There were a lot of requests like "Russian team ioi-2013 blog". I'll try to write something. This year I am a guest on IOI, so I have a schedule that differs from the contestants' one. For example, when the contestants had the Practice Session, where, as rumoured, there were something bad with printers (but do you remember at least one place where printers worked good from the beginning? ;), I had an excursion to Lone Pine Koala Sanctuary, where are some beautiful Australian (but not only) animals, for example the following ones:

Welcome to another Codeforces Round!

Please note that the time of round #191 was changed. Contest will start at Thursday 12:30 UTC.

My name is Linh (ll931110). I'm from Vietnam, and I'm glad to present to you my first Codeforces round. It is for Div 2 only; however, I welcome participants from Div. 1 to participate and enjoy challenging problems. I hope this would be a pleasant gift for those who are going to IOI 2013 (and participants from World Finals), which will take place in just a couple of days.

This round is prepared by me and fchirica (from Romania). Also, I would like to thank the Codeforces team who puts efforts on making Codeforces and Polygon possible.

Happy solving!

UPD1: The score of problems in this round will be dynamic. The problems will be sorted in increasing difficulty order, at least in our perspective.

UPD2: The contest is over! Congratulations for everybody, especially for those who solved E. You proved to be smarter than I am (your solutions were totally unexpected to us). Thank Gerald, Aksenov239 and Delinur for helping us on preparing the round!

Div. 2 winners:

1. SillyHook02

2. Tsukiko

3. Quit_Quickly

4. Zhengxu

5. sevenzplus

Those are five people who nail all problems!

Unofficial winners:

1. Kissshot

2. R_R_

3. xchernoff

4. wakaka

5. phtniit

The editorial will be completed soon after revising and adding possible alternative solutions. You are welcome to post your answers in comments.

Thank you and see you in the next round!

UPD3: Editorial is now available. Remind that it is not the final version, as we are writing possible alternative solutions for problems. Stay tuned!

UPD4: Editorial is now completed.

15:24 — Closing ceremony will start shortly and you can watch it on ICPC Live. That's probably it for this translation. Bye-bye, see you soon

A live scoreboard for the ACM ICPC 2013 world finals will be available here: http://ahmed-aly.com/ICPC.jsp

This is just a sample for how it will look like, I might make some small modifications.

The scoreboard displays many information about each team, like the university, the country, the region, the team name, the members TopCoder handles, the members real names and the coach name. Also you will be able to filter the scoreboard by the region or the country. And the scoreboard highlights the champion for each region and shows some icons for the cup and the medals winners.

Edit 1: I added a chatting widget (you can hide it), and the practice contest scoreboard is available now.

Edit 2: Now you can pin your favorite teams to the top of the scoreboard, and you can hide some columns, and there are some statistics rows in the bottom of the scoreboard.

Edit 3: Here is the final ACM ICPC 2013 world finals scoreboard: http://ahmed-aly.com/ICPC.jsp

Hello, everyone!

Do you want to train your skill by a contest before ACM/ICPC Finals?

Codeforces Round #190 will take place on Friday, June 28th at 19:30 MSK. This is the last chance to practice, don't miss it!

I am cgy4ever from China, and this is my first round on Codeforces, I hope you will love it.

As usual, there will be 7 problems: 2 for Div2, 2 for Div1 and 3 for both. I am the writer of them. And I would like to thank Gerald and sdya for testing, and MikeMirzayanov for the Codeforces project including polygon system.

Good luck and have fun!

Update 1: The score distribution for Both Division is regular (500-1000-1500-2000-2500). The main character of all problem will be: Fox Ciel. (See here for more info)

Update 2: Also thanks Aksenov239 for helping prepared this round, including translate the problem statement into Russian. And I'm sorry for the delay of judgement at the beginning of this round. Fortunately it goes better now.

Update 3: I have write a draft of editorial for this round when you are solving problems.

You can read it here.

Note that I didn't do any proof read and there are some typesetting issue. Anyway, I will improve it and this version is just for someone who is urgent to know the intended solutions.

Update 4 Contest complete! This round will be rated!

Congratulations to the winners:

Div2:

1. Baklazan

2. phidnight

3. kingofnumbers

4. pawel.jasinski1986

5. Ronnoc

Div1:

1. YuukaKazami

2. rng_58

3. Egor

4. tmt514

5. chnlich

And after this round, ivan.metelsky becomes our new International Grandmaster!

June 27 is an important date – that’s when the test round of Yandex.Algorithm kicks off. Don’t miss your chance to register, so you can be in the running for a place in the final round, which takes place on August 21-23, 2013 in St. Petersburg. The final round venue is truly unusual for such an IT event – the palace of Grand Duke Vladimir, built in 1870, will welcome finalists with all its historical charm.

In the final round, the best participants will be left one-on-one with the testing system – no internet connection or prewritten code, only properly set-up computers and IDEs. We will provide text coverage of the round.

If you want to be part of the action, don’t leave your registration to the last minute – remember, the test round starts tomorrow.

More good news: we decided to almost double the number of T-shirts. The best 75 non-finalists among participants of the elimination stage, another 75 random participants of the elimination stage who successfully submit a correct solution to at least one problem and, of course, all finalists will receive an exclusive Yandex.Algorithm T-shirt.

UPD: The test round is available for participants now: http://algorithm.contest.yandex.com/contest/306.

Current standings are open for everyone: http://algorithm.contest.yandex.com/contest/306/standings.

UPD2: Official results are avaliable on the official website

UPD3: Round archive is avaliable at the official website

Hello, Codeforces! :-{D

As two important events IOI and ACM ICPC are coming soon, me and my friends as the Iranian IOI team decided to prepare a gift for all the Codeforces users who'll soon participate in one of these events, and also everybody else. :)

This round authored by me (havaliza), dani1373 and keivan with help from fab. I want to thank all the Codeforces team for their kind and great effort to maintain this website.

Hope you enjoy solving the problems as much as we're enjoying preparing them! ^.^

Update 1. The score distribution for Div. 1 is 500-1000-1500-2500-2500 and for Div. 2 its regular.

Update 2. Special thanks to Aksenov239 who helped us so much to prepare this round.

Update 3. Here is the editorial. To be completed soon :)

MemSQL is happy to announce start[c]up -- a programming competition, hosted by Codeforces and MemSQL HQ located in San Francisco, California. start[c]up consists of two rounds.

All rounds will be prepared by MemSQL engineers: pieguy, nika, exod40, SkidanovAlex and dolphinigle.

Round 1 is online and takes place on July 13. Round 1 follows regular Codeforces rules and consists of 5 problems. For this round, the complexity of the problems will be comparable to a regular Codeforces round. There are no eligibility restrictions to participate in the round.

Round 2 takes place on August 3, consists of 5 problems, and uses regular Codeforces rules. The complexity of the problems is higher than a regular Codeforces round. Only people who finished in the top 500 in Round 1 can participate. The top 100 in round 2 will receive a start[c]up T-shirt.

For the Silicon Valley residents, MemSQL will be hosting up to 25 people on-site during the second round. The winner of the on-site round will be awarded a special prize.

MemSQL is building an in-memory database that powers many well-known companies, such as Morgan Stanley and Zynga. Nearly half of our engineers are TopCoder Open Algorithm finalists in recent years, and we have more IOI and ICPC medals than we have engineers.

The reason for such a skew towards topcoders is that only very good engineers can build a database. Even though topcoders might not have skills necessary to build a database, they are known to be very smart. We’ve seen that smart coders can quickly acquire necessary skills, but average coders, regardless of experience, cannot learn to be smart.

We have lots of exciting problems for topcoders. For example SQL Query optimizer, cluster management for the distributed system, lockfree storage engine were all written by topcoders in here. If you are looking for an internship or for a full-time position and want to work on exciting stuff with people who are as smart as yourself, send your resume to topcoder@memsql.com.

Good afternoon, Codeforces!

Today I'll tell you about a new feature of Polygon system, which is used to prepare all Codeforces rounds. Of course the system is open to any user – many contests for other competitions and training camps are prepared there.

Two key elements of a problem, besides the author's solution, tests and statements, are two programs: the validator and the checker.

The validator is the program that reads the test and reports whether it corresponds to the condition of a problem or not. Validators must be absolutely formal – a validator validates a test if and only if it meets the conditions of the problem and can be safely added to the test set. You can easily write validators using the testlib.h library. Sometimes authors neglect validators (which never happens during the Codeforces contests) and it threatens the validity of tests. Since the Codeforces contests contain hacks, the importance of correct validator greatly increases. Naturally, all the hacks are validated before reaching a contestant’s solution. Most tasks have relatively simple validators, but when a problem contains additional conditions (for example, that there is a solution for the test), then the complexity of the validator is greatly increased.

The checker is the program that receives the test, the output of the participant’s code, the output of the jury’s code and determines the correctness of the participant’s output. Unfortunately, errors in the checker often lead to serious consequences. Not all problems let you simply compare the solutions. For example, in problem 234H - Merging Two Decks the checker uses a Cartesian tree. If the problem statement requires a certificate, then it’s a good idea to write the checker in the concept of readAnswer(ans)/readAnswer(ouf). You can easily write checkers using the testlib.h library.

Testing of these programs usually takes place either manually from the command line or indirectly — by adding wrong solutions and temporarily adding of non-valid tests. In fact, the authors often neglect to test checkers and validators. This method of testing is inconvenient, and the tests are not saved. When there are two authors cooperating, a co-author cannot view the tests, on which the validator/checker were tested, or restart them after the correction of the validator or checker.

The updated version of Polygon has improved immensely! We’ve made a convenient means for testing the validator and the checker.

Hello, friends!

Winter 188th Codeforces Round is coming!

We wished to prepare for you some enjoyable problems (as we believe, not very difficult) with nice ideas and clear statements.

"We" includes authors of the problems yaro and Rei, Codeforces Rounds supervisor Gerald and the platform founder MikeMirzayanov. Special thanks to Pasha (PavelKunyavskiy) and Artem (RAD) for the testing and helpful comments.

Last time I was preparing a competition here on Codeforces, Rounds were still "beta". Well, with less "beta" comes greater responsibility. So I wish the authors and the organizers a successfully held Round. As for the participants, I wish you the unconventional ideas, the clean code (and a clean keyboard, of course), and satisfaction from five (well, possibly the less number will also do...) correct and accepted solutions!

It seems to us that it is not an easy job to arrange the problems by their difficulty, so we have chosen the dynamic scores. Still (out of curiousity) let us put a bet on the following relative difficulties for the problems: div.1 — B-B-C-C-E, div.2 — A-B-C-C-E. How close is our guess?

UPD Sorry for the problems with the Codeforces testing queue during the round.

We will still be happy if you rate our contest (when it will be over): short survey.

And with the gap of one hack the winner of div.1 is meret (Jakub Pachocki)!

Div.1 standings, Div.2 standings.

Analysis (thanks to Rei for the translation).