Welcome to 2013-2014 CT S01E04: 2013 Kashan Contest + Some Problems of 2009 Google Code Jam World Finals (GCJ WF 2009). The training duration is 5 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.

The registration will be available on the Gym page and will be opened until the end of the training. Be careful registering team: please, choose only whose members who will take part in the contest.

The most problems were given by mohammadrdeh. Thanks! It is the great help. Take example!

Good luck!

Recently we’ve changed the contribution formula. Now it reflects the current social activity, that’s why all votes for posts and comments are divided by two every 180 days. On the one hand it helps to distinguish the currently active Codeforces members, on the other hand it makes the contribution top more dynamic and opened for the newcomers.

For example, now Egor is the leader of the contribution top because of the (mostly) many interesting posts about ACM-ICPC World Finals. But it looks like 9 months after the World Finals, he can loose the first place.

Also I’ve made some changes with the votes:

1. Now the negative score is not shown (just 0) if it is in range [-5,-1]. I did it because many of you downvote just because you see the negative score.
2. Visualization of vote in comments.
3. Changed some rules to transform votes to contribution, but it is a monotonic function anyway.
4. A comment becomes partially transparent if it has -10 or less (it was -5).
5. A comment becomes hidden with the message about too negative feedback if it has -25 or less (it was -10).

I hope you we will do same changes as in items 1-2 for posts.

Welcome to 2013-2014 CT S01E03: selected problems from 2002 Central European (CEPC 2002) + 2010 Southeast USA Region. The training duration is 5 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.

The registration will be available on the Gym page and will be opened until the end of the training. Be careful registering team: please, choose only whose members who will take part in the contest.

Good luck!

Welcome to 2013-2014 CT S01E02: Extended 2003 ACM-ICPC East Central North America Regional Contest (ECNA 2003). The training duration is 5 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.

The registration is available on the Gym page and will be opened until the end of the training. Be careful registering team: please, choose only whose members who will take part in the contest.

Good luck!

Welcome to 2013-2014 CT S01E01: Extended 2000 ACM-ICPC East Central North America Regional Contest (ECNA 2000). The training duration is 5 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!

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 at about 12:10 PM (UTC), which is 16:10 Moscow Time. 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 practice takes place on September, 11, at about 12:10 PM (UTC).

With the help of some experienced and respected members of the community (thanks!) there was formulated a rule that allows a third party code to be used under certain conditions. Please read carefully the text.

The following text will go as part of a renewed competition rules. The closest contest will be held already on the updated rules. Thus, there are about two days for further details, if something is unclear.

Solutions and test generators can only use source code completely written by you, with the following two exceptions:

1. the code was written and published/distributed before the start of the round,
2. the code is generated using tools that were written and published/distributed before the start of the round.

Any usage of third-party code should not violate the right holder’s license or copyright. Remember that published code is not always free to use! At the request of the right holder, any code that violates the license or copyright may be considered as violating the rules.

All the changes in the code from exceptions 1) and/or 2) must be made solely by you.

If there are any doubts about the time of publication, possible collaboration etc., a participant will have to prove his/her complete innocence by presenting compelling and satisfactory evidence.

Currently, the only reliable proof is the presence of code on the Internet and the presence of the used edition in the cache of well-known search engines.

For example, this rule accepts the use of the code from the website http://e-maxx.ru/ if the code was written and published/distributed before the start of the round. With the help of search engine caches, it can be easily shown that such code doesn't violate the rules. Similarly, it is permissible to use the code from a book/article that was published before the contest. On the other hand, using team reference code (for example, prepared for ACM-ICPC World Finals) is not allowed if there is no reliable and objective way to prove that the code was written before the contest.

This rule doesn't loosen the rules about prohibiting of communication, discussion, or any other form of communication between the contestants on any topics about the problems during the round.

Rah-rah!

We are moving forward to accelerate testing. In fact, when our rounds attract 3500+ registrations, it is hard to test all the submissions on nine computers "Core 2 Duo E6750, 2.66 Ghz, 3Gb".

Computer Science Department of Saratov State U has recently got 20 new computers i5-3470, 8Gb. After a little research it was found that if boost CPU to 3.5Ghz (of course, turning off all sorts of turbo boost and after many hours of stability check), the speed is approximately equal to twice the speed of the old testing machines. This is very convenient as it will in future only to divide all the time constraints in the problems by 2.

We have moved to testing on new computers and we do it in compatibility mode. This means that all the time constraints before the start of the program are divided into 2, the program is executed, and at the end a running time is multiplied by 2. In fact, if you do not use the cut-off by time or some other unsavory stunts, you will not detect any changes.

Old testing machines are switched off now.

To be very precise, the new computers are not so fast as 2x old. That is in compatibility mode it is normal to notice a slight degradation in speed.

ABBYY Cup 3.0 — Finals is about to begin. We wish good luck to all the participants!

You may view the current contest standings here.

We do not want the rest to get bored. So ABBYY and Codeforces conduct an unofficial online version of the contest today at 15:30 UTC.

This round will be:

• rated
• for both Div.1 and Div.2
• 2 hours duration
• on the modified ACM ICPC rules (problems are divided into subproblems, count only complete solutions of subproblems, there is a score for each subproblem, a penalty is charged by the rules of ACM ICPC)

Good luck!

Hello.

If you are not sleeping now, join to Testing Round 8. Thanks!

Thank you for participation. See you tomorrow on MemSQL start[c]up Round 1.

Our community keeps on growing and gaining in popularity! We are glad to announce that Codeforces has recently registered its one hundred thousandth user. Thanks to everybody who keeps the project going — the problem writers, testers, corporate partners and of course all members of the community. Our special gratitude is to the VK.com company!

One cannot get enough of the good statistics. Here are some more numbers:

• our database contains more than 3.5 millions of your submitted solutions,
• the number of problems comes near 3000,
• the number of site visitors per month excedes 400000,
• the number of page views per month amounts is approximately 5000000.

The first information letter

General information

In the first part of August 2013 Saratov State University runs an international student summer school in computer programming. The exact dates are 5-15 of August. Teams of three people and individual participants are invited to take part in it.

The school will take place in a picturesque place at one of Saratov resort centers on the Volga bank. The participants will be provided comfortable rooms for 2-4 people and meals three times a day. The resort center owns a beach and sport grounds.

It will be 10 training days. The school includes lectures by Saratov state university coaches, joint trainings, problems tutorials and topical workshops. The curriculum is designed for younger university students who aspire to achieve high results at programming competitions. Official language is Russian.

The fees are 16500 RUR (~ 525 USD) per a person. Moreover, each team or an individual participant should bring a laptop with the support of WI-FI.

All interested participants and teams should register at http://goo.gl/DHwqU till 15th June 2013. Don't postpone the registration, as the number of participants we can take is limited.

You can get additional information by e-mail mirzayanovmr[symbol-at]gmail.com. As since the official language of the school is Russian, the registration requires knowledge of Russian. Also it is recommended to view this page in Russian.

You remember the cool promotional videos (in Russian) on the All-Russian Open Programming CROC 2013 Championship, right? This time CROC amazed us and sent us an after-the-championship video. Someone here might find him/herself in the video and someone just might be interested to see the way it was.

Besides, there is a complete photo archive.

In conclusion, I am glad to use this opportunity to describe my excitement at the way CROC works, their attitude towards the event, their professionalism and the achieved work! It was fun and easy to work together :) Our special gratitude goes to Sergey Strelkov, Georgy Mogelashvili and Maria Dovzhenko.

Today it will be Croc Champ 2013 Finals! Good luck to all participants. And to those who don't participate — enjoy the interesting competition.

Yesterday have finished the trial contest and Code Game Challenge. The winner of Code Game Challenge is ... tourist!

Also pay attention to the Croc Champ 2013 - Finals (online version, Div. 1). It will be a rated round. Note: it will be slightly unsual because we will not hide the standings of the official contest. So some information about difficulties of the problems will be known before the round. The contest duration is 2.5 hours.

Good luck to everyone!

The contest has been finished. The winners are:

• tourist
• Egor
• eatmore

Final standings

Actually me and MaximShipko have arrived yesterday.

During this time we, together with CROC staff, had setup 40 computers in the classroom (so it is pity that most of you will use own laptops), installed Code Game Challenge infrastructure and ready to meet the participants.

Soon it will be [contest:307]. Do not worry it some of the website features will be disable, our main goal is to make onsite-event.

Note that today the participants will take part in unofficial entertaining AI-programming contest.

I'll greet all the participants personally, and now I'm sending rays of sadness to the participants, who will not be able to participate today because of the curriculum.

Testing Round 6 starts on May 11, 2013, 20:00 (UTC). Our goal is to test the platform after recent improvements. All of them are in the Codeforces backend, but they affect many lines of the code.

I invite you to take part in the round. It will be Div. 2 + unofficials from Div. 1. It will contain four-five obsolescent problems. But I think it will be interesting for many of you. The problems contain very weak pretests to force more hacks. It will be unrated round.

Many thanks to participants!

P.S. As it is testing round, we do not guarantee stable work and so on.

Hooray! Yupee! We have finished the complex me-Cormen-ralekseenkov logistic combination and now are ready to pay tribute to the heroes of 2012. This year (thanks, Thomas!) the Cormen Medal laureates are going to get a new Thomas Cormen book "Algorithms Unlocked", signed by the author in addition to the medal, glory and fame!

The 2012 Cormen Medal laureates are:

• tourist (Gennady Korotkevich) — Codeforces Best Coder 2012
  Gennady keeps his first place in the Codeforces rating, continues participating actively and at this point the third place in the round isn’t always a rating improvement for him. We wish Gennady more victories, especially considering that the ACM-ICPC 2013 Finals are so soon!
• witua (Vitaliy Herasymiv) — Codeforces Best Problemsetter 2012
  In 2012 Vitaly dazed us with his interesting problems many times. Due to him, we are experts on all sorts of lucky number and Little Elephant properties. Thanks to Vitaly for the great problems!
• Nickolas (Mariia Mykhailova) — Codeforces Spirit of Community 2012
  Maria, the author of unusual rounds, an active blogger of 2012, has received a new nomination. Maria’s ideas, bright and out-of-the-box, have made the live of the community more diverse and fun.
• Alex_KPR (Alexander Kouprin) – Codeforces Best Blogger 2012
  We all love reading Alex Kouprin’s stories from all sorts of 2012 sports programming events.

Let us remind you that it’s the third year when the Cormen medals has been awarded. It’s the third year when [tourist] has become the best coder and Alex_KPR — the best blogger twice in a row. My favorite nomination, "Codeforces best problemsetter" went to natalia (Natalia Bondarenko) in 2010, and to Ripatti Artem Ripatti in 2011.

We do hope that the last year laureates will amaze us with their talents on in 2013.

As you probably know there are International Workers' Day holidays in Russia in the beginning of May. Am I the only person who see a contradiction here? Workers and continuous holydays!

So I decided that the best way to spend May, 2nd is to do something useful. So meet new languages on Codeforces:

• Python 3 (3.3.1)
• MS C# .NET 4
• Go (1.1 RC1)

Also I made an attempt to setup Clojure, but his AOT nature makes any solution (even A+B) to run for at least 1 second :( I believe it is possible to precompile Clojure solution into bytecode, but I haven't found the way yet. Maybe someone can help me?

There are three days before round. Three days to test new languages. Please write comments in case of any issues.

P.S. As extra bonus — I've updated Python 2 to 2.7.4.

Hi everybody!

Let me remind you that on the 12th of April, at 20:00 the Qualification Round of the All-Russian Programming Championship CROC-2013 will start.

You need to participate in the Qualification Round to make it to Round 1. Contestants who gain a score equal to the 2000-th place finisher score or greater will advance to the Round 1 (also you need to gain positive score).

At the Qualification Round you will find a few problems, roughly ordered by the increasing complexity. During the Qualification Round the problems are judged only on pretests and system testing will take place after the end of the Qualification Round (round continues for 48 hours). The pretests do not cover all possible cases of input data, test your programs carefully! The Qualification Round has no hacks or decreasing values of the problems.

The round will last for 48 hours, but it does not mean that we encourage you to spend all this time solving of problems. We hope that most participants will cope with the problems (or with most problems) in a shorter period of time. This duration of the round is chosen so that each participant could find a convenient time to participate.

Before the end of the round it is strictly forbidden to publish the problem statements/solutions/any thoughts and ideas about them elsewhere. It is forbidden to talk about the problems, discuss the statements and so on. Be honest and let the best men make it into Round 1. When the Qualification Round is over, you can discuss the problems and solutions.

You can register for the round at any time up to its end.

The results of the round will not affect the rating, non-competitive participation in the round is not allowed. However, all tasks will go to the archive after the end of the round.

Best of luck and enjoy solving the problems!

P.S. You can't take part here unofficially. You may register to the Championship here. The working language of the Championship is Russian, but all the problems will be in English too.

Most agile participants have registered before we implemented validation rules around Championship registration. So some registrations will be canceled. Sorry for it — you may register to the Champ and register for round after it.

UPD: Testing is completed. Unofficially qualification cut-off is 950. Participants with at least 950 points advance to Round 1. It can be changed because of cheaters disqualifications.

As the TopCoder TCO 2013 Round 2A did not take place as planned but was moved (with sniper precision) right on the place of the Codeforces Round #177, we decided to reschedule the contest. I have to admit that my first urge was to leave everything as it is — TopCoder knew of Codeforces Round 177 and I cannot approve of such an approach to solving their technical issues. On the other hand, no fault lies on the community, and especially on dear witua, the writer of the forthcoming round. You’d like to participate and the writer is keen on making a round as popular as it gets. Besides, the problem coordinator Gerald would have fallen under much pressure, juggling work and TCO. That’s why the Codeforces Round #177 moves to the time that was initially planned for Round 178, and Round 178 moves a little ahead.

We apologize for the schedule inconveniences and hope to see you among the Codeforces Round #177 participants. It will be fun!