By K0T20 hours ago, translation, In English,

Hi everyone!

Codeforces Round #267 will take place on September 18th at 19:30 MSK My name is Yura and this is my first Codefocres round and I hope not the last.

I'd like to thank Fedor Korobeinikov (fk2012) and Alex Vistyazh (netman) for helping me to test all the tasks and prepare this round. Also, special thanks Gerald for helping me to prepare the tasks, Delinur for translation of all problem statements into English and MikeMirzayanov for Codefocres and Polygon.

I hope that everyone will find the problem for himself, and plunge into the student's life.

Good luck! =)

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By Nickolas3 days ago, translation, In English,

470A - Crystal Ball Sequence

As usual, the first problem tests competitors' ability to do basic math, and in this case it is even easier than the sample — without any loops.

$ 1+*3*1+.

470B - Hexakosioihexekontahexaphobia

This problem uses more advanced language concepts — loop, conditional execution and even named variables! Variables are convenient to use as loop counters and result accumulators, so as to avoid stack manipulations for the same purpose.

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By Nickolas4 days ago, translation, In English,

The contest is over. 13 people solved all problems — you guys are amazing!

The editorial will be available here.

Today's language is FALSE, stack-based esoteric programming language invented over 20 years ago.

The traditional A+B problem (integers A and B are separated with a space) can be solved like this.

To test your solutions, you can:

  • download source code in C of the original interpreter here. Testing system uses this interpreter with -q option.
  • use "Custom Invocation".
  • use online interpreters (they differ from the reference interpreter a bit but make debugging much easier): 1, 2.

Useful links:


  1. Language description contains instructions ø and ß. The reference interpreter uses O and B instead (both online interpreters support ø and ß).
  2. End of file is encoded as #-1, end of line — as #13#10.
  3. The stack MUST be empty when program completes, otherwise the interpreter will post an error to stdout, and output will be judged as incorrect.

Surprise Language Round #7 will take place on September 13th, the Programmers' Day.

The rules of the contest are as follows:

  • The contest is unrated for everybody.
  • The round uses ACM ICPC rules: the standing is defined by the number of solved problems, ties are resolved based on penalty time. Initially the penalty is 0, and for each solved problem it is increased by submission time (since the start of the contest) + 20 minutes for each failed submission. The solution is considered to be correct if it passes all tests from a predefined test set; you know whether the solution is right immediately after sending it. There are no hacks.
  • The round has 8 problems, sorted by estimated complexity, and you have 2 hours to solve it.
  • Solutions are accepted only in one language, which will be announced at the beginning of the contest. The language was created a while ago, we didn't invent it for this occasion.
  • Please reread this post at the beginning of the contest: we will announce the language and add instructions to install the compiler (the contest interface will provide an option to run your solutions online as well) and links to useful manuals. Other than that, learning the language is up to the competitor. You can use any resources to solve the problems (as long as you remember that this is an individual competition); you don't have to limit yourself to the manuals provided in the post.

I hope that the language I chose will be unknown to most of the competitors.

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By KaiZeR5 days ago, translation, In English,

Hi Codeforces!

We would like to invite you to participate in Codeforces Round #266 Div2, which will be held this Friday, September 12th at 19:30 MSK. As usual, Div1 participants can take part out of the competition.

Problems have been prepared by Antoniuk and me. It's the second round prepared by us, and we still hope it won't be the last.

We want to thank Gerald for helping to prepare this round, Delinur for translating the statements, and also MikeMirzayanov for Codeforces and Polygon.

It will be used a standart scoring: 500-1000-1500-2000-2500.

Gl & hf!

UPD. Round has finished. Thanks for participating.
UPD2 Congratulations to top-5 participants:

1) dominator_hza
2) Final_Battle
3) free_pascal
4) vanhanh.pham
5) fzmh

UPD3. Editorial .

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By MikeMirzayanov5 days ago, translation, In English,

Welcome to 2014-2015 CT S02E01: Codeforces Trainings Season 2 Episode 1. The training duration is 4.30 hours. It is opened for teams as well as for individual participants. After the end you may use the practice mode to complete problem solving. Also it will be availible as a virtual contest for whose of you who can't take part today. Please, do not cheat. Only fair play!

It is possible that the problems will be too easy for some participants, it is possible that we will add some problems.

Good luck!

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By MikeMirzayanov6 days ago, translation, In English,

The new season of a collegiate team championship ACM-ICPC is about to start. For example, the registration for the Southern (Saratov) Subregional Contest is already running. I am sure that many participants of the Codeforces rounds will take part in ACM-ICPC this year.

We are launching a series of weekly practice trainings on Codeforces. Naturally, they will be held within Codeforces::Gym. Feel free to participate!

The practice starts on Thursdays at about 12:10 PM (UTC), which is 16:10 Moscow Time. Expected duration is 4-5 hours. We are going to practice using the problems of different contests of the past years. All you need is common sense and observing these simple rules:

  • We will not publish the problem source before the practice starts. We want you to solve the problems on your own in a fair competition. If you use somebody else’s code or cheat in any other way, you will be disqualified. If you don’t want to solve on your own, that’s fine, you don’t have to. But spoiling the practice for others is unacceptable.
  • Do not discuss the problems till the practice ends.
  • We will rarely answer the questions about problems. If you’ve found some obvious bug, please let me know. We will fix the bug and send everybody the note about the fix.
  • If you have a coach account (and you do not participate in the practice), we will be grateful for your help.
  • Please register for the practice with the people from your team who actually participates in it.
  • From time to time, I am going to ask some of the jury of the past contests or coaches from other higher educational institutions to help with preparing or share materials — your understanding and help will be greatly appreciated!
  • if you solved the contest problems before just switch to another training or inform us via problem questions form, we will move you to out-of-competition role.

The first contest 2014-2015 CT S02E01: Codeforces Trainings Season 2 Episode 1 takes place on September, 11, at about 12:10 PM (UTC).

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By Endagorion2 weeks ago, translation, In English,

Hi all.

On Sunday, September 7, at 19:30 MSK regular, 265-th, Codeforces round will take place. Problems are prepared by me, Mikhail Tikhomirov. Round will be for both divisions.

Standard (not dynamic) scoring will be used for this round.

Div. 1: 500-1500-1500-2000-2500

Div. 2: 500-1000-1500-2500-2500

I would like to thank Gerald Agapov (Gerald) for his help in problems preparation, Filipp Rukhovich (DPR-pavlin) and Alexander Mashrabov (map) for round testing, Maria Belova (Delinur) for English statements and Mikhail Mirzayanov (MikeMirzayanov) for creation and development of Codeforces project.

This is going to be my third round on Codeforces, and I tried to make problems as interesting and diverse as possible. Hope you will enjoy this round. Best of luck! =)

UPD: round is over. Thanks for participating, hope you liked the problems.

Grats to all the winners:

Div. 1:

  1. tourist
  2. Petr
  3. rng_58
  4. al13n
  5. ecnerwal
  6. qwerty787788
  7. marek.cygan
  8. KADR
  9. Merkurev
  10. hos.lyric

Special respect goes to simonlindholm, the only participant to solve the hardest problem E!

Div. 2:

  1. matthew99
  2. acrrca
  3. ccdream
  4. cuber2460
  5. newSolars

Editorial is here.

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By narcis_vs3 weeks ago, In English,

Hello everyone,

I'd like to invite you to participate in a 2-hours Div2 round which will be held this Saturday, August 30th at 11:30 AM MSK. Div1 coders can take part out of competition, as usual. The problems were prepared by me and MirceaFF (B and C). I'd like to thank Gerald for helping preparation, MirceaFF for english translation and MikeMirzayanov for the Codeforces system.

The main characters of this round will be Caisa and Gargari,which have some interesting tasks for you. I hope you will enjoy the round. Good luck and have fun!

UPD: It will be used a standard scoring.

Here are the winners:






Stats about hacks can be found here.

Editorial is here.

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