Hi!

Time brings to you next Codeforces round, this time it is with number 129. It will take place in 11.07.2012 at 19:30 (Moscow time). This time the problems are authored by me, Vitaliy Herasymiv. Long time ago I was the author of 4 Codeforces rounds, they were about lucky numbers. But, unfortunately, nothing is constant, so this time there will be no problems about lucky numbers.

A lot of help in preparing of the problems was from Gerald Agapov (Gerald), Alexander Kouprin (Alex_KPR), Vitaly Aksenov (Aksenov239), The problems were translated to English by Maria Belova (Delinur). Thanks to all of them.

I hope you will like this all.

Good Luck!

Div1:

Thanks all! The results are the following:

1. tourist (now tourist become first Codeforces target, congratulations to him)
2. winger
3. RAVEman
4. rng_58
5. RAD
6. bmerry
7. Shik

Div2:

1. xiaoshua2
2. ahm.kam_92
3. HanzhongBall_Quanling
4. daidailanlan

You can read editorials here.

Hi everybody!

The VK Cup 2012 programming championship finals is going to take place very soon. The organizing committee and jury are working around the clock to set up the event that the participants will like.

Let us remind you that the finals will take place from July, 13 to July, 16. We will choose the best 50 participants by the results of VK Cup 2012 Round 3. As soon as we are absolutely sure about who can come to the finals, we will publish the list of the finalists.

We’d like to share some information from the organizing committee headquarters. The finals’ participants will be accommodated in the beautiful Kempinski hotel in the centre of St. Petersburg, on the bank of the Moika. The hotel is located within a walking distance from the Vkontakte office, so there won’t be any exhausting buses and coming across the city’s traffic jams! Please note the roof restaurant with the view on the Palace Square when you take a look at the photos of the hotel.

There is no exact timetable yet, something depends on the time when the participants will arrive and the complexity of the problems (that’s right, the final round may not have the usual timing). The general plan is as follows:

• July, 13: Checking in, having dinner, meeting each other and having fun.
• July, 14: Most of the day will be dedicated to an unofficial entertaining event called Code Game Challenge (special for VK Cup 2012). Also a short testing tour is planned on that day. In the evening the great dinner will be topped with Code Game Challenge Show – watching the strategy tournament on a large screen.
• July, 15: The main day of the competitions (good luck!). In the evening we’ll reward the winners and celebrate all finalists (I am sure that everyone will be pleased :));
• July, 16: Going home.

Vkontakte and Codeforces are very glad to see the students’ interest in VK Cup 2012. Despite us inviting only young coders to the championship (the age limit should not exceed 23 years), nearly 6000 participants registered there. They geographically cover practically all countries of the world! We are very glad to see that almost all coders who advanced to the finals could make it to St. Petersburg. The winners will get worthy awards, and at this point we are happy to announce that the championship prize fund has been increased! You’ve got an aim to fight for and do your best to win!

• 1st place — $20000
• 2nd place — $10000
• 3rd place — $5000
• 4-5th place — $2000;
• 6-10th place — $1000.

Easy journey to the finalists,
The VK Cup 2012 jury and organizing committee.

Questions and Answers

• What will be the rules of the Final Round? The round will be held by the rules of Codeforces, it will be 2 or 2.5 hours long. The dynamic problems' scoring is likely to be used.
• Will we use the PCs that you will give us, or our own PCs? The participants will use special workstations prepared by the VK Cup Team. It is not allowed to use one's own laptops. You may bring a USB-keyboard, but it should not have superior features.
• What operation system will be used? We hope to give the oppotunity to boot Ubuntu 12.04 or Windows at the participant's choice. We are working on it now. We will install a wide list of free software on both OS.
• Is it possible to use a prewritten code? Basically no, it is only allowed to use the code written on the competition. But you may use the code written on the practice session or on the CodeGame coding phase.

Saint-Petersburg photos

Hello, friends!

A few hours later you're lucky to participate in this remarkable Codeforces Round #2⁷ for Div. 2¹ participants, but traditionally the others can take part out of the competition.

It has been prepared by a small band of authors: me (NALP), Igor Kudryashov (Igor_Kudryashov), and Pavel Kholkin (HolkinPV). There were Gerald Agapov (Gerald), Maria Belova (Delinur) and Mike Mirzayanov (MikeMirzayanov) with us as always.

It’s well-known that you can participate in this Round into competition only today! There won’t be another Codeforces Round #2⁷!

Traditionally I wish good luck, accepted solutions and successful hacking attempts for you!

UPD: Points are standard: 500, 1000, 1500, 2000, 2500.

UPD: Round is over, thanks to all! We hope you have got a fun. Don't forget, system testing will be soon.

Hello everyone!

As many of you already know, today is the day for Codeforces Round #127 missing which is really undesirable ;)

Original problems for you were created by tourist and Romka. We tried to emphasize the ideological component of the problems, thus we hope that you'll spend more time thinking than coding. Special thanks for helping in setting the contest go to Codeforces coordinator Gerald. We also thank Delinur for translating the problem statements and Alex_KPR for reviewing them.

We hope that this round won't be just a regular Codeforces round for you, but will bring you new experience and new knowledge. For the authors all problems are equally easy, yet we tried to arrange them in decreasing order of simplicity :)

Problems' point values in Division 1 are 1000-1000-1500-2000-2500. Problems' point values in Division 2 are 500-1000-2000-2000-2500.

Wish you success!

UPD: The contest is over, thanks all for participating. We hope you enjoyed it :)

In Division 1 rng_58 was a clear winner, solving all 5 problems in an hour and a half! No one else managed to solve all problems in two hours.

The winners in Division 1 are (full results):

1. rng_58

2. peter50216

3. liympanda

4. White_Bear

5. havaliza

In Division 2 every problem was solved by somebody, but nobody managed to solve all problems. The battle was very tough and the gaps were very small.

The winners in Division 2 are (full results):

1. Leewings

2. snow_lotus

3. 72VanVector_SevNTU

Congratulations to the winners!

UPD2: The editorial is available now.

Good afternoon, friends)

We introduce you Codeforces Round #126 (Div. 2). Please note, Codeforces Round #126 (Div. 2) will be only today and only today you will have unique opportunity to raise your rating in this competition (certainly, you will be able to solve problems virtually after round, but this doesn't change your rating). Also round will be unrated for participants from first division.

This round was prepared by students of Saratov State University: Nicolay Kuznetsov (NALP), Pavel Kholkin (HolkinPV), Igor Kudryashov (Igor_Kudryashov) and Gerald Agapov (Gerald). Also we thank creator of Codeforces Michael Mirzayanov (MikeMirzayanov) for amazing system, member of staff of Codeforces Mary Belova (Delinur) for great translation and Alexander Kuprin (Alex_KPR) for help in preparation of this round.

Note, today it is decided to use dynamic scoring system (Learn more about dynamic problem scoring).

Also problems will be placed in random order, it means they aren't sorted in increasing order of difficulty.

More right ideas and fine solutions to you.

UPD. Competition is over. Thanks for all who participated. We hope you enjoyed the participation, and round not passed in vain. Editorial will be posted soon. Congratulations to the winners:

1. Andreos

2. jma127

3. iensen

4. Spider-man

5. MrPapaya

Hello everyone!

There is yet another Codeforces round. Now it is the 5³-th one.
The round will run for both divisions by classic rules of Codeforces format.

Points are standard: 500-1000-1500-2000-2500.

Round was prepared by Ripatti , Alex_KPR , Gerald , Aksenov239 , RAD , Delinur .

Good luck!

UPD. Round is ended.
Winners of div1:
1. Petr
2. tourist
3. SergeyRogulenko
4. bmerry
5. UESTC_Nocturne

Winners of div2:
1. gflegar
2. mylyanyk.ivan
3. arbesfeld

Petr is only who solved all 5 problems in the first division. No one solved all 5 problems in the second division.

UPD. Editorial.

Hi all!

Today, June 12, when Russia celebrates Day of itself, Euro 2012 second round starts and I_love_natalia has a birthday, we present you Codeforces Round #124.

Contest was prepared by team Samara SAU Teddy Bears (craus, dalex, Hohol) and I_love_natalia. Also thanks to Alex_KPR and Codeforces team (Gerald, Delinur, MikeMirzayanov). We think that contest is very easy, and your task will be prove of refute this assertion :)

Scoring system is dynamic (Learn more about dynamic problem scoring).
Authors think that problems are sorted by difficulty in non-descending order.

Accepted solutions and successful hacks to you!

UPD. Contest is over, congratulations to the winners!

Div-1 (full results):

1. tourist — the only one who solved all problems!
   
2. RAVEman
   
3. aropan
   

Div-2 (full results):

1. bmerry
   
2. littlefriend
   
3. gstsclq
   

UPD 2. Tutorial is available.

A couple of days ago I wondered how many authors (except for me) write problems about programming languages. I was hoping to be not alone in my passion to this topic; but the reality exceeded all expectations. Of course, problems which feature programming languages are much scarcer than ones about computers, processors, microchips, parallel computing, databases and other IT things, but still much more frequent than ones about, say, dragons :-)

1. TopCoder

The early years of TopCoder presented the participants with several programming-languages-featuring problems.

Welcome, friends)

We are glad to introduce you regular Codeforces round #123 for Div.2 participants. Everyone can traditionally participate in it.

Problems are prepared by command of authors: Ivan Fefer (Fefer_Ivan), Igor Kudryashov (Igor_Kudryashov), Pavel Kholkin (HolkinPV) and Gerald Agapov (Gerald). Also thanks to Pavel Kunyavskiy (PavelKunyavskiy) and Alexander Kouprin (Alex_KPR) for their help. And traditionally thanks to Michael Mirzayanov (MikeMirzayanov) for Codeforces system and Mary Belova (Delinur) for translating problems.

Score distribution is standard: 500, 1000, 1500, 2000, 2500.

We wish you success and high rating!

Congratulations to winners:

1. bmerry
2. adrian.jaskolka
3. cheshire_cat
4. alexej
5. psw

UPD: the tutorial is here

The upcoming contest is brought to you by me. My name is Arthur, I'm a student of Chelyabinsk lyceum 31.

I am glad to thank Gerald for contest preparation management, Delinur for translation of statements, MikeMirzayanov for a really excellent system, dolphinigle for test-solving, proof-reading and much valuable advice, fdoer, grey_wind, Skird and alger95 for help in problem development.

There is nothing more to say yet. As you can see, contest will be held in two divisions separately. The scoring system will be standard (not dynamic), but scores for tasks may be unusual (see update of this post).

There won't be volume stories. I hope you will like the contest and its problemset and everything will be OK.

UPD: Scores for tasks:

Division 1: 500-1000-2000-2000-2500

Division 2: 500-1000-1500-2000-3000

UPD2:

Congrats to winners =)

Div1:

1. Petr
2. tourist
3. yeputons
4. peter50216
5. aram90

Div2:

1. lucien
2. tomasz.kociumaka
3. sjynoi

UPD3 some part of English editoral posted. You will find the remaining part of the editorial later

UPD4 English editoral was completed.