The contest is over; I hope you've enjoyed it. 1465 participants submitted at least one problem correctly. Unfortunately, nobody managed to solve all 6 problems; congratulations to ShadowSong who won the contest by solving 5 first problems with the lowest penalty time!

290A - Mysterious strings

Last year we've verified that a lack of problem statement doesn't prevent participants from solving and submitting the problem successfully and at the same time saves the problem setter some writing effort. This year we've ascertained this again. Well, I could've invented a long and knotty legend about you, a young but very promising software developer, were summoned to White House and given a task of utmost importance: to deliver an interactive list of USA presidents from founding fathers to our days. It could have featured a dramatic time-consuming search for necessary info, pursuits, firefights, a wounded teammate whose dying words were "Eight is Van Buren, don't forget... print Van, just Buren... doesn't pass". But what for?

The contest editorial is available here.

Some jokes are fun only for the first time, repeating them makes them lose their charm. I certainly hope that April Fools Day Contest is not the case, but there's only one way to verify this :-) I'm happy to invite you to take part in the verification process which will take place on Monday April 1st. Let me disprove the suspicions some people have: the joke is the contest contents, not the fact of its existence or the lack of it — that would have been too simple :-)

In this round you'll face several weird problems and 2 hours to solve them. The contest will be unrated (you bet!), and it will follow ACM ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them). You can submit solutions in any language allowed by Codeforces. To get an idea of what awaits you, you can have a look at the last year's contest.

Be warned, to enjoy participation in this round you'll need a sense of humor compatible with mine! It's April Fools Day, after all. Good luck!

Upd. Registration is open till the end of the contest.

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!

We are growing and spreading! All-Russian Programming Championship CROC-2013 is followed after the Open Moscow Championship and the Championship for the Bauman MSTU Students.

The CROC company, with the help of Codeforces and Saratov State U, sets up a competition for the top talented programmers of the country. If you are a university student or a young specialist over 18 (and the citizen of Russian Federation), we invite you to participate. The first prize in the Championship is 100000 rubles, the second prize is 70000 rubles and the third prize is 50000 rubles.

Championship Schedule

*the championship can be expanded if the number of participants exceeds expectations, all finalists should to confirm invitation until May 2

• Qualification Round – April, 13-14
• Elimination Round 1 – April, 15 (up to 2000 participants)
• Elimination Round 2 – April, 22 (400 participants)
• The championship finals are going to take place on May, 16-17 in Moscow in the CROC office (50 participants)

The rules will be explained in more detail a little later, but no surprises are planned. We will try to involve the "out of competition participants" (that is, those who can't officially participate in the Championship) as much as possible.

Some pleasant surprise awaits for the participants in the dream office and outside it! The CROC company pays for the accommodation in Moscow during the finals. Also for Russian citizens the travel expenses around Russia will be covered (* The transport expenses outside Russia can be covered possibly partially but you need to contact us and clarify it for each particular case). The official event language is Russian, the problems will be in Russian and English.

Registration

To participate in the championship, you need to register on the championship page, website crocok.ru. The registration will be available until the qualification is completed. Compete with the best coders on an Open Programming Championship!

Register Now »

Hi all! This round was prepared by me and KAN. I hope, you will enjoy our problems.

I want to thank PavelKunyavskiy, who tested our problems, readed statements and so on. Moreover, alger95, Skird, fdoer, sand-martin tested round too, I thank them for it.

And of course, I thank Gerald for organising our work, MikeMirzayanov for the great system and Delinur for translation of the statements.

I hope, result will be better than results of our previous round. Good luck!

Pay attention, round will be held at unusual time.

Scoring:

div1: 500-1500-1500-2000-2500

div2 : 500-1500-1500-2500-2500

My congrutulations for leaders.

div1:

1. al13n
2. tomek
3. niyaznigmatul
4. voover
5. Egor
6. Zlobober
7. White_Bear
8. seanwu
9. wjmsbmr
10. peter50216

div2:

1. fotiIe96
2. zfmdhy786
3. wzc1995
4. gjh
5. mynameisverylong

Full english editorial: here

Good day, friends)

Welcome to regular Codeforces round #175 for Div.2 participants. Traditionally Div.1 participants can take part out of the competition.

The problems were again prepared by the group of authors: Pavel Kholkin (HolkinPV), Artem Rakhov (RAD), Fefer Ivan (Fefer_Ivan) and Gerald Agapov (Gerald). Traditionally thanks to Michael Mirzayanov (MikeMirzayanov) for Codeforces and Polygon systems and Mary Belova (Delinur) for translating the problems.

Score distribution is published in advance) today it is standard: 500, 1000, 1500, 2000, 2500.

We open the little secret of this competition, in all today's problems you find permutations)

We wish everyone good luck, successful hacks, high rating and good mood)

UPD1: the contest is over, hope you enjoy it)

UPD2: the tutorial is already published here)

UPD3: congratulations to winners:

1) hechuan
2) TroyI118
3) BekzhanKassenov
4) ahmed_aly
5) lxgsbqylbk

Hello everyone! Codeforces Round 174 will be held for both divisions on Sunday, March 17th at 7:30 PM MSK. The problem setters are abacadaea and me (scott_wu). We would like to thank Gerald for his help in preparing the contest and Delinur for translating the problems. We also thank MikeMirzayanov for creating such an awesome site. We are very excited as this is our first Codeforces round.

For this contest you’ll be helping Farmer John, Bessie, and the cows. We hope you enjoy the problems! :)

The score distribution will be slightly nonstandard.

Div2 — 500 — 1000 — 2000 — 2000 — 2500

Div1 — 1000 — 1000 — 1500 — 2000 — 2500

Good luck and happy coding! As always, to make the round more exciting, we recommend that you take a look at all the problems!

UPD: Our editorial can be found here. Thanks for participating!

Congratulations to the winners:

Div1

1. al13n
2. rng_58
3. HELEN_KK
4. wjmsbmr
5. bmerry

Div2

1. hockey_for_NOI
2. Efremov_licesos
3. Muali
4. koratel
5. lxfind

Hi all! :{

We're glad to invite you to participate in Codeforces Round #173 prepared by A.K.Goharshady, LGM and me (havaliza). I want to thank Gerald, MikeMirzayanov and Delinur who helped us to prepare the round on this platform. And thanks to dani1373, hhoomn, mruxim, MMJ and xorfire who tested the problems and helped us a lot.

Today is LGM's birthday and yesterday was gpac's birthday. Happy birthday to you guys! ^.^

Hope you enjoy today's round and have lots of fun. :)

Update. The editorial is out!

Hello there!

Codeforces Round #172 will take place on Sunday, March 10th at 19:30 MSK(23:30 CST).

This is my second time participating in prepration a Codeforces Round. Last time assist with YuukaKazami is an unforgettable experience. This time, the hardest problems were created by Jiatai Huang(CMHJT) and others by me and Yuping Luo(roosephu).

Testers are sevenkplus, YuukaKazami, pashka and Seter.

We gratefully acknowledge Gerald Agapov(Gerald) for his help in giving advise about the problems, Delinur for her help in translating the problems to Russian, and MikeMirzayanov, who has designed such a powerful platform.

Here let me express my personal thanks to the Codeforces community, which has given me so much gleamy idea in the past two years.

Believe it or not, Codeforces has kept her feet in China's ACM community since last year. AFAIK, some of the hardest problems have been used as this year's Winter Camp homework for our National Olympiad in Informatics.

Also thanks to watashi, ftiasch and xlk. Discussing problem with all of you, has inspired me a lot.

500 — 1000 — 1500 — 2000 — 2500.

We are going to use a standard score distribution in both divisions.

The problemset is a little bit easier than last time, but we still believe, getting all of those five problems accepeted will be a challenging mission even for an seasoned International Grandmaster. The problemset has been marriaged with variety flavor. Take a glance over all five problems before going to coding might be a wise strategy.

UPD:

The contest is over, congratulations to the winners:

Div1:

• UESTC_Nocturne
• liouzhou_101
• peter50216
• Petr
• Shik

Div2:

• antonio_junior
• kyuridenamida
• tsunayoshi
• ZJUT-Xixi
• bird5x

Congratulation to tclsm2012, who also solve the problem D!

We feel so pity to al13n, your last optimization for problem D is wrong. Problem D has a O(mklogn) algorithm. And we are extremely sorry to Jacob, your solution for problem E can pass most of the random tests but actually is wrong.

Jacob... can you explain your solution for us :)

We need collect some feedback about this round .. So the editorial will appear after a period of time.

UPD:

I used to hate those guys who set problems, but didn't write editorial at all! But when things turn to myself, I found it is really difficult to cover all cases. Anyway, it has been done.

Hello, friends)

Soon is coming regular Codeforces round #171 for Div.2 participants. Traditionally Div.1 participants can take part out of the competition.

Again and again the problems were prepared by the familiar group of authors: Pavel Kholkin (HolkinPV), Igor Kudryashov (Igor_Kudryashov), Nikolay Kuznetsov (NALP) and Gerald Agapov (Gerald). Traditionally thanks to Michael Mirzayanov (MikeMirzayanov) for Codeforces and Polygon systems and Mary Belova (Delinur) for translating the problems.

UPD: score distribution will be not standard a little bit: 500, 1000, 1500, 2000, 2000.

We wish everyone good luck, successful hacks, high rating and good mood)

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

Congratulations to winners:

1) study_english
2) ipip2005
3) rng_50216
4) bfrcns197
5) csavky103

UPD3: the editorial will be published soon