Hey everybody!

We (MagentaCobra, Tlatoani, golions, qlf9) are super excited to invite you to take part in Codeforces Round #655 (Div. 2), which will happen on Jul/11/2020 18:05 (Moscow time). Please note the unusual start time. The round is rated for users with rating strictly less than 2100, although higher rated users are more than welcome to take part out of competition.

Huge thanks to those who helped make this round possible:

• Tlatoani, golions, qlf9 for creating problems and preparation
• antontrygubO_o for r̶e̶j̶e̶c̶t̶i̶n̶g̶ ̶m̶o̶s̶t̶ ̶o̶f̶ ̶o̶u̶r̶ ̶p̶r̶o̶b̶l̶e̶m̶s̶ coordinating our round
• gamegame, dorijanlendvaj, thenymphsofdelphi, aryanc403, Ari, alireza_kaviani, KonaeAkira, Mn619, AmShZ, smax, galen_colin, cuber_coder, gabrielwu, nvmdava, 300iq, Monogon, Mohamed.Sobhy, kefaa2, pajenegod, Devil, Osama_Alkhodairy, Mohammad_Yasser, Taran_1407 for testing and providing invaluable feedback
• MikeMirzayanov for Codeforces and Polygon platforms
• You for participating in our contest :)

There will be 6 problems and 2 hours to solve them.

We really hope you enjoy our first contest!

Hi!

On Jul/04/2020 17:45 (Moscow time) we will host Codeforces Global Round 9.

It is the third round of a 2020 series of Codeforces Global Rounds. The rounds are open and rated for everybody.

The prizes for this round:

• 30 best participants get a t-shirt.
• 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive.

The prizes for the 6-round series in 2020:

• In each round top-100 participants get points according to the table.
• The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest.
• The best 20 participants over all series get sweatshirts and place certificates.

Thanks to XTX, which in 2020 supported the global rounds initiative!

The problems of this round were prepared by a team of authors: adamant, antontrygubO_o, Ari, dengyaotriangle, hugopm, Kuroni, MrDecomposition, and Ynoi. We would like to thank the following people:

• Our fantastic army of testers: aryanc403, abhayps, DeadlyCritic, Priyank, benson1029, 300iq, Guendabiaani, Arayi, thenymphsofdelphi, Monogon, ainta, Elegia, Prabowo, spacewalker, ko_osaga, kefaa2, gnomina007, MiFaFaOvO, Aaeria, teekteek, manjpatel, Almypa, tfg, and tzuyu_chou for helping greatly in improving this round's balance and quality!

• gamegame and dorijanlendvaj, for their help in improving the humor of the round.

• MikeMirzayanov for the Codeforces and Polygon platforms.

You will be given 2 hours and 30 minutes to solve 9 problems, and we highly encourage you to read all of them :)

To save testers the work of writing their opinion in the comments, we have compiled some of their opinions for them!

Good luck!

UPD: Score distribution:

500 — 750 — 1500 — 1750 — 2000 — 2000 — 2250 — 2750 — 4000

UPD2: Editorial

UPD3: System tests have finished, congratulations to the winners!

1. tourist
2. scott_wu
3. yosupo
4. Um_nik
5. tEMMIE.w.
6. lqs2015
7. heno239
8. Motarack
9. zeronumber
10. ltst

UPDATED

Dear participants!

Congratulations on joining the ICPC 2020 Graph Mining Challenge powered by Huawei! All were truly amazed by the participation and quality of the solutions. Congratulations to all of the winners! You will be contacted soon about your prizes.

The competition was so fierce that ICPC U and Huawei have decided to keep the fun going by starting a new, one-week challenge with all new prizes. The problem and graphs are the same, so you can build on your previous success. All are encouraged to participate in this challenge. You may only win one prize from the entire ICPC Graph Mining Challenge events (all combined). If you place in multiple challenges, you will be able to pick the prize you prefer.

Many of you might have been following the Challenge tutorials on ICPC U page. If you didn’t — we’re delighted to invite you to do so in order to sharpen your problem-solving skills and applying it during this additional ICPC challenge week.

As always, ICPC U invites everyone to Train, Practice, and Perform!

Codeforcesの皆さん、こんにちは!(Hello, Codeforces!)

I'm glad to invite you to my first contest, Codeforces Round #654 (Div. 2) which will be held on Jul/01/2020 16:35 (Moscow time) (notice earlier time than usual). All of the problems were mainly written and prepared by me. The round is rated if your rating is strictly less than 2100.

You will be given 6 problems (one problem has a subtask) and 2 hours to solve them. Please, read all the problems.

I would really like to thank:

• isaf27 for amazing coordinating my round.
• 300iq , alireza_kaviani , AmShZ , antontrygubO_o , dorijanlendvaj , lucky_21 , Monogon , noobiesAG , sibasish_14 and zxyl for mighty testing the problems.
• MikeMirzayanov for marvelous Codeforces and Polygon platforms.

The scoring distribution will be announced later.

Good luck, have fun and wish your high ratings :)

UPD: Scoring distribution : $$$500 - 1000 - 1250 - 1500 - (1500 + 1250) - 3000$$$

UPD: Editorial is out

Hello Codeforces!

In February, in the Russian-language interface, we announced a new educational subsection of the website. It's time to go international!

I am pleased to invite you to test the new section, which so far has the working title EDU. I hope that someday EDU will become a real educational hub for fans of programming competitions. It will be great to have in one place the collected educational content with text and video materials, with selected thematic problems.

At the moment, its functionality is still under development, and here is the current progress and β-testing preview. Write your comments and suggestions in the comments here.

So far, only a pilot course with the first lesson "Suffix Array" has been presented to your attention. The plans include expanding both the functionality of the section and filling it with new content.

Russian version already contains more lessons. At the moment, it is important for us to get the first feedback from international users. Many thanks to Pavel Mavrin (pashka) for preparing the first English lesson. Please support pashka to motivate him to translate more lessons!

I hope that in the future, using the materials in this section, you will be able to gain knowledge on an extensive set of topics that are used in contests and olympiads. According to the current plan, a group of ITMO lecturers and students will be engaged in a pilot course, a little later we will consider the possibility of opening the possibility of creating classes for a wider audience.

Thanks to ITMO University for the idea and support for the implementation of this initiative!

Welcome to the Summer Programming School "Volga Camp"! Volga Camp is a school targeting algorithms, data structures and special mathematical chapters for school students of the 7th grade and older. Here you can get invaluable experience and prepare for programming competitions.

The School was to be held near Kostroma, on "Berendeyevy Polyany" recreation department. But this year it will be held online from July 21 to August 4.

There will be 5 separate programs, each having a different difficulty level. The first 4 programs will be held in Russian and the 5th — in English. The registration for Russian programs is closed.

The School is conducted by the ACM MISIS competitive programming centre in collaboration with teachers and graduates of school 179, students and teachers of FCS HSE and DIHT MIPT.

To participate you need to get registered here and then go through a selection process in the form of online competition. The selection contest will be open for 48 hours on July 11-12 (you can write it at a time convenient for you). The Participation fee is 200 €. And we have a special discount for students from developing countries except China, as our project has recently received some sponsor help. For participants from these countries the fee will be reduced to 50 €. Find more information on our official web page: https://volgacamp.ru/en/school

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Hello! Codeforces Round #653 (Div. 3) will start at Jun/28/2020 17:35 (Moscow time). You will be offered 6 or 7 problems (or 8) with expected difficulties to compose an interesting competition for participants with ratings up to 1600. However, all of you who wish to take part and have rating 1600 or higher, can register for the round unofficially.

The round will be hosted by rules of educational rounds (extended ACM-ICPC). Thus, during the round, solutions will be judged on preliminary tests, and after the round it will be a 12-hour phase of open hacks. I tried to make strong tests — just like you will be upset if many solutions fail after the contest is over.

You will be given 6 or 7 (or 8) problems and 2 hours to solve them.

Note that the penalty for the wrong submission in this round (and the following Div. 3 rounds) is 10 minutes.

Remember that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsporting behavior. To qualify as a trusted participants of the third division, you must:

• take part in at least two rated rounds (and solve at least one problem in each of them),
• do not have a point of 1900 or higher in the rating.

Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600, then the round will be rated for you.

Thanks to MikeMirzayanov for the platform, help with ideas for problems and for coordination of my work. Thanks to my good friends Daria ZeroAmbition Stepanova, Mikhail pikmike Piklyaev, Maksim Ne0n25 Mescheryakov and Ivan BledDest Androsov for help in round preparation and testing the round. Also thanks to Artem Rox Plotkin and Dmitrii _overrated_ Umnov for the discussion of ideas and testing the round!

Good luck!

</almost-copy-pasted-part>

UPD: Also thanks to ma_da_fa_ka for testing the round and special thanks to Dmitrii _overrated_ Umnov, Artem Rox Plotkin and, of course, Mike MikeMirzayanov Mirzayanov for discussing ideas and great help with round preparaion!

UPD2: Editorial is published!

UPD: You can predownload tests as an encrypted zip-archive by the links https://test1.codeforces.com/icpc-challenge-2020-tests.zip or https://test4.codeforces.com/icpc-challenge-2020-tests.zip (~80MB). The password is 64e00d81811bbc463e1e636af.

Hello everyone!

Live broadcast

Announcing the ICPC Graph Mining Challenge, Powered by Huawei and brought to you by ICPC U. Graphs are a powerful mechanism for representing many aspects of our daily lives, from mobile call routing to disease tracking. Answering various graph-related questions enables solutions to some of the most challenging, modern problems. The ICPC Challenge presents a problem from some area in computing. The area and problem style may be very different from the standard ICPC problems. Previous contests included new programming languages, multi-agents, parallel programming, etc. The ICPC Challenge provides a platform for ICPC to experiment with new problem types. It also provides participants with experience in some new area and problem type.

The ICPC Graph Mining Challenge will take place online during ICPC Day Zero on 27 June, 2020, 11:00-14:00 UTC. This round is unrated for all participants. Day Zero is a celebration of the 2020 ICPC World Finals, hosted by the Moscow Institute of Physics and Technology (MIPT). Everybody is welcome to participate. This is an individual competition. Participants will be divided into three groups: 2020 ICPC World Finals Contestant, 2020 ICPC World Finals Coach (includes co-coaches), and Participants. The 2020 ICPC World Finals Contestants and Coaches with the best graph solutions will be recognized as ICPC Challenge Winners. The top-scoring participants will also receive great prizes.

Huawei will provide prizes to the 12 winners in each group accordingly:

• Group 1: 3 hour Challenge — ICPC 2020 World Finalists
• Group 2: 3 hour Challenge — ICPC Coaches and Co-Coaches
• Group 3: 3 hour Challenge — All participants

Each participant may win at most one prize for this Challenge.

All participants must agree to follow the 2020 ICPC Graph Mining Challenge Rules.

Participation Instructions:

1. Read and agree to follow the rules.
2. Create a Codeforces account if you don’t already have one.
3. Associate your Codeforces account with your ICPC account if you have one. Though optional, this is necessary if you want to compete as a 2020 ICPC World Finalist or Coach.
4. Register for the contest here.
5. Please, make sure to complete the Warm-up at least 24 hours before the event to test your access, etc.
6. There will be large input files. They will be available here at least 24 hours in advance. We recommend you to download them before the event.
7. Go here at least 20 minutes prior to the start of the contest.

Good luck to all participants!

Hello Codeforces!

On Jun/25/2020 17:35 (Moscow time) Educational Codeforces Round 90 (Rated for Div. 2) will start.

Series of Educational Rounds continue being held as Harbour.Space University initiative! You can read the details about the cooperation between Harbour.Space University and Codeforces in the blog post.

This round will be rated for the participants with rating lower than 2100. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.

You will be given 6 or 7 problems and 2 hours to solve them.

The problems were invented and prepared by Roman Roms Glazov, Adilbek adedalic Dalabaev, Vladimir vovuh Petrov, Ivan BledDest Androsov, Maksim Ne0n25 Mescheryakov and me. Also huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Good luck to all the participants!

Congratulations to the winners:

Congratulations to the best hackers:

And finally people who were the first to solve each problem:

UPD: Editorial is out

Hi community,

I'm glad to invite you to my first contest, Codeforces Round #652 (Div. 2) which will be held at Jun/23/2020 17:05 (Moscow time) ($$$\text{notice the unusual time}$$$). The problems are mainly prepared and invented by me. The round is rated for participants with rating strictly less than $$$2100$$$, others are able to take part in the round out of competition. You will be given $$$2$$$ $$$\text{hours}$$$ to solve $$$6$$$ $$$\text{problems}$$$.

Firstly I'd like to thank adedalic for coordinating and reviewing the round, as well as helping with many different things.

I'd like to thank antontrygubO_o, physics0523, McDic, Ashishgup, dannyboy20031204, Kuzey, Return_0, FieryPhoenix, ma_da_fa_ka, ITDOI, AM_I_Learning, pikmike, lynmisakura, JustasLe and ArimeZ for testing the round and giving valuable feedback.

Also I'd like to thank coauthors, amiralisalimi, AS.82 and davooddkareshki for helping me with inventing and choosing the problems.

Finally, thanks to MikeMirzayanov for very nice and convenient Codeforces and Polygon platforms.

I wish you all will find the problems interesting, thank you for participating, and good luck!

$$$\text{Scoring distribution : } \; 500 ~- 1000 ~- 1500 ~- 2000 ~- 2500 ~- 3000$$$

$$$\textbf{UPD}$$$ : Editorial is out