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

Hi everyone!

Codeforces Round #170 begins soon, and I'll be the problem setter. I hope many people will be happy to solve all the problems.

UPD: The scoring is dynamic. The problems are sorted by increasing of estimated difficulty.

And the standard part: thanks to Gerald for his help with the problems, Seyaua and sdya for testing the contest, Delinur for translations, MikeMirzayanov for building the Codeforces platform.

Good luck!

UPD: Tutorial

Good Day!

The next Codeforces round will start soon. It will be held by usual Codeforces round rules.

The author of today's round is Mykhailo Granik (Fcdkbear), he is listening the lecture at the Winter Kharkiv Programming School now. Great thank him for this contest!

The score distribution will be standart: 500-1000-1500-2000-2500.

Good luck to all!

Hi everybody! :)

Codeforces Round #168 will start in hours. haas and I (havaliza) are the authors of today's match. I'd like to thank Gerald and Delinur for helping us to prepare this contest and MikeMirzayanov for this great platform.

Hope you enjoy solving the problems as much as we enjoyed preparing them. ^.^

Good luck and have fun. :)

UPD1.

Score distribution will be:

Div2 = standard

Div1 = 500-1000-1500-2000-2000

UPD2.

Congratulations to the winners of both divisions. It's nice that after the contest all five winners of first division are red coders and all winners of the second division are first division coders!

Div1:

1. rng_58
2. Petr
3. Komaki
4. msg555
5. maksay

Div2:

1. qph-Jeremy
2. dojiboy9
3. FreezingCool
4. Hellis
5. yplusplusplusplus

Editorial is out and will be completed soon. :)

Before leaving Tehran I asked SeMeKh a couple of questions on how the training for the competitions works in Iran.

There are local and regional Olympiads in Informatics in Iran which take place across the whole country. Top 40 winners will get together in so-called Golden Camp and train the whole summer, with a break of 2-3 weeks in Ramadan, so the camp duration exceeds 2 months. Part of the participants with lowest scores leave the camp earlier. The rating of participants is classified as either gold, silver, or bronze. "Golden" participants get the right to enter any university in the country without Concur. The 4 participants of IOI are also selected from the "gold" category. Please note, that there is no national Olympiad in Informatics. — see note below.

Iranian competitors achieved following results in the International Olympiad in Informatics:

• 2012, Italy — two gold (mR.ilchi, havaliza), two silver (LGM, mruxim) medals.
• 2011, Thailand — three silver (including SeMeKh and sajad22), one bronze (kasnavi) medal.
• 2010, Canada — gold (a70babat), two silver (Mehrdad, SeMeKh), one bronze medal.
• 2009, Bulgaria — gold (a70babat) and three silver (including pooya_, Solej) medals.
• 2008 — unfortunately, Egypt didn't grant visas to the team of Iran.
• 2007, Croatia — gold and three silver (including Saeed_Reza) medals.

As you can see, results are very high, all 4 pupils normally get medals, there is often a gold one. Many organizations support and organize high school students for comptetion, which is unfortunately not the case with university students. I have not heard of a well-organized system of training for ACM ICPC in the country. Hopefully, the situation with support from universities, government and business will change, and I suspect it is a local business who will initiate the change.

There were not enough time to discover more details, so I will be happy to here rich comments from Iranians on the topic as well as tough questions from everyone interested.

UPD. Please see important comment from A.K.Goharshady below.

UPD 2. Here are some numbers from inoi.ir. There are about 10000 participants in the first stage. About 1000-2000 qualify to the second stage, which is a two-day event which includes multiple-choice test and a kind of examination. Some 60-70 people go to the stage where they solve problems using a computer, 35-40 summer camp participants will be selected here. There are 8 gold medalists at the camp, 4 of which will then take part in IOI.