Hello, Codeforces!

We (Denisov, Karavaiev, perekopskiy) are glad to introduce to you Codeforces Round 660 (Div. 2), which will happen on Jul/30/2020 17:35 (Moscow time). The round will be rated for the participants with rating lower 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:

• adedalic for amazing coordinating and reviewing the round, as well as helping with many different things.
• Karavaiev, perekopskiy for creating problems and preparation.
• dorijanlendvaj, Tlatoani, BOGDAN_, oknehcajd, awoo, antontrygubO_o, Osama_Alkhodairy, coderz189, errorgorn, ilyasiv, Tathagat_shah, ermakov22 for testing and providing invaluable feedback.
• MikeMirzayanov for Codeforces and Polygon platforms.

There will be 5 problems and 2 hours to solve them.

We really hope you enjoy our first contest!

UPD: Here is the score distribution:

750—1000—1500—2000—2750

UPD: Editorial is published!

UPD: Congratulations to the winners!

Div. 1:

1. neal

2. Um_nik

3. heno239

4. jiangly

5. dreamoon_love_AA

Div. 2:

1. okikust

2. SpatialMovement

3. laralalala

4. KD-Tree

5. Mai_madarchod_hu

Hello Codeforces!

On Jul/29/2020 17:35 (Moscow time) Educational Codeforces Round 92 (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!

Our friends at Harbour.Space also have a message for you:

Hey Codeforces!

We hope you’ve been doing well these past couples of weeks.

This week, we wanted to share a blog post about two of our students. As you might know, Harbour.Space has a unique approach to education — besides classwork and exams, we encourage our students to develop their skills with hands-on projects or even create their startups, so that they’re ready for the workforce when they graduate.

That’s exactly what Jonathan and Khaled, two of our Data Science students, did.

After working hard on their Machine Learning-based startup, they were selected by the European Organization for Nuclear Research (CERN) for a 5 Week Student Entrepreneurship Programme, and are now preparing to travel to Geneva in October. We summarized the story of how they went from data scientists to startup founders in this article.

We hope it inspires you to pursue your passions, and work collaboratively to improve the world for those around you.

Good luck on your round, and see you next time!

Congratulations to the best hackers:

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

UPD: Editorial is out

Hello!

This is just a small announcement of the latest updates in EDU. New features:

• Now you can view other's solutions if you have solved the problem yourself. I think this can be very useful. When I I was a contest participant, I always looked as others who are more experienced than me wrote this or that code. Often found something interesting and useful.

• Now you can view tests for problems in the format, as it is done in the archive in the main section of the website.

• Now you can hack other people's solutions if you have solved the problem yourself. And fun and will improve tests of these problems.

More about EDU section you can read in this post.

And what are your wishes for functionality? I remember about filtering the results of practice by friends.

UPD: And for all practice contests I have set a policy of "use time limits scaling policy". This is a recent innovation — you can use it for educational contests, the system will automatically increase the time limit for some languages. Recommended for use only in educational contests.

Hello, Codeforces!

I'm very glad to invite you to the first Cuban round Codeforces Round 659 (Div. 1) and Codeforces Round 659 (Div. 2) which will take place on Jul/24/2020 17:35 (Moscow time).

All problems in this round were created and prepared by mnaeraxr, gilcu3, dcordb, jcg and me. We tried to make them interesting and diverse and hope that you will enjoy them!

You will be given 2 hours to solve 6 problems in both divisions, and we highly encourage you to read all of them :)

We would like to thank:

• antontrygubO_o for amazing coordination of this round.

• Um_nik, gamegame, ffao, eatmore, isaf27, balbit, Tlatoani, prabowo, Kuroni, hugopm, MagentaCobra, qlf9, faremy, golions for testing the problems and providing invaluable feedback.

• MikeMirzayanov for providing Codeforces and Polygon platforms.

The score distribution will be announced shortly before the round (or earlier).

UPD: Here is the score distribution:

Div2: 500 — (500 + 750) — 1750 — 1750 — 2500 — 2500

Div1: 1000 — 1000 — 1750 — 1750 — 2000 — 2250

Good luck and have fun!

UPD: The editorial is ready Editorial

UPD: Congratulations to the winners!

Especially for tourist, Benq and Radewoosh who solved all the problems!!!

Div. 1:

1. tourist

2. Benq

3. Radewoosh

4. ksun48

5. jiangly

6. yosupo

7. ecnerwala

8. Egor

9. Marcin_smu

10. ainta

Div. 2:

1. AhoCorasick

2. okikust

3. crystal302

4. ServantSaber

5. Kirill_Kudr22

6. RunMIT

7. tripPple_A

8. CodeSlayer4425

9. ZADaCHI

10. ITO

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.