Hi everybody,

Less than in 30 minutes there will start a second round of IOI 2017. Yesterday all the students visited the sixth talles tower in the world named Milad Tower.

We wish all the contestants the good luck!

Some useful links (more to be added):

• First round discussion.
• Official rankings.- Таблица реузльтатов от неутомимого snarknews с множеством разной дополнительной интересной информации.
• Rankings by snarknews with lots of extra interesting information.
• List of the contestants according to the great IOI database.
• IOI website
• Post by SeyedParsa about the Olympiad.
• Mirror contest hosted by Yandex.Contest.

Hi!

On Monday, July 31, 2017, at 14:35 UTC rated Codeforces Round #427 for participants from the second division will take place. As always, participants from the first division can take part out of competition.

The problems for this round were prepared by me. Many thanks to Alexey Ilyukhov (Livace) for help in preparations of the round and testing the problems, AmirReza PoorAkhavan (Arpa) for proofreading the statements and testing the problems, Gaev Alexandr (krock21) for testing the problems, Nikolay Kalinin (KAN) for the round coordination and, of course, Mike Mirzayanov (MikeMirzayanov) for great Codeforces and Polygon platforms.

The round will last for 2 hours, and you will be given 6 problems. I recommend you to read the statements of all problems. I hope everyone will find an interesting problem!

Scoring will be announced before the round.

Scoring: 500 — 750 — 1250 — 1500 — 2250 — 2250.

UPD.

Thanks for participating!

The editorial is here.

Congratulations to the winners!

Div2:

1. ywwyww

2. nick452

3. JustAnAverageCoder123

4. cxt

5. wa1tz7I9

Div1:

1. dotorya

2. rajat1603

3. anta

4. Kaban-5

5. HellKitsune

Hello, fellow programming contest enthusiasts!

We are pleased to invite you to take part in the forthcoming Codeforces Round #426, which is going to be held at Sunday, 17:35 MSK. In case one of the things you fear most is a Codeforces round being authored by a purple guy, we've got some badgood news for you: this round will feature two CMs – me (xen) and GreenGrape – as its writers!

The classic Codeforces rules will be applied to this round. There will be five problems for each division, with three of them shared by both. The round will last for two hours. Forgoing a long-standing Codeforces tradition, we will not have the scoring disclosed until shortly before the contest.

In this round, you are going to assist Slastyona the Sweetmaid – a renowned lover of sweets, cupcakes, candies and all other kinds of confectionery! In her everyday life, Slastyona often faces challenging problems, some of which cannot be solved without your help.

Kudos to our testers: Kirill Seemann Simonov, Evgeny rek Tushkanov, Yegor Voudy Spirin, Evgeny WHITE2302 Belykh, Vladislav winger Isenbaev and Alexander AlexFetisov Fetisov. We would also like to thank Arthur tunyash Riazanov for his ideas on some of the problems. Thanks to the Codeforces coordinator Nikolay KAN Kalinin for his assistance in making this round happen (and for his patience, too), and, of course, to the one and only Mike MikeMirzayanov Mirzayanov for creating the magnificent Codeforces and Polygon!

You may ask: “Is it rated?” Well, for what's it worth, it seems it is, since we've commited all our passion and efforts to prevent the contrary :)

In any case, we wish you luck/bugfree code/high rating/whatever and hope that solving our problems would be a great pastime for you on this lovely Sunday evening.

UPD. The scoring is:
Div. 1: 500 – 1250 – 1500 – 2250 – 2500
Div. 2: 500 – 1000 – 1500 – 2250 – 2500

UPD 2. Our congratulations to the winners!

Div. 1:

1. Radewoosh
2. LHiC
3. VivaciousAubergine
4. SanSiroWaltz
5. W4yneb0t

Div. 2:

1. nguyenthibanh
2. ColdSu
3. LLX
4. EnjoyCallen
5. pr3pony

UPD 3. Editorial

artwork by Ilya Shapovalov

Hi everybody!

I am writing this post from a sunny Tehran where the 29th International Olympiad in Informatics is being held. Me and Mikhail Endagorion Tikhomirov are here as a part of Russian Federation delegation on the Olympiad.

In about four hours the first round of the main competitive programming school student event of the year starts. Russian Federation is presented by one of the youngest team ever in the history of Russia on IOI consisting of:
Vladimir voidmax Romanov, Denis Denisson Shpakovskiy, Alexandra demon1999 Drozdova and Egor Egor.Lifar Lifar.

In Russian version of this post me together with Endagorion are going to make a text coverage of what is happening on the contest. We will mainly concentrate on Russian delegation there, so we are not going to duplicate all the live information in the English version of the post, but we invite all of you who are interested in IOI to discuss the problems and the results in the comments section below.

SPOILER ALERT: the text of this post and the comments may possibly contain lots of spoilers to the competition problems, so if you are going to participate in any online mirror, or you simply want to solve the problems buy yourself then be careful.

PS Some photos with comments in Russian are available at the Telegram channel here.

Some useful links (more to be added):

• Rankings by snarknews with lots of extra interesting information.
• List of the contestants according to the great IOI database.
• IOI website
• Post by SeyedParsa about the Olympiad.
• Mirror contest hosted by Yandex.Contest.

Hello, Codeforces!

The latest innovation in Codeforces is introduction Google calendar with information about the upcoming contests. To view calendar you can visit tab "Calendar" in the top menu.

The Codeforces contests are adding in calendar automatically. Also you can add contests from the other programming platforms. Each red user has this option. In addition, we will grant the rights to edit the calendar to employees/enthusiasts of other popular platforms.

In the tab "Add" you can add information about upcoming contest. The form shown below will help you for this.

Please, add to the calendar classic algorithmic contests which duration does not exceed a day. Also the contest must be publicly available, i. e. had English statements and open for a wide range of participants. We ask you to use short names for competitions, as it is presented in the examples, for convenience and uniformity.

Also you can edit or remove information about upcoming events in corresponding tabs.

We hope that the calendar will be useful for you and will help to planning your time and learn about all upcoming programming events.

In our plans to expand the functionality of the calendar. Write about your ideas for improving it in the comments.

Hello Codeforces!

On July 24, в 17:35 MSK rated Codeforces Round #425 (Div. 2) will be held. As always, participants from the first division can take part out of competition.

This is my first round. Many thanks to Nikolay Kalinin (KAN) and Alexey Ilyukhov (Livace) for help in preparations of the round, Ildar Gainullin (300iq), Daniil Nikolenko (qoo2p5) and AmirReza PoorAkhavan (Arpa) for testing problems and also to Mike Mirzayanov (MikeMirzayanov) for Codeforces and Polygon platforms.

You will be given 5 problems and 2 hours to solve them. Scoring will be announced before the round.

I hope you'll enjoy my round. I wish everyone good luck and high rating!

UPD1: The scoring for this round is: 500 — 1000 — 1750 — 2000 — 2500.

UPD2: Congratulations to the winners! Editorial here.

Div.2 :

1. LGTwins

2. nick452

3. Torta

4. ez_zjt

5. Parachutes

Div.1 :

1. TimonKnigge

2. Um_nik

3. quailty

4. dotorya

5. Kaban-5

Hello Codeforces!

On July 16, 18:05 MSK Educational Codeforces Round 25 will start.

Series of Educational Rounds continue being held as Harbour.Space University initiative! You can read the details about the cooperation between Harbour.Space University and Codeforces in the blog post.

The round will be unrated for all users and will be held on extented ACM ICPC rules. After the end of the contest you will have one day to hack any solution you want. You will have access to copy any solution and test it locally.

You will be given 7 problems and 2 hours to solve them.

The problems were prepared by Ivan BledDest Androsov and me.

Good luck to all participants!

UPD: The editorial can be found here.

Congratulations to the winners:

Congratulations to the best hackers:

929 successful hacks and 587 unsuccessful hacks were made in total!

And finally people who were the first to solve each problem:

Hi!

On Thursday, July 13, 2017, at 15:05 UTC Codeforces Round #424 will be held. Some of the problems will be from VK Cup 2017 Finals, some are prepared by Codeforces team to complete the problemset.

There will be six problems in the second division, five as usual in the first, three of them shared. The problems of this round are proposed, prepared and tested by: send_nodes, akvasha, ilya_the_lamer, fcspartakm, Perforator, MikeMirzayanov, PavelKunyavskiy, qwerty787788, Belonogov, izban, tourist, vepifanov, AlexFetisov, winger, Errichto, Gassa, naagi, ashmelev, Endagorion, ifsmirnov, Arterm and me. Huge thanks to all who helped with the preparation!

There will be prizes from VK social network in this round as well! Namely, among participants solved five or more problems in second division, or two or more problems in first division, five are to be selected randomly. They will receive championship souvenirs. There is no country nor language restriction, everyone can win a prize. One don't have to have participated in VK Cup to receive the prize. Exact selection algorithm will be announced before the start of the round.

Good luck!

Congratulations to the winners!

Div. 1:

1. Syloviaely
2. jqdai0815
3. Petr
4. anta
5. matthew99

Div. 2:

1. ccz181078
2. repeating
3. ioyeoa
4. ReaLNero
5. beet

The analysis is here.

The problems correspond to problems of VK Cup 2017 - Finals as follows:

• Problem 830C - Bamboo Partition — is problem 823C - Bamboo Partition, author is me;
• Problem 830D - Singer House — is problem 823E - Singer House, authors are send_nodes and me;
• Problem 830E - Perpetual Motion Machine — is problem 823F - Perpetual Motion Machine, authors are akvasha and ilya_the_lamer.

Congratulations to souvenir winners!

We invite you to participate in the boot camp that will be held at Yanka Kupala Grodno State University in collaboration with Moscow ACM ICPC Workshops from 15 to 25 August, 2017.

The cost of participation per single person is: 490 USD.

The cost features the curriculum, food and accommodation at the Grodno State University campus and trip schedule on days-off.

Grodno State University, being located almost in the center of Europe, is one of the centers for ACM ICPC coaching. Among the events hosted at GrSU are: bootcamps and open competitive programming championships.

Registrate here!

Recommended time of arrival: August 14, or 15 until 12:00am

Recommended time of departure: August 26, or 25 after 20:00 (8pm)

Look here for more information.