By cgy4ever5 days ago, In English,

Do you want to win a T-shirt? Do you want to learn how to design tasks for programming contest? Do you want to solve 7 tasks in 2.5 hours?

So Codeforces Round #270 is right for you. It was designed by me in California, Assembled in polygon (so Thank you MikeMirzayanov for the system and Gerald for organize and testing), will start on regular time this Sunday, don't miss it!

The organizers of Marathon24 decided to present gifts to the best finishers of the round! Best 25 participants will get Marathon24 tshirts! Thanks!

It is just an image to attract your attention. Real tshirts will be designed specially for Marathon24!

There are some articles introduced how to become a problem setter, like Problemsetter's Memoir and Way of problemsetter, but they focus on the process of contest preparation or high level thoughts. You might still don't know how to begin to write a contest: because you need to come up with ideas about problems in the first place.

In the last 3 years, I've designed lots of tasks, for example, there are 2 Codeforces Round by me (#190 and #228), and there are exactly 100 tasks designed by me on Topcoder. So I want to write a tutorial to share some specific ways to come up with new tasks.. Oh, wait, how about create a contest and write the tutorial in problem statement? So I get this idea: in each problem I will introduce a specific way of design, and I'll tell you how did I use this way to come up with a new task, and you need to solve that new task!

And this round will be a bit special: all contestants from Div1 and Div2 will compete in one contest, and it will contain all 7 problems! The duration is extended from 2 hours to 2.5 hours.

In the last, I'll do some self-introduction like marat.snowbear did in the announcement of last round. I'm Gaoyuan Chen from China, I lived in Beijing for 23 years till this August, and then I went to University of Southern California in Los Angeles to learn Game Design and Game Development. As a game designer, I'll try to make my round interesting and competitive. (And of course, there will be a problem about a popular game!) And I start to use Facebook after moved to US, so if you want to know more about me or want to chat with me, visit my facebook page:

More information like score distribution (so maybe we will have 3500p for last task!) will be announced later.

Good luck and have fun!

Update1 : score distribution: 500 — 1000 — 1500 — 2000 — 3000 — 3000 — 3500

Update2 : Contest ended. Thanks for participate! Any comment is welcome (you like the task? don't like it? it is too easy? too hard? Do you like the idea of Div1 and Div2 compete together? etc.).

Update3 : Editorial:

Update4 : System test finished! Top 5 (in fact Top 6 because of a tie):

  1. Petr

  2. Egor

  3. AlexDmitriev

  4. PavelKunyavskiy

  5. Jacob and rowdark

Update5 : Thank all of your support! I found I'm on the Top contributors list now. :)

Update6 : Statistics by DmitriyH:

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Announcement of Codeforces Round #270
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By marat.snowbear7 days ago, In English,

Hello Codeforces community! I'm happy to invite you to participate in Codeforces Round #269 for Division 2 which will be held this Friday, September 26th. As usual first division coders are invited to participate unofficially, I would appreciate a lot if they will join.

All problems are mine, so if you won't like them... well, you know whom to blame for those. I did my best in order not to disappoint you.

Since this is my first round, let me introduce myself. I'm 27, have around 7 years of programming experience and was never into ACM/ICPC and stuff like that before, learned words like "dynamic programming" couple of years ago from the algorithms course on Coursera and a bit later found this site. I'm from Saint Petersburg, Russia, was born and lived here until I became 24. Then I got married and me and my wife decided to go live somewhere else and we moved to Kyiv, Ukraine, and we love that city a lot and we will return there some day, hopefully soon.

I hope you will find my problem set interesting and varied. Meanwhile let me get you prepared for the round and introduce you the guys you will help to. So the heroes of my round are three animals from Saint Petersburg and Kyiv zoos. Those are Menshikov and Uslada ("Uslada" means Delight in Russian) — polar bears, symbols of Saint Petersburg zoo. These are my favourite animals of that zoo, they can do a moonwalk dance. Their third friend would be Khoras — an elephant from the Kyiv zoo, not sure what kind of dances he likes but he was very friendly last time we've been there. I was always fond of polar bears and elephants so now I have a round with them! Hope you will remember their names, in problem statements I call them by name and by animal type interchangeably. They want the friendship to exist between their countries and they have some minor problems you can help them with.

Traditional and untraditional regards for this round go to:

  • MikeMirzayanov and the entire team of Codeforces for the site,

  • Gerald for his help with the problems,

  • Maria Belova aka Delinur for the translation of the statements,

  • last but definitely not least, my wife Tanya for her infinite support in everything I do. This round wouldn't be here without her.

Wikipedia asked me to remind you that the day we'll have the round (at least in Russian tome zone and time zones close to it) is 269th day of the year, matches the round number perfectly thanks to Gerald's scheduling skill.

If you read up (down?) to here and I still have your attention then let me know the secret every non-red coder wants to know — in order to become red you need to solve at least 1513 problems on this site. That's a personal experience, trust me.

Another thing I'd like to mention here: gojira was cheating! In his round announcement he mentioned that he's taking the 'eldest problem setter' title from Sammarize but he didn't mention his age, so I can't tell whether this title should be mine or not. gojira, please let us know ASAP!

Will see you on the round and I will appreciate a feedback (both positive and negative) a lot!

P.S.: as usual the scoring will be announced closer to the start time, hopefully my memory won't fail and I will update this blog post then.

upd 0: small update for the English version. In English statements the names of the characters will be Menshykov, Uslada and Horace, don't get surprised :-)

upd 1: scoring will be a bit different from normal today: 500, 1000, 2000, 2000, 2500

Thanks to everybody who was with us today, hope you enjoyed it! My congratulations to the winners. worse didn't take part in today's contest so the fight was tough on both sides of the table. While Menshykov and Uslada are updating the ratings, Horace is finishing the editorial, he's promising it will be ready a bit later today.

I understood and noted some mistakes of mine in this contest, but please let me know if you have anything to tell about it. I like how it's started, thanks for beating the 5K record, that's awesome.

Unfortunately nobody solved E, though hos.lyric was very close to it. His solution failed on the second to last test, which I didn't consider to be a max test. I consider this to be my mistake that I underestimated the problem, otherwise I would leave it for some next contest.

Best regards,
Will see you at some next round,

Round stats from DmitriyH

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By MikeMirzayanov6 days ago, translation, In English,

Welcome to 2014-2015 CT S02E03: Codeforces Trainings Season 2 Episode 3. The training duration is 4.30 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!

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By monsoon8 days ago, In English,

Hello everyone!

Once again we invite you to participate in the 24-hour team programming contest Asseco Programming Marathon24 Gdynia 2014. Powered by CodiLime. The first edition in 2013 was quite a success: 243 teams of three from over 20 different countries were registered for the contest and 30 teams from 8 countries were qualified for the finals in Gdynia.

In the contest teams of three can participate. There is no limit concerning the age or education of contestants. Also there is no limit in equipment, programming languages or materials you can use during the contest.

The contest consists of two stages. You can check out problems from the first edition to familiarize yourself with the format. This year's tasks will also be prepared (among others) by Tomasz Idziaszek monsoon and Wojtek Nadara Swistakk.

The first stage are qualifications, which will start on 11th October 2014 at 9:00 CEST and will last for 5 hours. There will be 5 algorithmic problems, to which 10 test cases will be provided. You only submit outputs to the tests and you get immediate feedback on your score.

No more than 30 teams with the highest scores will qualify for finals. They will take place in Pomeranian Science and Technology Park in the city of Gdynia in Poland. Finals will begin on 29th November 2014 and will last for 24 hours. There will be 3 problems, which will require you to write a program communicating with the contest server through the TCP/IP protocol.

For three teams with the highest scores in finals there are prizes amounting to over 30 000 PLN in cash. For more information visit our site: The registration closes on 9th October 2014.

Update: Also be sure to take part in Codeforces Round #270, for the top 25 participants of this round will get Marathon24 T-shirts!

Good luck and have fun!

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By dalex2 weeks ago, translation, In English,
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By 233333333333313 days ago, In English,

Hello everyone! Codeforces Round #268 is coming soon! We invite you to participate in this round. It will be held on September 20th at 17:00 MSK.

Problems have been prepared by me. Thanks xyz111 and dhh1995 for giving me the idea of some problems. Thanks vfleaking, foreseeable, xiaodao, ruchiose and xllend3 for testing.

I also want to thank Gerald for helping to prepare this round, Delinur for translating the statements, and also MikeMirzayanov for Codeforces and Polygon.

It is my first round on Codeforces. Hope you will enjoy this round.

You'll help a boy named Little X in this round. Good luck and have fun :)


Round has finished. Thanks for participating.

Congratulations to the winners.

Div. 1

  1. PavelKunyavskiy
  2. Kostroma
  3. HellKitsune
  4. Baz93
  5. DemiGuo

Div. 2

  1. manman
  2. topcodecheforces
  3. mhy12345
  4. sk_aswd
  5. z.last

Congratulations to ecnerwal, the only participant to solve the problem D!

Unfortunately, no one has solved the problem E in both divisions.

Editorial for the round will be added tomorrow.


Editorial is here.

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By KrK2 weeks ago, In English,

Hello, guys!

I invite you to take part in the last year's competition which took place in Kaunas University of Technology and had participants from three different Universities in Lithuania.

The best participant was selected to KTU #1 (the 30th place in the last year's ACM finals) and other top KTU participants were selected to KTU #2 and KTU #3 teams.

Moreover, some of the hardest tasks were used in the preparation for IOI competition.

The contest is scheduled on Saturday, Sep 20, 2014, at 12:00 PM.

As the contest has three stars of complexity, it may be very interesting for Div. 2 participants, but I don't recommend it for Div. 1 participants and those who already participated in the contest.

All kinds of feedback are gladly accepted, as this contest is also a dress rehearsal for this year's KTU qualification round which is prepared with Polygon and will be made public for all Codeforces participants.

Enjoy the contest!

Solutions written by the authors of the problems:

All problems have been fixed

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Statements of K1 training
Tags gym, ktu
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By MikeMirzayanov2 weeks ago, translation, In English,

Welcome to 2014-2015 CT S02E02: Codeforces Trainings Season 2 Episode 2. The training duration is 4.30 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!

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By K0T2 weeks ago, translation, In English,

Hi everyone!

Codeforces Round #267 will take place on September 18th at 19:30 MSK My name is Yura and this is my first Codefocres round and I hope not the last.

I'd like to thank Fedor Korobeinikov (fk2012) and Alex Vistyazh (netman) for helping me to test all the tasks and prepare this round. Also, special thanks Gerald for helping me to prepare the tasks, Delinur for translation of all problem statements into English and MikeMirzayanov for Codefocres and Polygon.

I hope that everyone will find the problem for himself, and plunge into the student's life.

Good luck! =)

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