Hi everyone!

I am happy to invite you to take participation in the online mirror of the Baltic Olympiad in Informatics 2020 to be held on Jul/22/2020 14:05 (Moscow time) and Jul/23/2020 14:05 (Moscow time) on Codeforces!

The Baltic Olympiad in Informatics 2020 (BOI 2020) is an individual contest for secondary school students from eleven countries (in alphabetic order): Denmark, Estonia, Finland, Germany, Iceland, Latvia, Lithuania, Norway, Poland, Sweden and Ukraine. Over 60 secondary school students compete against each other, solving difficult problems of algorithmic nature. Each country sends their top 6 contestants from their national olympiads which take place in the months beforehand. You can check out the official web page at boi2020.lv.

The contest consists of two days; each day the students are given 5 hours to solve 3 problems of various difficulty. Each problem is worth 100 points that are distributed into multiple subtasks with different constraints that allow the participant to earn partial score. For the testing, the IOI grading format is used, where the participant receives full feedback of the execution of the solution on all tests during the contest.

This year the contest was supposed to be held in Latvia, Ventspils, but is not held onsite due to the pandemic, and the students will compete in a proctored setting online. With generous help from MikeMirzayanov, we are glad to also provide the mirror contest at Codeforces for anyone interested.

Note that the contest is not rated. The mirror starts with a delay of 1 day, 1 hour and 5 minutes.

We wish you to enjoy the contest! :)

-- BOI 2020 committee

Martins Opmanis, Rihards Opmanis, Sergey Melnik, andreyv, Pakalns, gen, eduardische, Alex_2oo8, nvilcins, KarlisS.

UPD1: The scoreboard will not be public, each participant will be able to see only the results of their own submissions.

UPD2: Tutorial for Day 1 has been published.

UPD3: Tutorial for Day 2 has been published.

UPD4: Congratulations to full score 600 point winners WZYYN, isaf27, Arpa!

Hello, Codeforces!

I'm very glad to invite you to Codeforces Round 658 (Div. 1) and Codeforces Round 658 (Div. 2). This contest will take place on Jul/21/2020 17:35 (Moscow time). In both divisions, you will have 2 hours to solve 5 problems (and one subtask). The score distribution will be announced closer to the start of the round.

Huge thanks to:

• isaf27 for excellent coordination of this round
• Fanurie, antontrygubO_o, Ari, DeadlyCritic, gamegame, coderz189, hugopm, Kuroni, IaMaNanBord, Priyank, SecondThread, solvemproblr, talibmohd, WNG for testing the problems and providing useful feedback.
• MikeMirzayanov for providing Codeforces and Polygon platforms.

I've worked hard to ensure the pretests are short and the statements are strong. Remember to only read the problems that you can solve, and may you have the best of luck!

Because I know you all have so many questions, I have compiled an FAQueue

• Q: Is it rated?
• A: Yes

UPD Here is the score distribution:

Div. 2: 500 — 1250 — (1000 + 1000) — 2250 — 3000

Div. 1: (500 + 500) — 1500 — 2000 — 2500 — 3000

UPD Editorial

UPD I filled in the answer to the FAQ. Also, congrats to the winners!

Div. 2:

1. badger_champion

2. Mai_madarchod_hu

3. rulai

4. Vimmer

5. niynip

Div. 1:

1. Benq

2. Um_nik

3. KAN

4. Petr

5. ksun48

Hi!

This Sunday will take place All-Russian olympiad for students of 5-8 grades, in the name of Keldysh. Good luck to all the participants! Olympiad is conducted under the guidance of the Moscow Olympiad Scientific Committee, in particular GlebsHP, ch_egor, Endagorion, vintage_Vlad_Makeev, Zlobober, meshanya, cdkrot, voidmax, grphil and, of course, Helen Andreeva.

We are happy to announce the Codeforces Round #657 (Vintage Codeforces Round #3) based on the problems of this olympiad! It will be a Div. 2 round, which will take place at Jul/19/2020 12:00 (Moscow time). You might have already participated in rounds based on the school olympiads, prepared by Moscow Olympiad Scientific Committee (rounds 327, 342, 345, 376, 401, 433, 441, 466, 469, 507, 516, 541, 545, 567, 583, 594, 622, 626) as well as vintage rounds (rounds 626 and 628).

The problems of this olympiad were prepared by DebNatkh, grphil, KiKoS, voidmax, I_love_myself, 300iq, isaf27 under the supervision of grphil.

Thanks ch_egor, vintage_Vlad_Makeev and meshanya for their help in organizing the Codeforces version of this contest and MikeMirzayanov for the Codeforces and Polygon.

Also I would like to thank the Tinkoff company and personally Tatyana TKolinkova Kolinkova for great help with organizing the competition.

Good luck!

UPD1: Scoring distribution: 500 — 750 — 1250 — 1500 — 2500 — (1500 + 1500)

UPD2: Editorial

UPD3: Winners!

Div. 2:

1. purplesyringa
2. yjw0203
3. kaixinqi
4. penguinman
5. Frikkie

Div. 1 + Div. 2:

1. antontrygubO_o
2. risujiroh
3. tmwilliamlin168
4. sansen
5. LayCurse

<too-old-joke-about-copy-paste>

Hello! Codeforces Round 656 (Div. 3) will start at Jul/17/2020 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 nooinenoojno Stepanova, Mikhail awoo Piklyaev, Maksim Neon 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!

</too-old-joke-about-copy-paste>

UPD: Also thanks to infinitepro for help with statements and testing the round!

UPD2: Editorial is published!

Hello everyone!

I just published a new lesson in the EDU section. This is the first part of the lesson about the segment tree.

In this lesson, we will learn how to build a simple segment tree (without mass modifications), and how to perform basic operations on it. We will also discuss some tasks that can be solved using the segment tree.

More about EDU section you can read in this post.

Hope it will be helpful, enjoy!

Hello.

Unfortunately, the Educational Codeforces Round 91 round will be unrated and, actually, it was completely ruined. I don’t understand what happened yet. At some point in time, all systems began to work unstably and actually stopped working. So far I have no understanding what happened. You may have to change the schedule for future rounds. Sorry. We have such a black stripe. Very upset and demotivated.

Mike.

Hello Codeforces!

On Jul/12/2020 17:45 (Moscow time) Educational Codeforces Round 91 (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 Neon Mescheryakov and me. Also huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Good luck to all the participants!

UPD: The contest is delayed by 10 minutes.

Congratulations to the winners:

Congratulations to the best hackers:

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

UPD: Editorial is out

Hey everybody!

We (gotexans, Tlatoani, malachi_toney_goat, qlf9) are super excited to invite you to take part in Codeforces Round 655 (Div. 2), which will happen on 11.07.2020 18:05 (Московское время). 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, malachi_toney_goat, 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, 244mhq, 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!

UPD: Scoring Distribution:

500—1000—1500—2000—2500—3000

UPD: Due to long queue, the round will be unrated. We're extremely sorry this happened, and all of us are sad about it. We hope you will at least enjoy the problems.

UPD: Editorial

TL;DR: ICFP Programming Contest starts next Friday, on July 17. It's an annual open online competition originally developed by functional programmers. It feels like an entertaining 72-hour marathon with unpredictable tasks and experience one could barely express (though participants write long write-ups describing theirs). If you haven't participated in ICFP Contest — definitely give it a try this year. Register at the website and follow on Twitter.

Unlike other competitions, to participate in ICFP Contest one gathers a team of any size. In 2019, there were teams up to 12 people with a median of 3. The team has 72 hours to crack a single task which is always unpredictable, complicated, and versatile.

For example, in 2018 the task was to optimize 3D printing conducted by a swarm of nano bots, Here's an impressive solver visualization by team WILD BASHKORD MAGES (Ripatti, LinesPrower et al.):

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, enoone, 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, 244mhq, tranquility, EvenImage, 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. heuristica
6. lqs2015
7. heno239
8. Motarack
9. zeronumber
10. Itst_boyfriend