Hello Codeforces!

I am pleased to announce a long term partnership with Harbour.Space University and Codeforces.

Harbour.Space is supporting the return of a new series of educational rounds on Codeforces!

They will take place with the regularity of ~2 times per month with the first round on 14:35 UTC, 27th of March, 2017.

Education Rounds Rules:

• Scholarships to study Data Science, Computer Science and Cybersecurity in Barcelona for best performing participants, courtesy of Harbour.Space University (more details later!);
• Classic Duration: 1.5 — 2.5 hours;
• The goal is rather to practice and to educate, than to compete;
• Not only problems, but also exercises can be used;
• Useful, even well-known ideas can be reused in order to introduce them to a wide range of participants;
• Unrated (perhaps only for now);
• We will conduct them in the ACM-ICPC mode;
• The results that are obtained after the end of the round, are preliminary;
• After the end of the round will be a 24-hour period of open hacks — any visitor of Codeforces may try to hack any complete solution to a problem of the last round (either from a contest, or from practice), the source code of hacking solution is available (you can copy the text and, for example, stress it);
• All successful hacks from the previous item will be added to the official test set and after as long as 24 hours after the end of the round retesting of all complete solutions will be made;
• Only after the final standings based on improved test data, the results are final;
• Our ability to process such problems are limited, so actually the test suites from the jury are expected to end up incomplete — we are looking forward to your hacks!

In February I had a new and wonderful experience of coaching top teams at the Barcelona ACM-ICPC Bootcamp hosted by Harbour.Space University. I was really impressed by the university, participating teams and fellow coaches from our community such as Endagorion, GlebsHP, Michael, Jacob and snarknews that were also there.

During the bootcamp it became clear to me that Harbour.Space University is a new type of university that’s reinventing the university experience. It is a modern, adaptable and flexible university that is doing amazing things in preparing talented students for careers in Computer Science, Data Science and Cyber Security.

All of their programs are developed in collaboration with the industry and are taught by the top professionals in the respective fields such as Viktor Kantor, Edith Elkind, Alexander Kulikov, Alex Dainiak, Sergey Nikolenko, Deepa Gupta and many others. I am delighted to be joining Harbour.Space fantastic faculty. Together we are developing a series of courses on competitive programming in addition to the bi-annual ACM ICPC Bootcamp that will be hosted by the university in Barcelona.

Hello Codeforces!

I'm pleased to announce the first championship hosted on the Codeforces platform. Welcome 8VC Venture Cup 2017!

8VC will be hosting a coding championship on Codeforces. The championship will begin on January 15 and take place in 2 rounds.

The contest will occur in two rounds:

• The Elimination Round is online and takes place on January 15, 17:05 (UTC). Elimination Round follows regular Codeforces rules and consists of 7-8 problems. For this round, the complexity of the problems will be comparable to a regular Codeforces round. There are no eligibility restrictions to participate in the round.
• The Final Round takes place on January 22, consists of 5-6 problems, and uses regular Codeforces rules. The complexity of the problems is higher than a regular Codeforces round. We will invite the top local finishers in Elimination Round to Woodside, CA to compete in the Final Round. In addition, we will invite the top 200 overall finishers to compete online.

Cool prizes are offered to winners and best participants.

PRIZES

• Overall 1st place — $2000
• Overall 2nd place — $1000
• Overall 3rd-5th places — $500 each
• Overall 1-50th place — t-shirts with 8VC and company logos
• Local Winner — Dinner with Joe Lonsdale (founder of Palantir, Addepar and 8VC) and other Silicon Valley technologists
• Local top finishers — Opportunity to meet with leadership from 8VC portfolio companies

ABOUT 8VC

8VC, which consists of Joe Lonsdale (co-founder of Palantir) and his core team from Formation | 8, is a Silicon Valley venture capital firm that invests in industry-transforming technology companies. The team's investment portfolio includes companies such as the selected companies below, and a host of other top technology platforms that leverage modern algorithms and data science to power their core business processes.

Hello, Codeforces!

At the request of Zlobober and other users I has implemented notifications on mentions. See the bell on the top of the page?

So far there is only the basic functionality and it is incomplete. But let's start with it for now.

Now notifications appear on mentions in comments only. For now it is impossible to disable it. We do not send anything on your email.

Let's test it together and understand how to move forward with this functionality.

From planned, proposed, discussed:

• Notifications on сhanges in the comments, on blog posts and their edits (if mentioned once, do not send more on edits)
• When you scroll, show a bell on the right side of the page, visually similar to the arrow ``scroll up'' on the left
• Possible we will restrict functionality to avoid abuse from inadequate users
• Special setting the profile
• Move other notifications to the new system (notifications on talks?)
• Shows a typical informational box in the right bottom on new notification

What else will be thinking?

In 2021, some details (including requirements for problem writers) were changed. Read the link for details.

Hello, Codeforces!

New year brings changes to the Codeforces team. As you probably know GlebsHP completed his work as the chief coordinator of Codeforces. Gleb, thanks a lot! You did an excellent job and coordinated a lot of interesting rounds. You're a professional, an interesting person, you have impeccable taste to problems, and you proved to be brilliant and talented writer. Thank you that you were with us! Hope to see your tasks on Codeforces many times again!

Nikolay KAN Kalinin came to Gleb's place. He is also an experienced participant, Nikolay has already held several rounds as a coordinator. KAN seriously engaged in programming contests since he was 12 years old. His major achievements: he won twice All-Russian School Team Olympiad; he won All-Russian School Olympiad (the 1st place!); he has two Gold medals in International Olympiad in Informatics (IOI 2013, 2014), bronze medal in the ACM-ICPC World Finals 2016 and he took the third place at the RCC 2016. This is the highest level! I am very pleased that Nikolay has joined the Codeforces team. I am confident we will succeed!

And here there is the first innovation of 2017 year. The idea to ​​organize work with proposals has swirled in my head for a long time. It turned out well: KAN visited Saratov to get acquainted with the whole Codeforces team and celebrate the New Year together. And we not only had a good time, but found some time to discuss details how we see our work with writers. Here's what happened.

Writers Requirements

All the functionality described below is only available for experienced contestants and writers of past rounds. There are requirements on the number of rated contests depending on your color (magic does not work here, sorry).

Please do not assume that the requirements are too strict. Our experience shows that it is hard to work with writers who are inexperienced as contestants . If you are a writer/jury member with experience in other competitions/events, please write KAN a private message about your wish to prepare a contest and describe your experience in this area. Be respectful to the coordinator decision, if it prompts you to achieve the general formal requirements prior to review your proposal.

Writers Reward

Preparation of the round is fascinating, but large and demanding work. We have the opportunity to reimburse the effort of the writers according to the following tariff:

An asterisk denotes a bonus, which is issued in case of work in time, without any issues

If a round is a part of a championship, there is an additional bonus, which is discussed separately.

I dream to raise reward to writers. I dream to see the most experienced, the most creative and interesting writers give our users the opportunity to participate in their rounds on Codeforces! Codeforces rounds attract record number of participants from around the world (the next frontier is 10000 registrations!), I personally offered a large number of problems — the chance to give an interest to participants is priceless.

Please send us your problems, spend contest proposals! We can make a platform, we can build a process, we can host championships. But we can't invent and prepare problems on each round.

How to propose a contest (можно читать всё!)

Those who meet the requirements will find the special link “propose a contest/problems” in the personal menu in the right sidebar. Click on it and you will have the opportunity to offer a contest, add problems to it. Read all instructions carefully. Carefully prepare and submit your proposal for a contest and for problems. I think that user interface is simple and intuitive.

Now, you can use only new system to submit proposals. If you have already received an answer from KAN for current proposal, you shouldn't transfer it to the new system. If the response has not been received yet and the proposal in actual, please, use the new system to send the proposal again.

The discussion of your ideas will be in comments mostly. Perhaps at a later stage it will be a possibility to communicate with the coordinator through any messenger.

Please be active, respond to coordinators' questions in time, make the proposed changes quickly. Remember that Codeforces coordinators are very experienced as participants and as reviewers . Their opinion is important, always balanced, and they have the highest priority in any decisions on the problems.

When the work goes to the preparation of problems in Polygon, the pre-read the examples of well-prepared problems, read all articles about using testlib. It is not difficult, but once you understand, you will be able to prepare high-quality problems for any Olympiad!

Conclusion

Later we come up with how to adapt the system for educational rounds (they come back!), for educational problems. With the new system we will get rid of lost proposals and can significantly automate and organize the process of working with them. I am sure that the system will be upgraded in the future and will become more flexible, more comfortable, more functional.

I hope that in 2017 we will host a lot of interesting rounds with your help. I hope you are waiting for them as well as I'm waiting!

MikeMirzayanov

Somehow it turns out that for me, each coming the New Year means more and more. This is an excellent opportunity to take stock, to breathe fresh air and to go through a kind of catharsis. This is a rare opportunity to be with the family, dress up in Santa Claus and just have fun.

Holidays give me a clear criterion that I do the right things. If during the holidays, I begin to think about it, to recall some deferred ideas, eager to implement something new. So I’m doing right things. My things. And now exactly the same as in several recent years: during New Year holidays I write code for Codeforces, trying new technology or simply I’m making minor changes in testlib. It is necessary to me: at this moment are no deadlines, do not press the obligation. Just now, at 3 am, I can not break away from being able to do something new. I would like to take a moment and realize that spun in my head the whole year.

I'm insanely happy to huge number (9144!) of registrations on Good Bye 2016. Your desire to grow, to learn new things, solve problems and invent, improve skills and compete, all this things give me strength and desire to develop the platform.

I wish you not to lose the fire in eyes, when you meet an interesting problem. I wish to continue to find pleasure in each contest or round. I wish to find, to solve more and more complicated and interesting problems. Victories and achievements! Wish you to solve all things which you didn’t solve in 2016!

Happy New Year!

But you, please read this post entirely. It is important to me. It draws the symbolic line to me and the whole Codeforces team. And, of course, below it is written about change handles gift and a colorful masquerade of ranks. Go!

Hello, Codeforces!

I want to test the system before Good Bye 2016, to be sure that everything works as expected.

I invite you to take part in Testing Round 13. It will start soon, on December, 29, 09:05:00 (UTC). It will be unofficial unrated round. The duration is 75 minutes.

Pretests are unusually weak to trigger more hack.

You may expect interactive problems. Hope for hacks for them.

Thank you,
MikeMirzayanov

UPD: Many thanks to all the participants. It seems the system works as expected. We are ready to host Good Bye 2016!

Hello, Codeforces.

Codeforces Round 389 (Div. 2) will start on December 25 (Sunday), 09:05 (UTC). It will be based on Technocup 2017 Elimination Round 3. So, if you are a Russian-speaking high-school student, please take part in the Technocup 2017.

Many thanks to KAN, fcspartakm, Endagorion, Kostroma and Golovanov399 Hope to extend the list soon because of testers. Also some problem ideas are mine.

I hope you will like problems. It will be 6 problems.

Wish you good luck and bugless code

UPD: The scoring is 500 - 1000 — 1500 — 2000 — 2500 — 2500

Hello all.

This coming February of 2017 will be a new experience for me: I'll be one of the coaches who will teach at the Barcelona ACM-ICPC Bootcamp hosted by Harbour.Space University. In addition, here are some well-known coaches from our community: Endagorion, GlebsHP, Michael, Jacob and snarknews. The camp will be hosted in collaboration with Moscow Workshops ACM ICPC by MIPT. The same proven effective studying techniques will be used at the Barcelona Bootcamp.

For me, it will be the first teaching experience outside of Russia as well as my first trip to Spain. I’ll do my best to coach you how to solve problems in an efficient fashion. Also, it will be an excellent chance to communicate about Codeforces personally with the real users.

Hello Barcelona Programming Bootcamp, in collaboration with Moscow Workshops ACM ICPC, is an opportunity for teams of different levels to prepare for successful participation in ACM ICPC. The Bootcamp will be split in two divisions:

• Division A. Designed to prepare students to excel and win medals in the next ACM-ICPC World Finals.
• Division B. Designed to help teams prepare for the next season of ACM ICPC Regionals and international competitions. This is an appropriate introduction for teams and students new to the world of ACM ICPC and competitive programming competitions in general. The Division B curriculum features thematic lectures and contests.

The participation fee is €1270 per person (cultural programme, accommodation and meals included). The location in Europe gives the effect of the rather high cost. Anyway, the event is non-profitable for these reasons: To prepare world-wide teams for ACM-ICPC and to scale Russian expertise of coaching on other countries.

The Bootcamp will start on February 6th and will last for 9 days to February 14th. If your team (or you individually) is interested to take part, please register before December 24th, 2016 by the link (discount 20% for registration in time):

Register
to Barcelona ACM-ICPC Bootcamp

You can ask any questions by email hello@harbour.space

Hope to meet you on the Bootcamp,
MikeMirzayanov

Good afternoon.

Sorry. Unfortunately, today (on Friday) we can't run the round 383 :-(

In short, this is because of technical reasons. For those interested in a more detailed description option.

On Thursday night I got sms. It was written that on server for DB backups free HDD space is less than 10%. This server stores three copies of the database over the last three days. It has 2TB drive and Codeforces database over 600GB now.

Since the next day I had planned to spend on the train on the way to NEERC, I decided to delete some redundant data from the DB. I estimate it will give several tens of gigabytes of free space.

I run query to remove redundant data and it was a mistake. I seems because of huge table to update (tens millions of rows) estimated time for the query to compete was at least several hours. As a result, I have killed this query, making KILL QUERY. But the database has continued to lag, I decided to restart it. Operation to shutdown the DB hanged for ~2 hours (I think it was rolling back the transaction), and the DB has stopped to respond and has become quite sad. As a result, I killed the DB process in the operating system and the database already refused to start without a recovery operation, which is also wasn't completed in a couple of hours. In short, I have struggled with this from 5 am to 9 am.

To make Codeforces live I reconfigured it to use database replica in the remote datacenter (in Mail.Ru). Before boarding the train, I started the process of transferring data from the replica back, but contrary to my expectations, this process has been very slow.

It is impossible to run the round using a remote reserve database server. Therefore, we have to move the round forward to Tuesday.

My apologies. I spent many hours struggling with technical issues and worked up to the last. However, it seems the bottleneck is in speed of data transmission over a network, in the speed to write on HDD and in the speed of innobackupex utility.

I hope that on Tuesday everything will go fine!

MikeMirzayanov

Good afternoon!

I've decided to share my thoughts on the round 382.

Of course, it turned upset not only to me, but also to the round coordinator GlebsHP.

In this round the main negative feedback were caused by two problems: 735D - Taxes and 735C - Tennis Championship.

Regarding 735D - Taxes. I do not share the criticism to this problem. In fact, to solve it would be nice to be familiar with Goldbach's Conjecture and better with Prime Number Theorem. These facts are medium-popular in the world of programming contests. Familiarity with them is useful, gives useful insight into primes. It is important: in this problem it was necessary to perform a simple, but nevertheless, additional step to find solution. It seems to me that it's okay to use problems that have a reduction to some popular and semi-popular topics. Otherwise, it is thrown away a huge number problems.

As a summary for this problem. I agree that the problem 735D - Taxes is not an example of the best problem. But it has a right to exist as one of the problems in a round. It can not take a role of any argument in favor of unrated round. I personally, would not include it in my contest. But the fact of the use of the Goldbach's conjecture (and more prime number theorem) is not a reason for me to convict and forbid a problem.

The situation with the problem 735C - Tennis Championship is much more complicated. It is necessary not to mix the two fundamentally different reasons for occurrence of same problems:

• Problems can be matched randomly, inadvertently. Of course, the coordinator and testers always have a critical look on the problem. At the stage of the contest preparation they immediately react if a problem is familiar to somebody. It is important to understand, that huge number of problems have been invented over the years of existence of sports programming. It is physically impossible to be familiar even with a large part of them. No matter how experienced the jury, sometimes, coincidences happen. Note that if the round is not a stage of a championship and its results do not affect prizes the main reasons for participation in it should be self-development and a desire to get a fan from the competition. None of these goals encourage search in Google.

• Deliberate coincidence or reuse of problems, it is a different story. And here it is what happened. This situation is totally unacceptable (educational rounds do not count), it is necessary to fight with it and to respond rapidly to incidents.

As soon as I examined about the incident, immediately called by phone the writer and discussed (and denounced) the situation. I explained the inadmissibility of such cases and their implications. I think Albert made the correct conclusions and will be accurate in future. Unfortunately, I was informed about incident only after the ratings been updated.

Taking into account large number of participants who didn't notice the issue, who solved problems completely independently, who were happy of upset by their rating changes, shared their results in social networks it does not seem respectful to do to them unrated. I share the view that it would be better not to be so, but history has already taken place. Note that if I learned the situation during the round or immediately after, the outcome might be different. I think it's a good idea to report suspected cases through questions to give a chance the coordinator or me react quickly.

As a conclusion, I do not propose to raise the tragedy, coordinators do not despair. The writers, of course, need to understand the responsibility and importance of taking on the role. Thousands of participants come to solve your problems and, of course, expect something interesting and new.

I urge the community not to forget about respect for the work of authors: to prepare the contest is a big and difficult task. The author takes on a difficult role and if a round took place, so the hard way from the idea to the final implementation has done. Please, be grateful for it, say the authors, coordinators and testers, thank you!

Whatever effort the Codeforces team makes, we can not do rounds without the writers. Therefore, we look forward to your problems. Hope to see good and bright rounds here!

Thank you for attention,
MikeMirzayanov

Hello, my dear lovers of algorithms and data structures.

Codeforces Round 380 will start on November 20 (Sunday), 09:05 (UTC). It will be based on Technocup 2017 Elimination Round 2. So, if you are a Russian-speaking high-school student, please take part in the Technocup 2017.

Many thanks to KAN, GlebsHP, fcspartakm, Levshunovma. Hope to extend the list soon because of testers. Also some problem ideas are mine.

I hope you will like problems. It will be 6 problems in each division.

Good luck and bugless code

Scoring:

• TK Elim 2 and Div 2: 500-1000-1750-1750-2000-2500
• Div 1: 750-750-1000-1500-2000-2500

UPD 1: Here are our winners!

Top-5 in the Technocup stage:

1. sslotin
2. Arthur
3. hloya_ygrt
4. asokol
5. Denisson

Top-5 in Div.1:

1. riadwaw
2. MrDindows
3. Belonogov
4. dreamoon_love_AA
5. LHiC

Top-5 in Div.2:

1. Ralsei
2. NotDeep94
3. ecvlco397
4. kongroo
5. meeeep

Welcome to 2016-2017 CT S03E09: Codeforces Trainings Season 3 Episode 9. The training duration is 5 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 available as a virtual contest for whose of you who can't take part today. Please, do not cheat. Only fair play!

Visit Codeforces::Gym to find the contest and register.

We are planning to start on November 9, 2016 13:10 (UTC).

It is possible that the problems will be too easy for some participants, it is possible that we will add some problems.

Good luck!

Hello everybody!

The contest is over, and I've found that there is no post about the contest. I'm waiting for unfreeze of http://opentrains.snarknews.info/~ejudge/res/res10355 Who knows the expected time?

Let's discuss problems here.

Also it is interesting how good was the onsite in Novosibirsk. What impressions?

Welcome to 2016-2017 CT S03E08: Codeforces Trainings Season 3 Episode 8 - 2005-2006 ACM-ICPC, Tokyo Regional Contest + 2010 Google Code Jam Qualification Round (CGJ 10, Q). The training duration is 5 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 available as a virtual contest for whose of you who can't take part today. Please, do not cheat. Only fair play!

Visit Codeforces::Gym to find the contest and register.

We are planning to start on November 2, 2016 13:10 (UTC).

It is possible that the problems will be too easy for some participants, it is possible that we will add some problems.

Good luck!

Welcome to 2016-2017 CT S03E07: Codeforces Trainings Season 3 Episode 7 - HackerEarth Problems Compilation. The training duration is 5 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 available as a virtual contest for whose of you who can't take part today. Please, do not cheat. Only fair play!

Many thanks to Errichto for the preparation of the training. He has saved me!

Visit Codeforces::Gym to find the contest and register.

We are planning to start on October, 26, 2016 13:10 (UTC).

It is possible that the problems will be too easy for some participants, it is possible that we will add some problems.

Good luck!

UPD: The training is over. Many thank to HackerEarth for problems! Undoubtedly Errichto is my hero of the day — he've prepared the training! Special thanks to the problem writers.

The editorial is in the comment http://mirror.codeforces.com/blog/entry/47985?#comment-322692

Today 2016-2017 ACM-ICPC, NEERC, Southern Subregional Contest will be held. On behalf of jury and hosts I wish teams to make happy their coaches!

You can watch the results by the link https://contest.sgu.ru/monitor/1.

And on Sunday (October, 23) on 08:00 (UTC) we will host unofficial online mirror. Interesting problems are waiting for you. Judges tried to prepare problems of wide difficulty range: for newcomers and for expirienced teams. This will be a team/personal contest on Codeforces, with teams consisting of up to three people or individual participants. The contest will not affect Codeforces ratings.

For sure, it will be unrated contest. We recommend you to take part in teams. I think, the contest will be moved to Gym later.

Good luck!

MikeMirzayanov, head of judges.

Hello, my dear Codeforcers!

Technocup is the olympiad for Russian-speaking highschool children. The winners will get significant benefits to enroll at Russian universities.

But it become open for everyone! Even if you are not a Russian-speaking highschool children, you can register for unofficial (out-of-olympiad) participation. The problems will be translated to English.

The contest starts on October 15, 09:05 (UTC). It will contain 6 problem to solve.

It will be rated round for:

• official Technocup participants
• unofficial participants from Div. 2

The contest will be hosted according Codeforcers rules.

UPD 1: The scoring is 1000-1000-1500-1500-2500-3000.

Welcome to 2016-2017 CT S03E06: Codeforces Trainings Season 3 Episode 6. The training duration is 5 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 available as a virtual contest for whose of you who can't take part today. Please, do not cheat. Only fair play!

Visit Codeforces::Gym to find the contest and register.

We are planning to start on October, 12, 2016 13:10 (UTC).

It is possible that the problems will be too easy for some participants, it is possible that we will add some problems.

Good luck!

Welcome to 2016-2017 CT S03E05: Codeforces Trainings Season 3 Episode 5 (2016 Stanford Local Programming Contest, Extended). 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 available as a virtual contest for whose of you who can't take part today. Please, do not cheat. Only fair play!

Visit Codeforces::Gym to find the contest and register.

We are planning to start on October, 5, 2016 13:10 (UTC).

It is possible that the problems will be too easy for some participants, it is possible that we will add some problems.

Good luck!