Codeforces platform, to Delinur for translating tasks, to Gerald for helping us prepare the round and to DamianS and ll931110 for testing it.

We wish everyone high rating and to have fun!

UPD Score distribution:

Division 1: 500 — 1500 — 1500 — 2000 — 2500

Division 2: 500 — 1000 — 1500 — 2500 — 2500

UPD Contest is over! Thanks for everyone who participated! I need to say we're impressed of your creative and totally unexpected solutions for Division 1 D.

Div. 1 winners:

1. yeputons
2. Arcueid
3. Dmitry_Egorov
4. ACMonster
5. scott_wu

Div. 2 winners:

1. Sick_coder
2. akaring
3. c0d3junki3
4. raihatneloy
5. sky0917

UPD Editorial

Good day everybody)

Welcome to regular Codeforces round #224 for Div.2 participants, first Div2 Only in new 2014 year:). As always Div.1 participants can take part out of the competition.

The problems were prepared by authors Pavel Kholkin (HolkinPV) and Gerald Agapov (Gerald). I can't already remember exactly in how many rounds I participate as author, co-author of just active assistant) Traditionally thanks to Michael Mirzayanov (MikeMirzayanov) for perfect Codeforces and Polygon systems and Mary Belova (Delinur) for translating the problems.

UPD: Score distribution will be dynamic, but the problems will be in supposed order of increasing complexity. The first dynamic round in this year)

We wish everyone good luck, high rating and excellent mood)

UPD2: the contest is over, we hope you enjoy it) the editorial is already here)

Congratulations to winners:

1) tankmagiciangirl
2) NagaiNatsuyasumi
3) lijian3256
4) TankKiller
5) dashabi

The contest Testing Round 9 is a special contest to test recent Codeforces internal improvements. Please, take part in it to help us to be ready for Codeforces Round 224 (Div. 2).

The Testing Round 9 will be completely unofficial and unrated. We will use problems from some Saratov contests, they will be new for many of you.

If you see any issues in Codeforces behaviour, write a comment here.

Thank you!

UPD. The contest completed. Thanks to all the participants.

Hello everyone!

Codeforces Round #223 will take place on Sunday, January 12th at 19:30 MSK. This is my tenth Codeforces round and I hope not the last.

I'd like to thank Gerald for helping me to prepare the round. Special thanks to Delinur for translation of all problem statements into English.

I strongly recommend you to read ALL the problems.

This is the first round this year. Incidentally, the first round last year for both divisions was also mine (by statistics +1/-1 is was the coolest of rounds that I gave). I hope that this time the problems will be even more interesting for you. Will it? Will find it out after the round :)

Gl & hf ! :)

Problem point values will be standart for both divisions.

Hurry! Only until the 10th of January, you can change your handle! Note that it will be possible to roll back the changes or change the handle again only after a year.

Talking about handles I always reminisce the following story. Once a user wrote me the message: "Please change my handle from I_love_Valya to I_love_Sveta, as I no longer love Valya ..."

Happy New Year!

Hello! Do you feel the breath of New Year?

The clock shows a day before New Year, so it is time to sum up the past. I do not have speech-writers for words in the style of "what recently seemed almost impossible, it becomes a fact of life" so I'll be short. Thank you all! Your unfading interest and constant help inspire Codeforces team for new achievements! Brilliant writers, invisible soldiers: testers, tireless and greedy for knowledge participants — all of you help Codeforces do better!

I've dug into the records and made a partial list of the most notable major improvements of 2013. Some large improvements of our infrastructure are not in the list, as the community can not see them directly.

• A simple way to add contest from Polygon to Codeforces::Gym.
• Drafts embedded in text form fields in Codeforces and Polygon.
• Multiple interface improvements in the contest area.
• Many improvements of Testlib.
• Notably improved performance of Polygon on large manual tests.
• Repeatedly updated compiler versions to the nearly latest.
• Supported languages: MS C#, Python 3, Go, JavaScript V8.
• Updated Codeforces testing servers.
• Polygon supported HTTPS.
• Organized the first season of weekly Codeforces trainings 12 episodes.
• Supported organizations in the profile and rating of organizations.
• Added numerous contests to Codeforces::Gym. Probably the most valuable — a large number of Andrew Stankevich Сontests.
• Implemented checker and validator tests in Polygon.
• Implemented macro language support in test scripts in Polygon.
• Groups on Codeforces have appeared, they can contain contests and blogs.
• Introduced Mashup Contests — special contests for personal and group training, can be easily composed by problems from rounds or from Polygon.

In addition, in 2013 we not only hosted 64 classical Codeforces rounds, but hosted some tournaments:

• Croc Champ 2013
• MemSQL start[c]up
• ABBYY Cup 3.0

Also we took a role of ACM-ICPC 2013 World Finals Press Partner!

And as the detective story can not be without a chase, and the annual report can be do without the fun pictures. Here is a series of images showing the growth of Codeforces: