Hi, Codeforces!

This is not an ordinary post from me. This is not an announcement of new features or a championship, but I'm no less enthusiastic.

I am glad to inform you that from January 29 to February 16, 2018 I will be giving the course "Advanced Algorithms and Data Structures" in Harbour.Space University (Barcelona, Spain). The course will be in English. The students of this course will not only be students of Harbour.Space, but is open to all! Who wants to join?

This course isn't just for Harbour.Space students, it is also open to Codeforces participants, who will be offered a special price, 1000 EUR. The cost does not include travel or accommodation.

In my plans there is a detailed story about some algorithms and data structures, a lot of practical exercises and emphasis not only on the correctness, but also the beauty and structure of the code. My goal is to make useful and interesting classes for both those who want to understand the fundamental CS, and for those interested in programming competitions. And of course, we will have the opportunity to meet and talk. I'm happy to share stories about the history of Codeforces and development plans.

The course will consist of three weeks of training, 5 training days in each week. The program includes daily lectures and practical exercises. It will not be boring for sure!

Here is the expected course outline:

Harbor.Space University is located in Barcelona (Spain). For users of Codeforces, Harbour.Space is known for active participation in the life of the community of sports programming (partnership with Codeforces in the framework of Educational Rounds). The main activity of the university is teaching (there are bachelor's and master's programs) in the following areas:

• Maths as a Second Language
• Computer Science
• Data Science
• Cyber Security
• Interaction Design
• Digital Marketing
• High Tech Entrepreneurship
• FinTech
• BioTech
• Aerospace Engineering
• SuperCities UrbanTech

Register for my upcoming course here.

Mike Mirzayanov

Hello!

I am pleased to report that two rounds of Codeforces have gone quite well in terms of the work of Codeforces, I am very glad about it. These days nights I spent in a profiler, fixing the code, researching the settings of MariaDB.

In addition, I managed to allocate several hours on Sunday (to be honest, until Monday morning) to finish the long-planned innovation.

Meet, diagnostics of solutions in C++!

Many Codeforces visitors are already tired of the questions of less experienced participants: "Why does my solution not work on some test on the Codeforces servers, if I locally launch it and it works correctly? You have the wrong compiler/servers!" In 99% of cases this is an example of undefined behavior in a program. In other words, the program contains mistakes that, due to a number of circumstances, are not reproduced at local launch, but are reproduced at launch on the Codeforces servers.

Sometimes, it's not easy to notice such a mistake. A small overflow of the array can lead to an incorrect answer on the test and to an runtime error of the program.

In g++/clang++ there is a remarkable tools called sanitizers. It's such a way to compile a program in a special mode so that when it's working, it will check it for undefined behavior (and some other errors) and, if any, print them to stderr. The drmemory (it is similar to valgrind, but for Windows) has similar functionality, which starts the program in a special mode to detect errors. With such two diagnostic launches, the performance of the program suffers tremendously (the program is executed 5-100 times slower and requires more memory), but often it's worth it.

Now automatic diagnostics in some cases will prevent a question like "Why does not work ???", indicating the error or its appearance!

If your solution:

• written in C++,
• finishes with a verdict "wrong answer" or "runtime error"
• on this test worked extremely quickly and consumed a little memory,

then it will be restarted using special diagnostic compilers (clang ++ with sanitizers and g++ with drmemory). If an execution error occurs during this launch, the diagnostics log will be displayed in the test details in the "diagnostics" section. Of course, this entry will contain a technical report in English, but often it will indicate to you the error of the program. Often it contains the cause of the mistake and even the source code line. If the diagnostics are not displayed, then at least one condition above is not fulfilled or the diagnostics has not detected any errors.

Example of the diagnostics:  here it is written that there was an array out of range error in the line 78.

Thus, the diagnostics will sometimes help you to find a mistake like "out of bounds error", "signed numbers overflow", "uninitialized variable", etc. Carefully read the diagnosis and do not make such mistakes in the future!

I wish your programs did not fail. I hope the innovation will be useful!

There are big plans as it is useful to apply such diagnostics. Do not go far, wait for news, soon there will be more innovations!

P.S. Also, diagnostic compilers are simply available for use. For example, you can use them on the "Custom invocation" tab. I recall that the program runs many times slower and consumes more memory in diagnostic mode.

The contest is declared unrated. For Technocup, results of this round will be counted for elimination. Also, we plan to hold one more (the fourth) elimination round to compensate this failure. Stay tuned for updates. We apologize for the situation, hope you enjoyed the problems.

Hello.

If you are upset about today round, I understand you. Please, downvote this blog instead of the official announcement. The coordinator, writers and tester did a great job making the round. But technical issues erased their effort.

The chain of technical issues leaded to so bad work of the website. This week our server with Polygon system had broken and Mail.Ru quckly replaced it with another one. I forgot to reconfigure Polygon on the new server and it leaded to 502 during the contest. Also today one Codeforces server stopped to respond and I do not know the reason yet (it is first time issue with this server).

Right now I feel myself very upset and thinking about the way to change an approach to have enough time to setup, monitor and develop the system.

Sorry again about it.

Hello!

ACM-ICPC Southern Subregional Contest (NEERC/Northern Eurasia) 2017 has ended on October 18. There were 73 teams onsite in Saratov, most of them were invited because of their result on the qualification stage.

On Saturday, October 21, 08:05 (UTC) will start online-mirror 2017-2018 ACM-ICPC, NEERC, Southern Subregional Contest (Online Mirror, ACM-ICPC Rules, Teams Preferred).

I invite ACM-ICPC teams and individual participants of Codeforces competitions to take part! Sure, the contest will be unrated.

MikeMirzayanov

Codeforces Round 440 will start on October 15 (Sunday), 08:05 (UTC). It will be based on Technocup 2018 Elimination Round 2. So, if you are a Russian-speaking high-school student, please take part in the Technocup 2018.

Codeforces Round 440 is open and rated for everyone.

Wish you good luck and bugless code.

Editorial is posted.

Congratulations to winners!

Technocup official round:

1. Mikhniuk
2. scanhex
3. Krisha
4. lis
5. FalseMirror

Div. 1:

1. khadaev
2. Errichto
3. eddy1021
4. FizzyDavid
5. fateice

Div. 2:

1. wdmmsyf
2. Legilimens2023
3. destinydrifter
4. oscar114514
5. OMS

Hello, Codeforces!

I'd like to invite you to Codeforces Round #436 (Div. 2). It'll be held on Monday, September 25 on 10:35 UTC and as usual Div. 1 participants can join out of competition. Note that round starts in the unusual time!

This round is held on the tasks of the school stage All-Russian Olympiad of Informatics 2017/2018 year in city Saratov. They were prepared by Perforator, MikeMirzayanov and fcspartakm. Many thanks to the testers: sdya и BledDest, and coordinators KAN and vintage_Vlad_Makeev.

It will be a little unusual round — you will be given six problems and two hours to solve them.

Good luck and have fun!

Congratulations to winners!

Div. 2:

1. zjt_ioi_2019_ak
2. AngusRitossa
3. Jha_The_ME_Coder
4. cxh007
5. Alexxx

Div. 1:

1. Shik
2. dreamoon_love_AA
3. black_horse2014
4. orbitingflea
5. KassiJulgus

Analysis is here.

Welcome to 2017-2018 ACM-ICPC, NEERC, Southern Subregional Contest, qualification stage (Online Mirror, ACM-ICPC Rules, Teams Preferred).

The contest was held yesterday on September 17. Mostly it is focused on the participants of the Div 2.

Note that you can print PDF (English or Russian) with the statements. It will be available on the contest dashboard page on the right.

Good luck!

I apologize to the participants of the round. It happened that I accidentally had run improper script and it rebooted the judging machines. It is very insulting, because most problems were proposed by me and I hoped to host an interesting competition for you. A lot of effort was spent on preparation. Apparently, the mistake of just such a human character happened for the first time. I really hope not to repeat it in the future.

MikeMirzayanov

Want problems? We have some!

Codeforces Round 434 will start on September 17 (Sunday), 13:05 (UTC). It will be based on Technocup 2018 Elimination Round 1. So, if you are a Russian-speaking high-school student, please take part in the Technocup 2018.

Many thanks to KAN, vovuh, Neon, ifsmirnov, irkstepanov and WHITE2302 for their help in round preparation. Some problem ideas are mine.

I hope you will like problems. There will be 6 problems in div. 2 and 5 problems in div. 1.

Wish you good luck and bugless code.

Hello, Codeforces!

I am pleased to announce the 2nd Hello Barcelona Programming Bootcamp in collaboration with Moscow Workshops ACM ICPC, which will be hosted by our partner Harbour.Space University together with Moscow Workshops ACM ICPC, ITMO University, Moscow Physics and Technology University, Saint Petersburg State University and Codeforces!

The boot camp will be held from September 27th to October 5th in Barcelona. This time it will be at the beautiful and technologically mind-bending Media-TIC building — the Smart Building of Tomorrow.

Media-TIC building — the Smart Building of Tomorrow

The world's greatest coaches will be attending: Andrew andrewzta Stankevich, Michael Endagorion Tikhomirov, Gleb GlebsHP Evstropov, Artem VArtem Vasilyev and other world renowned Russian coaches. As a coach, I will come too. The Chief Judge of the camp is Oleg snarknews Khristenko. Seriously, it will be a unique opportunity for teams around the world to learn from such well-known and successful coaches in the ACM-ICPC world.

Having visited the first Hello Barcelona programming Bootcamp in February, I left the event feeling inspired from the overall atmosphere. I am sure that all teams received an immense amount of knowledge and skills. As one of the coaches, all of the flattering reviews about the camp from the participants were pleasant for me to hear. I am very glad that these camps are becoming regular. Harbour.Space University and Moscow Workshops ACM ICPC have done a job worthy of admiration!

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 unchanged: €1270 per person (cultural program, accommodation and half-board meals included).

Single participants and teams must register by July 1st, 2017 to receive the 15% off-Early Bird Discount, or the 20% off-Loyalty Discount, which is awarded to teams that participated in previous Moscow Workshops ACM ICPC boot camps.

You can ask any questions by email: [email protected]

Hope to meet you on the Bootcamp, Mike Mirzayanov

In order to experience the atmosphere of the event, I suggest you familiarize yourself with the photos and videos from the 1st Hello Barcelona programming Bootcamp in collaboration with Moscow Workshops ACM ICPC.

ACM-ICPC World Finals 2017 will begin on May 24, 2017 at 15:00 (UTC). This event is the main event of the year in the world of sports programming!

This year ICPC Regional participation included 46,381 of the finest students and faculty in computing disciplines from 2,948 universities in 103 countries on six continents. A record 50,145 students and 5,073 coaches competed in ICPC and ICPC-assisted competitions this year, setting new records in participation.

Codeforces wishes the teams to show a vivid and interesting contest contest. We wish to find beautiful solutions, write without bugs and enjoy many accepted problems!

Links:

• Current results
• Official website of the championship
• ICPC News (photo, video about the Finals)
• ICPC Live (broadcast and not only)

Hello, Codeforces!

The ACM-ICPC World Finals 2017 event is running now. Tomorrow will be the main contest. During these days the directorate of ACM-ICPC shared some news.

• Let me remind you that this season (2016-2017) is last, when the general sponsor of the championship is IBM. For 20 years, IBM has supported ACM-ICPC, investing millions of dollars annually. Thank you, IBM! At the moment, the model is actively being worked out, when there will be not one general sponsor, but there will be a fund in which several companies will participate. At the opening ceremony the Sport Programming Foundation was mentioned. I believe this Foundation will be the main one for the future seasons of the championship. However, these are not yet close plans.

  It was announced that the next three years the general sponsor of ACM-ICPC will be JetBrains! This is amazing news. Particularly pleased that this is actually a Russian company, and its executive director Maxim Shafirov coached the team of St. Petersburg State University, which became the world champion in 2000! I'm sure that the wonderful development environment from JetBrains in the future finals of the championship will await us as a pleasant bonus.

• There is a reform of the qualifying stages of the championship. For example, now Rissian+ regional contest (NEERC) is not part of the European Regionals, but is a separate league of the Northern Eurasia. In general, eight leagues (read, super-regions) were singled out: Europe, Northern Eurasia, North America, Latin and South America, two leagues in Asia, Africa and probably Australia and Oceania. It is planned that each league will have its own separate finals with medals and the top 12 teams from each league will receive a ticket to the World Finals. While these are still distant plans, but the first steps have already been taken. Discusses its quota on the number of participations in the league finals (3 times).

• Unfortunately, this year a significant part of the teams did not receive a visa at all (5 teams) and a dozen more could not arrive completely because of the visa problems of one of the participants. Saratov State University, apparently, is among them. It was announced the decision to invite to the next Wold Finals without any selections and quota accounting for 5 teams that could not come this year. In addition, it is proposed to give a +1 year to participate (without taking into account any other requirements) to all teams that could not arrive completely.

• The next Finals will be held in Beijing, and a year later — in Kochi (India).

Such news.

Hello!

I'm happy to visit Rapid City and meet so many bright contestants here!

I have Codeforces laptop stickers with me and I'll be glad to give them as small gifts to participants of the World Finals. You can find me (I do not have many stickers, be quick) to get gifts. My friend collects coins, so I'll be glad to receive a coin from your country as a souvenir.

See you. And good luck on the contest!

Mike

UPD Still have few stickers. You have a chance!

Hello, Codeforces!

I'd like to invite you to join in Playrix Codescapes Cup for the both divisions that will be held on May 11 at 18:35 MSK. The round is rated and open for everyone.

Problems are prepared by KAN, Al.Cash, MikeMirzayanov and fcspartakm. Huge thanks to Playrix company for making this round possible. Hope you enjoy the round!

Playrix is one of the leading mobile games development companies in the world. Its distributed team consists of 450 professionals from around the world. The company has released three successful mobile free-to-play games – Township, Fishdom and Gardenscapes. All of the projects have consistently been among the Top 50 Grossing Apps for iOS and Google Play since their release.In 2016, Facebook named Gardenscapes game of the year.

Company is looking for Russian-speaking C++ developers.

Prizes from the Playrix company:

• Top 1: iPadPro 9,7 + PowerBank + T-shirt with logo
• Top 2-5: PowerBank + T-shirt with logo
• Top 6-50: T-shirt with logo
• (New!) Random 5 participants (not from top-50, submitted at least once): T-shirt with logo

Congratulations to the winners!

1. tourist
2. LHiC
3. subscriber
4. W4yneb0t
5. enot110

The problem analysis is published.

Hello!

Are you missing something new? I have something to please you.

Regularly I host some events — Olympiads, onsites, and eventually, examinations and tests for students. On the one hand, Codeforces already offers a unique functionality — groups, the integration with Polygon, the possibility of choosing tasks from the archive and so on. But it doesn’t enough!

Domains for groups

Here is an example of such a group. It is open for all — join it and look: http://example.contest.codeforces.com

Domain

Now when you are editing a group, you can specify its subdomain (from 3 to 20 alphanumeric characters, starts with a letter). When you specify the domain, the group will be accessible by a link http://yourgroupdomain.contest.codeforces.com. According to this link, the following is correct:

• Nothing extra will be displayed — the site contains only the information about competitions and blogs of your group and nothing else.
• All you need to display — is an HTTP access to 77.234.215.194. If you host the official contest, important coaching or examination — block all the rest of the Internet, except for this IP-address.
• Today such groups can only contain private competitions and trainings. For example, you can make your mashup and set it up as you need. Maybe, later we will make something with this restriction, but for now — it is like this.

Permitted subnets for the domain

To be sure that extra people will not click on your link http://yourgroupdomain.contest.codeforces.com, you can block the access to it by IP. Specify the exact IP or subnet address. For example, 188.93.56.35;212.193.32.0/19.

The language of the interface of the domain

Probably, when you host the event, only the English (or only Russian) interface is enough for the participant. Use this setting to select the desired behavior.

Header html

You can change the site header at http://yourgroupdomain.contest.codeforces.com, so that there will be not the familiar logo of Codeforces, but the logo or name of your event. For example, when I host the inter-university Olympiad in Saratov, I set it to <h3>Interuniversity Olympiad on programming 2017 (Saratov)</h3>.

Users of the domain (sidebar)

It is very likely that if you hold an Olympiad or something similar, participants may not have the Codeforces account, the information about participants comes from a separate registration, and you want to see usual names in the interface, such as ‘John Doe, Berliandsky SU, 3 Course’, rather than the participant’s handle.

You can add synthetic users to your group with a domain (using these accounts, you can only log the group through the domain). Use the special function “Users of the domain”. Each line corresponds to one user and must be written in the format: contest ids (separated by commas) | Handle | Password | Name. Here's an example of this setting for the domain example.contest.codeforces.com:

213380 | u01 | 371111 | Petr Korotkevich
213380 | u02 | 627492 | Gennady Soejima
213380 | u03 | 491591 | Makoto Knuth
213380 | u04 | 581711 | Donald Cormen
213380 | u05 | 057259 | Thomas Mitrichev

Yes, you can feel like Peter Korotkevich, log on http://example.contest.codeforces.com, and use the login u01 and the password 371111.

Privacy settings

You have a possibility to set all as you wish. For example, to maximally block the access to the group (only by the domain, do not allow extra users), make the closed’ group, and the policy of registering of its membersonly by invitation`. In this case, only domain users (see the point above) and users invited to the group will be able to access the domain address.

For private contests you can set additional settings:

• Allow practice — whether it is possible to solve problems after the official termination in an informal mode of upsolving.
• Allow virtual participation — whether it is possible to participate virtually after the official termination (or whenever you want, if there is no start time).
• Allow out of competition participation — it is reserved for out of competition participation, while only the users of the domain can be registered as out of competition (for the right users, add the symbol 'o' after the contest id, for example ``213380o | u01 | 371111 | Petr Korotkevich'').
• Allow self-registration — whether it is possible for participant to make a self-registration (if no — register him).
• Allow unregistered users to observe the competition — whether it is possible for the participant of the group who is not registered to a contest enter the contest and see the problems, status, standings, and other details.
• Turn on common status — whether it is possible for participants to see the information about other participants’ submissions, or the information about their own attempts is the only available.
• The duration of freezing and unfreeze time. Be careful during the transfer of the contest — unfreeze time must be changed independently.
• The policy for showing tests. Here are possible options: "do not show at all", "show failed tests of own solutions", "show all tests completely".
• The policy of showing other people's attempts. Here are possible options: "do not show at all", "show to participants who solved the problem," "show to everyone."

April 26, 15:35 (UTC) the second Wild Card Round of VK Cup 2017 will take place.

Participants are invited to achieve progress in solving an unusual problem. VK Cup teams which were advanced to the Round 2 (and didn't advance to the Round 3) will take part in VK Cup 2017 - Wild Card Round 2 officially. In addition, this round will be open to the public for unofficial participation for everybody. Registration will be open for the whole round duration.

The round will be one week long. After the end latest submission (with positive score) of each participant will be judged on system tests.

Good luck!

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?