On Oct/25/2018 17:35 (Moscow time) Educational Codeforces Round 53 (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 extented ACM 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 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 and me.

Good luck to all participants!

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

Hey Codeforces! We want to remind you that the Scholarship for the Master’s in Robotics programme, which starts on January 7th 2019, has an application deadline of November 12th, 2018.

Harbour.Space University and Remy Robotics are collaborating to offer graduate students from anywhere in the world a once in a lifetime opportunity, a fully funded scholarship for Harbour.Space University’s Master’s Programme in Robotics.

The scholarship value is €34.900 and it includes:

• Complete coverage of the University tuition fee (€22,900)

• Internship at Remy Robotics (20h per week during 1 year)

• €1,000 per month during 1 year (Internship earnings)

UPD: vovuh and me will be waiting for you on the community Discord server shortly after the contest to discuss the problems.

Congratulations to the winners:

Congratulations to the best hackers:

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

UPD2: Editorial is published

part 2: https://codeforces.net/blog/entry/62792

Watch my lecture-stream tomorrow (Thursday) at 14:00 CEST — https://www.youtube.com/watch?v=qdlPY37MBPo https://www.youtube.com/watch?v=U_h3IjreRek. I will go through theory and problems from this blog. The only prerequisite is knowing what is probability. The next (harder) part on Monday.

The video will be available later, with timestamps for each problem — so you don't have to watch everything.

Definition of EV

Let's say we bought a lottery ticket for 2$. We will win 10$ with probability 10%, and 20$ with p-bility 2%. On average, it gives us 0.1·10 + 0.02·20 = 1.4, so we are worse off after buying the ticket. The computed average is called the expected value.

The expected value (EV, expectation) is the average value of an event/experiment. For example, EV of the number of pips rolled on a 6-sided die is 3.5:

Linearity of EV (super important theorem):

I would like to invite you to participate in the rated Codeforces Round #518. Date and time of the round: Wednesday, October 24, 2018 at 18:05. The round was postponed from October 23 to October 24 because of the ICPC Indian Online Qualifier.

This is the first competition I proposed. I hope you will enjoy it.

The round will have 6 tasks for the second division and 5 tasks for first (3 problems are common). The contest will last for 2 hours.

Tasks for you were prepared by Alexey kristevalex Kristev and Alexey Um_nik Danilyuk. Also thanks for:

Nikolay KAN Kalinin and Ildar 300iq Gainullin for help in preparing the problems; Ivan isaf27 Safonov и Oleg Merkurev Merkurev for testing the round; Mike MikeMirzayanov Mirzayanov for Codeforces and Polygon platforms.

I would like to express a special gratitude to Um_nik for the help throughout the process of preparing the round and also for patience for my stupid questions.

This round is a thanks-round for support from Mail.Ru during the 8-year campaign!

Scoring distribution will be announced later. I wish you a high rating and looking forward to see you at the competition!

I'll be on the community Discord server shortly after the contest to discuss the problems.

UPD: scoring distribution div1: 500 1000 1750 2250 2500 div2: 500 1250 1500 2250 2750 3500

UPD2: edtorial.

Hello, codeforces!

Sorry for the long break, but the last weeks of holidays and the first weeks of academic year took my attention. I hope today's trick will make you forgive me. :P

I invented this trick a few years ago, but for sure I wasn't first, and some of you already know it. Let's consider the following interactive task. There are n (1 ≤ n ≤ 10⁵) hidden integers a_i, each of them from range [1, 10¹⁸]. You are allowed to ask at most 103000 queries. In one query you can choose two integers x and y (1 ≤ x ≤ n, 1 ≤ y ≤ 10¹⁸) and ask a question ''Is a_x ≥ y?'' The task is to find the value of the greatest element in the hidden array. The checker isn't adaptive.

Unfortunately, this task is only theoretical, and you cannot solve it anywhere, but it'll turn out, that solution can be handy in many other, much more complicated problems.

Hi all!

This weekend, at Oct/21/2018 11:10 (Moscow time) we will hold Codeforces Round 517. It is based on problems of Technocup 2019 Elimination Round 2 that will be held at the same time.

Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at Technocup 2019 website and take part in the Elimination Round.

Div. 1 and Div.2 editions are open and rated for everyone. Register and enjoy the contests!

The round authors are Kostroma, Golovanov399, komendart, Denisson and Dashk0.

Have fun!

The round is over, congratulations to the winners!

Technocup 2019 - Elimination Round 2

1. Holidin
2. receed
3. Sonechko
4. radoslav11
5. scanhex

Codeforces Round 517 (Div. 1, based on Technocup 2019 Elimination Round 2)

1. Radewoosh
2. ainta
3. 300iq
4. TLE
5. RAVEman

Codeforces Round 517 (Div. 2, based on Technocup 2019 Elimination Round 2)

1. cz_yixuanxu
2. orbitingfIea
3. I_Love_Irelia
4. djq_fpc
5. buaads

The editorial is published.

Hello!

ACM-ICPC Southern Subregional Contest (NEERC/Northern Eurasia) 2018 has ended on October 16. There were 72 teams onsite in Saratov, most of them were invited because of their result on the qualification stage.

On Oct/20/2018 11:05 (Moscow time) will start online-mirror 2018-2019 ICPC, NEERC, Southern Subregional Contest (Online Mirror, ACM-ICPC Rules, Teams Preferred).

In this contest I play a role of Cheif Judge and the jury teams consists of ex-participants of ICPC from Saratov and jury members from other cities. Many thanks to all of them! I hope you will like the problems!

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

MikeMirzayanov

Hi all!

I'm happy to welcome you at the Div.1 and Div.2 shared rated round Mail.Ru Cup 2018 Round 1, it will start at Oct/18/2018 19:35 (Moscow time). The problems were prepared by me — Ivan Safonov. I'd like to thank Dmitry cdkrot Sayutin for an idea and preparation of one of the problems and Egor peltorator Gorbachev for an idea for another one.

This round is the first round if the new championship called Mail.Ru Cup, you can learn more about it following the link. The round will be rated for everybody!

The championship feature the following prizes:

• First place — Apple MacBook Air
• Second and third place — Apple iPad
• Fourth, fifth, sixth places — Samsung Gear S3
• Traditionally, the top 100 championship participants will get cool T-shirts!

In each round, top 100 participants get prize points according to the table. The championship's result of a participant is the sum of the two largest results he gets on the three rounds.

Huge thanks to Grigory vintage_Vlad_Makeev Reznikov and Ilya izban Zban for testing the problems, to Nikolay KAN Kalinin and Ildar 300iq Gainullin for their help in preparation, and to Mike MikeMirzayanov Mirzayanov for Codeforces and Polygon platforms.

The round will feature eight problems to solve in two and a half hours. The scoring will be announced closer to the beginning of the round.

I hope everyone will find some problems interesting. I wish everybody a successful round and a positive rating change!

Good luck!

UPD1，Scoring distribution:

500 750 1250 1500 2000 2250 3000 4000

Congratulations to the winners of Round 1!

1. mnbvmar
2. Um_nik
3. V--o_o--V
4. LHiC
5. Lewin

UPD2

Editorial

Hi everybody,

This Sunday there will be a 16th Moscow Team Olympiad, high school students competition based in Moscow that is an elimination contest for All-Russian Team Olympiad. This contest is prepared by Moscow Olympiad Scientific Committee that you may know by Moscow Open Olympiad, Moscow Olympiad for Young Students and Metropolises Olympiad (rounds 327, 342, 345, 376, 401, 433, 441, 466, 469, 507).

Round will be held at 10:05 UTC on Sunday and will last for 2 hours. Each division will have 6 problems.

Problems are prepared vintage_Vlad_Makeev, Glebodin, Andreikkaa, qoo2p5, mingaleg, Flyrise, cdkrot, achulkov2, grphil, Sehnsucht, Aphanasiy, Sender, DebNatkh, GreenGrape under my supervision with great help of GlebsHP, meshanya, Endagorion, Zlobober and Helen Andreeva.

Thanks to cdkrot for the round coordination and statement translation, and also thanks for MikeMirzayanov for systems codeforces and polygon, which was used to prepare problems of this olympiad.

Good luck everybody!

UPD1: The scoring distribution will be:

500 — 1000 — 1000 — 1500 — 2000 — 2500 for div. 1.

500 — 1000 — 1500 — 2000 — 2000 — 2500 for div. 2.

UPD2: Editorial

UPD3: Winners:

Div. 1:

1. mnbvmar
2. bmerry
3. jcvb
4. TLEwpdus
5. WA_TLE

Div. 2:

1. Ebola_Emperor
2. Orange_User
3. orbitingfIea
4. little_waxberry
5. fnch

Hi Codeforces!

For you, perhaps it was yet another Codeforces round. But not for me. Codeforces Round 515 (Div. 3) is the first round tested on new judging servers at ITMO University. And this is not just an update of location. Ta-dam! Now your solutions will be judged on the new Intel i3-8100 processors. And this is not all news. The number of judging servers has increased, which means fewer queues during rounds!

I am pleased to announce that now I live in St. Petersburg, I work at ITMO, and Codeforces is gradually moving from the walls of dear to me Saratov University to ITMO University. The decision to move was not easy for me. My plan is that, based on ITMO, I can focus more on Codeforces development and work on the platform. The number of world champions per square meter is simply overwhelming, and working with a large team of such enthusiasts (and professionals!) of sports programming, like me, is extremely inspiring. I always liked St. Petersburg and the atmosphere of ITMO. Intuition did not let me down. I feel surrounded by people close to me in spirit (and I’m not only talking about a work). I am sure there are many interesting common projects ahead!

I do not say goodbye to Saratov. This is my hometown, full of people dear to me. I came to my first programming training at SSU exactly 20 years ago. Antonina Fedorova, thank you very much. Natalya Andreeve, I would like to say a personal thank you now. You have opened for me an interesting world of programming competitions. We were happy together when we first advanced to the ICPC Finals, and later when we became champions of Russia and the World. We made countless competitions and helped many Saratov students find themselves in programming. I fervently support the future of the Programming Competitions Training Center at SSU and future generations of Saratov contest participants. And now, I am in Saratov and still the head of the jury of the ICPC Subregional Contest, and even an SSU employee. I hope that we will make a good and interesting contest.

I will try to make a complete relocation of the Codeforces infrastructure to ITMO without downtimes. A good Internet connection between SSU and ITMO is encouraging. All the planned work will adapt to the schedule of the rounds, and now it pleases more than ever (I send my greetings to the coordinators!).

Currently, all Codeforces and Polygon solutions are being judged on new servers based on Intel i3-8100 processors. Fortunately, the performance of a single core is not very different from the one that the old generation of judging servers had. Thus, the time limits in all problems remain the same.

Such news. I am waiting for you on Codeforces Round #516 (by Moscow Team Olympiad).

— MikeMirzayanov

Mail.Ru Group together with Codeforces invites everyone to take part in the new Mail.Ru Cup competitive programming championship.

Rules

The championship is holding on the Codeforces platform in the format of four rounds: one practice round and three main rounds. Each round is open to all comers. There are no restrictions on participants in any of the rounds.

The practice round is intended for familiarization with the championship platform, participation in it is optional, the results of performances in the practice round do not affect the results of participation in the championship. It is unrated, the duration is 72 hours.

All three main rounds are independent, the results of participation in each of it do not affect the possibility of participation in next rounds. A competitor may take part in any number of main rounds. Each main round lasts 2.5 hours. All of them are open for everyone and rated for all participants.