Hello, Codeforces!

Educational Codeforces Round 7 will take place on 10 February 2016 at 18:00 MSK for the first and second divisions. You can read about educational rounds here and here.

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The round will be unrated for all users and it will be held with extented ACM ICPC rules. You will have two hours to solve six problems. After that you will have one day to hack any solution you want. You will have access to copy any solution and test it locally.

If you have ideas for some problems or maybe already prepared problems that you can't use in rounds or official competitions, you can write to me.

</This paragraph was modified last time>

Thanks a lot to Aleksa Plavsic allllekssssa who suggested the problems D, E and Ivan Popovich NVAL for the problem F. Also thanks to Mohammad Nematollahi Deemo who suggested the problem that was highly simplified and will be under the letter C.

The round was prepared by me, Edvard Davtyan. Thanks a lot to MikeMirzayanov we invented the problems A, B and C together. Also thanks to Maria Belova Delinur for checking the English statements, Aleksa Plavsic allllekssssa and Ivan Popovich for testing the problems.

We tried to make the problems easy but interesting. I think that the problems is mathematized a little. I hope you will enjoy the problems!

Good luck and have fun!

P.S.: The Codeforces Educational Rounds was recognized by Snarknews as the best project in competitive programming in 2015 (the picture below is the prize).

UPD1: The first phase of the contest is ended. You can hack any other solution.

UPD2: The editorial is ready.

UPD3: The round is over, the results is final.

Hello, community!

Tomorrow Codeforces Round #342 is going to take place. It will share the problemset with Moscow Olympiads in Informatics for students of grades from 6 to 9. Though, grades from 6 to 9 in Russia usually match the ages from 12 to 15, I guarantee that everyone (even Div. 1 participants) will find some interesting problems to solve. Problems were selected for you by the Moscow jury team: Zlobober, meshanya, romanandreev, Helena Andreeva and me; and prepared by members of our scientific committee: wilwell, Sender, iskhakovt, thefacetakt and feldsherov.

Scoring distribution will be quite unusual: 750-750-1000-2000-3000.

UPD System testing is over. Here are the top 10:

1. _XuMuk_
2. pandamonium
3. latisel
4. zetamoo
5. yukariko
6. I_Love_Ximera
7. kittylover
8. shdut
9. harry.zhao
10. luke0201

Congratulation! Also, problems seemed to be too tough, we should have probably made Div. 1 round. Anyway, thanks for participating, I hope you enjoyed it and learned something new!

Thanks to romanandreev for nice analysis.

Hi, Sharif University of Technology is holding an international AI competition. You may read a short description about it below:

=========

Student Scientific Chapter of computer engineering department at Sharif University of Technology will hold the first international Sharif Artifical Intelligence Challenge on March 2nd and 3rd.

This competition will be held in two phases including an online and an on-site phase in which competitors will compete in teams of three in a game designed by our technical team.

The only pre-requisite to enter this competition is familiarity with programming using C++, Java or python. But obviously, knowledge of algorithmic thinking and artificial intelligence will be a great asset for any of the participating teams. The registration for online competition is free and open from february 1st through to february 8th available at http://aichallenge.sharif.edu .

After finishing the online phase which starts on February 9th and continues untill February 17th we will run submitted codes and teams with highest scores will make it to on-site competition. Winners of on-site competition are awarded. For further news and announcment please checkout our blog at http://aichallenge-en.blog.ir or follow @aichallenge on twitter and instagram.

THE COMPETITION IS FIERCE.

=========

UPDATE #1: On-line competition is open to everyone however to participate in the on-site contest you have to be a student. You may participate in the on-line competition with a team of at most three members however participating in the on-site contest requires a team with exactly three members.

Hi, Codeforces!

AIM Tech Codeforces Round will take place on February, 4 at 20:05 MSK.

The round is prepared by AIM Tech employees: Kostroma, riadwaw, yarrr, ArtDitel, ValenKof, bobrdobr, agul, gchebanov and zeliboba. Round will take place during Petrozavodsk Winter Camp, which is sponsored by our company.

We made our problems a little easier than at our last Round, but we promise they won’t be less interesting. Scoring system will be static. The final distribution of points will be announced right before the round, however you should note that this time difference in complexity between problems div1 C, D and E may be less than usual so our strong recommendation that you read them all first.

Thanks to Mike Mirzayanov(MikeMirzayanov) for brilliant platforms Polygon and Codeforces, problem coordinator Gleb Evstropov (GlebsHP) and Maria Belova (Delinur) for English translation.

Our company specialises in proprietary trading, the key concepts in our work are big data, low latency and high frequency. Our team mainly consists of graduates from the MSU Faculty of Mechanics and Mathematics and Moscow Institute of Physics and Technology (MIPT).

We wish you good luck and high frequency rating!

P.S. For all participants of PTZ gathering we are glad to announce evening buffet that will take place at Paulaner Brauhaus and will start Februrary, 5 at 7:30 pm

Scoring

div2: 500 — 1000 — 1500 — 2000 — 3000

div1: 500 — 1000 — 1750 — 2000 — 2250

Editorial

P.P.S. Author solution of div2A had precision error 5e-7, so we decided to rejudge this problem.

Hello Codeforces!

I invite all of you to participate in a special Codeforces round. It will take place on 29 Jan, 17:05 UTC. It will not be a usual round. Thanks to Wunder Fund, the best participants will win prizes and souvenirs. Here are some words from Wunder Fund:

Our company is situated in the center of Moscow. We are engaged in high-frequency trading — developing high-performance systems and algorithms for automated trading in financial markets. In this area algorithms and data structures (that you love to invent and implement) are vital. Our systems should process transactions in milliseconds! High-frequency trading is a continuous competition of the best programmers and mathematicians around the world. By joining us, you will become a part of this exciting challenge.

We offer interesting and challenging tasks for the development of low latency for enthusiastic researchers and programmers. Flexible and no bureaucracy, decisions are taken quickly and implemented. We are a small team, so you will immediately become a significant part of it. Understand the economics and finance is not required, but the algorithms and data structures is what we need.

Are Russian speaking and ready to live in Moscow? Join us! Visit our website for more information.

We will be happy to give participants prizes and gifts:

• 1 place — PlayStation 4
• 2 place — Xbox One
• 3-5 places — Sega MegaDrive 16bit with games
• 1-50 places — Wunder Fund T-Shirts!
• 51-500 places — 50 T-Shirts to random participants!

I want to thank the following people for helping me with this round:

• GlebsHP for his help in reviewing problems and assistance in preparation for the round.
• LiChenKoh, AlexFetisov, and winger for testing problems.
• Delinur for translations.
• MikeMirzayanov for Codeforces and Polygon systems.
• and of course Wunder Fund for sponsoring the round.

I hope to see you all at the round. Good luck and have fun! :)

If you'd like some practice before the round, you can look over some of my past rounds that I've written (links here: A B C). I will try to give you all some more interesting problems to solve.

UPD1: The round will be 2 hours and 7 problems. Unfortunately, there are some time conflicts, so we are unable to extend the duration of the round. The score distribution will be 500-1000-1500-1750-2500-2750-3500. Note that some problems that we thought are harder may actually be easier for you, so I encourage you to read all problems.

UPD2: The editorial is published. Congratulations to the winners

1. Egor
2. Petr
3. Um_nik
4. RomaWhite
5. Sampson

Hello.

Now Codeforces will be more convenient to browse from mobile platforms. For the majority of them mobile view is available now. The menu goes to the left panel and sidebar — to the right. Both panels are available either on special icon at the top of the page, or by swipe left/right. You can hide them by touch in the main area of ​​the page, or by reverse swipe. In the mobile view fonts are enlarged, so on most screens it is possible to read the website without zoom.

So, for example, how the sidebar appears on my phone:

You can switch off mobile view (or to switch off) by clicking the special link in the bottom of any page.

P.S. In old browsers, and generally on a non-webkit it may work incorrectly. Not sure it is easy to fix :-(

Hi!

Tomorrow, on 23rd of January at 18:35 MSK Codeforces Round #340 (Div. 2) will take place. It's my first round, hope you enjoy the problems.

Thanks to GlebsHP for his help in preparing the problems, Delinur for translations of statements and MikeMirzayanov for Codeforces and Polygon.

Good luck!

UPD Scoring 500-1000-1250-1750-2750

UPD Editorial

UPD Congrats to winners!

Div. 2

1. AReesha

2. kpw29

3. I_love_Varechka

4. zhaoxinyi

5. thatday

Div. 1

1. anta

2. dreamoon_love_AA

3. uwi

4. Um_nik

5. I_love_Tanya_Romanova

Warning! The dates of the Winter Computer Camp have shifted one day ahead!

Update: due to technical difficulties, English speaking participants couldn't participate in the fourth selection round. Due to this, the Organizing Committee decided to carry out another selection round on 14 February at 15:00 Moscow Time. Everyone is invited to participate in this round, but preference will be given to foreign participants preeminently.

From 25 February to 5 March 2016, the Moscow Insitute for Physics and Technology will host the seventh Winter Computer Camp 2016 (WCC-2016) in the city of Dolgoprudny. Students of upper grades are welcome to participate.

The program of the camp includes::

• Daily studying contests: preparation to the finals of the Open Olympiad, finals of national programming Olympiads.

• Olympiads in programming and mathematics.

• Lectures by workers of base organizations of FIHT about actual tasks in the IT Industry.

• Lectures by professional scientists on combinatorial mathematics.

• Sports and intellectual games.

How to get to the school:

1. Fill in the registration form.
2. Participate in the online selection rounds for the camp. Pay attention that the selection is conducted thoroughly in compliance with the results of the selection rounds.

Online selection rounds*:

• 27.12.2015 15:00 (UTC+03) — first round,

• 17.01.2016 15:00 (UTC+03) — second round,

• 24.01.2016 15:00 (UTC+03) — third round,

• 07.02.2016 10:00 (UTC+03) — fourth round

**the dates and time of the rounds can change, follow the information on [our website].(http://it-edu.mipt.ru/en/zksh2016).

Cost of participation:

• Free participation is guaranteed to the winners and prizers of the final stage of the All-Russian Olympiad for School Students (or CIS Olympiads) in Informatics and Mathematics.

• 9900 for winners and awardees of the ALl-Russian Team Olympiad for School Students in Programming and the Open Olympiad for School Students in Programming.

• 15900 rubles for participants of the final stage of national Olympiads for school students in informatics and mathematics

• 28900 rubles for other participants.

For any occuring questions, leave messages on the organizing committee email: zksh-team@phystech.edu

The head of programming committee of Winter Computer Camp 2016 is Endagorion.

The Winter Computer Camp is traditionally unique for its line-up of participants: Dolgoprudny hosts large numbers of capable students who already have achievements in All-Russian and National Olympiads of different countries. Preparation of contests is performed by young teachers, professors and students — prize-winners of All-Russian Olympiads for School Students and ACM ICPC student tournaments. Therefore, participation in the WCC-2016 serves as a "final rehearsal" before the Finals of the Open Olympiad and the All-Russian Olympiad in Informatics.

Hello, Codeforces!

Educational Codeforces Round 6 will take place on 21 January 2016 at 18:00 MSK for the first and second divisions. You can read about educational rounds here and here.

<Your Ad Could Be Here>

The round will be unrated for all users and it will be held with extented ACM ICPC rules. You will have two hours to solve six problems. After that you will have one day to hack any solution you want. You will have access to copy any solution and test it locally.

If you have ideas for some problems or maybe already prepared problems that you can't use in rounds or official competitions, you can write to me.

</Your Ad Could Be Here>

Thanks a lot to Aleksa Plavsic allllekssssa who suggested several problems, two of them you will see on the round (the problems D and F). Also thanks to Bayram Berdiyev bayram, Allanur Shiriyev Allanur, Bekmyrat Atayev Bekmyrat.A. They are together suggested five problems, two of them you will see on the round (the problems B and E).

As usual the round was prepared by me, Edvard Davtyan. Thanks a lot to MikeMirzayanov we invented the problems A and C together. Also thanks to Maria Belova Delinur who will check English statements and Aleksa Plavsic allllekssssa who help me with problem testing and have constantly been in touch.

The first problem is pretty simple, so I'm waiting fast accepteds from you. The last problem is pretty difficult, so respect to all particiants who will solve it. I hope you will enjoy the problems!

Good luck and have fun!

UPD 1: I forgot to thank all other users who already sent me the ideas for the problems. I'll try to give that problems to the next rounds.

UPD 2: The main part of the contest is finished. The phase of hacks is started.

UPD 3: The editorial is ready.

UPD 4: The round is over, the results is final.

Teams advancing to 2016 WF Phuket in Asia have been announced recently. This announcement is undisputedly tantamount to a death sentence for me. I am the one waiting anxiously, refresh Dr. Hwang's blog everyday. But it seems that for years, our training was meaningless.

I think many of us dedicate our passion to programming contests because we see them transparent, fair and without any corruption. And I also believe that as contestants, what we should do is only focus on the practice. And I thought those political business should never come to bother me one day. But sadly, it is my team who is going to become one of the sacrifices of a succession of the dissension.

What happened so far

The quarrel between the Asia director and the local community is a long story to tell. But it has never been as serious as it was in the past season. Now reflecting on this, I know on the surface everything is going okay, but I still feel something wrong. The number of slots is decreasing, as well as the power of those multifarious bonus are rising. So the feeling of the unfairness multiplied. According to this article, before the last day, you do not know the exact X or Y in his algorithm. That means, you can always put any number to these parameters after the contest. And the way he decided to put in those variables, which was quite arbitrary and dictatorial. I am afraid those parameters were used to suppress opponents and those who are close to Dr. Hwang will be easy to pass. Now can it be right, to reject a team on the relationship between the authority? But it is exactly what we do, and now it is almost a open secret for us. If you guys have any opposition, you are directly set yourself to the hard mode. In quicksort, there is a strategy called “killer adversary”, I think that is exactly our situation. In fact, last year in China, the contest divided into 2 events, one called ICPC and another is called CCPC. The CCPC event is simultaneous with Changchun site. And some of the school last year was united to refuse to take part in Changchun Site in order to against the overladen bonus, according to the board, we could see there are lots of strong teams seems didn’t come and take part in the Changchun site. But despite of this, Changchun site still get 1 more slot than other sites, and some site has 3 slots while some site is only 1 slot barely. Is that fair? I don’t think so. Last year, I thought staying in the top 6 could have a chance to enter final… This year, I thought staying in the top 2 must have a chance to enter final. As far as I know, there is no team in our region in history which get 2nd place but cannot go to final. And the logic is the same as what he has done on the Chennai flood. Initially a rule was brought out to reduce the number of slots from Chennai to 1. It was later decided to award an extra slot to Chennai. But it turned out, this extra slot was actually the bonus slot that was going to be given to Amritapuri (as it had proposed to host the world finals in future, smell some sense of Stockholm syndrome?). The net effect is, the number of teams from India is reduced due to postponement rule announced so hastily after the Chennai regional was postponed. This awarding of the extra slot to Chennai is just a sleight of hand designed to look like it is fair.

My wish

Well, don’t get me wrong. I am not against the rule this year, I am against the way the rule has been made. The problem with this system, is that it’s this sort of long, slow expansion in personal power. If you don't make a sound this time, things may become more and more dangerous in the future. One of my spiritual idol Aaron Swartz once argued that it was sometimes necessary to break the rules that required obedience to the system in order to avoid systemic evil. So, at my point of view, at least all officials concerned should be consulted. There should be some discussion before taking any decision. The voting should be transparent. The slot calculation is needlessly complicated and could be much simplified. There could be bonus slots but shouldn’t affect the acknowledged game rules. There should be no parameters remain to be determined after the contest. I know in the early day in the ICPC history, Dr. Hwang had done great contribution to bring this event for us. But as times alter, today, the power is overwhelming, and he is stand on the opposite of the sport spirit, the way in which Dr. Hwang makes decision should be questioned. What he has done this time is just to make an example out of us, to use this case for deterrence. So that next time we are submitted to his power. And if we could not do something that take a fair environment back, the reputation of the contest in the sub-region will be badly influenced. Do we really willing to see there are 5 CCPC together with 5 ICPC in the coming season? Do we really need this privilege to keep the health and vitality? I am afraid our students will be seriously exhausted on this issue and the community will appear to diverge further.

Update

Thanks everyone!

Dr. Hwang has just replied to me that he will try after one week for an additional participation slot for Asia. But still said nothing about the X+Y scheme. Looking for the further reaction. The chance is slim. But no matter what outcome will be, I have already felt the warmth of the community!