Hello, Codeforces!

74TrAkToR and I are glad to invite you to our Codeforces Round #750 (Div. 2), which will be held at Oct/24/2021 13:05 (Moscow time). Notice the unusual time of the round. The round will be rated for all the participants with rating strictly less than 2100. At the time of the round the CheReKOSH olympiad will be held, where the problems from this round will be used!

We would like to thank everyone who helped us a lot with round preparation.

• Our coordinators KAN and isaf27 for excellent coordination of the round.
• Our testers Um_nik, Denisson, TadijaSebez, ijxjdjd, Mr.Robot_28, flamestorm, romanasa, hu_tao, QuangBuiYT, m371 for high-quality testing and helpful notes.
• MikeMirzayanov for amazing Codeforces and Polygon platforms.

On the round you will be asked to help characters from animated series Luntik and his friends. You will be given 7 problems, one of which has two subtasks. You will have 2 hours 30 minutes to solve them.

UPD: Score distribution: $$$500-750-1500-1750-2500-(2000+1500)-3250$$$.

We wish everyone good luck!

Hi everybody,

This Sunday there will be a XIX 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, 516, 541, 545, 567, 583, 594, 622, 626, 657, 680, 704, 707, 727).

The round will be held at Oct/25/2021 09:35 (Moscow time) and will last for 2 hours. Note the unusual time of the round. Each division will have 6 problems. The round will be held according to the Codeforces rules and will be rated for both divisions.

We kindly ask all the community members that are going to participate in the competition to show sportsmanship by not trying to cheat in any manner, in particular, by trying to figure out problem statements from the onsite participants. If you end up knowing some of the problems of Moscow Team Olympiad (by participating in it, from some of the onsite contestants or in any other way), please do not participate in the round. We also ask onsite contestants to not discuss problems in public. Failure to comply with any of the rules above may result in a disqualification.

Problems are prepared by LHiC, cdkrot, isaf27, AlesyaIvanova, Tikhon228, voidmax, fedoseev.timofey, KiKoS, NiceClock, 4eT_llpuyHblJl, vintage_Vlad_Makeev and Daria Krokhina under my supervision with great help of GlebsHP, meshanya, Endagorion, Zlobober and Helen Andreeva.

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

Also thanks to napstablook and Anti-Light for providing an additional problems that helped to create (I hope) a balanced problem set for the round

Good luck everybody!

Hi all!

This weekend, at Oct/17/2021 14:05 (Moscow time) we will hold Codeforces Round #749 (Div. 1 + Div. 2, based on Technocup 2022 Elimination Round 1). It is based on the problems of Technocup 2022 Elimination Round 1 that will be held at the same time.

Note the unusual start time of the contest.

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

The Div. 1 + Div.2 edition is open and rated for everyone. Register and enjoy the contests!

The problems were written and prepared by Tlatoani, golions, rabaiBomkarBittalBang, qlf9, and me. We would like to express our thanks for antontrygubO_o, isaf27, and KAN for reviewing our problems and being great coordinators!

Huge thanks to the following users for testing our round: kefaa2, AmShZ, dorijanlendvaj, Keshi, czhang2718, 2020akadaver, Magikarp1, Richw818, quantum8, RayLee234, I_Love_YrNameCouldBeHere, Qualified, 1-gon, smax, m371, kassutta, namanbansal013, HackerMonk, Ari, PurpleCrayon, FieryPhoenix, Jellyman102, bWayne, Omkar, Aleks5d, Makcum888

And as usual, thanks to MikeMirzayanov for the great Codeforces and Polygon platforms.

You will have 2 hours and 15 minutes to solve 9 problems. The score distribution will be announced very shortly before the contest starts. Good luck to all!

UPD1:

Score distribution: $$$500$$$ — $$$1000$$$ — $$$1500$$$ — $$$1750$$$ — $$$2250$$$ — $$$2750$$$ — $$$3000$$$ — $$$3500$$$ — $$$4000$$$.

UPD2:

Thanks to everyone who participated in the contest! We hope you enjoyed the problems. We apologize for the issues at the beginning of the contest; we hope that you were still able to have a great experience.

Editorial

UPD3:

Congratulations to the winners of Codeforces Round #749 (Div. 1 + Div. 2, based on Technocup 2022 Elimination Round 1)!

1. medium_waxberry
2. fivedemands
3. jiangly
4. peti1234
5. xay5421
6. Um_nik
7. orzdevinwang
8. yosupo
9. SHZhang2
10. tatyam

And a special congratulations to peti1234 for being the only contestant to solve problem I!

Congratulations also to the winners of Technocup 2022 - Elimination Round 1!

1. Ormlis
2. SomethingNew
3. Arayi
4. alexxela12345
5. I_HATE_CONSTRUCTIVES
6. oleh1421
7. Mangooste
8. arbuzick
9. idontwannawin
10. Dasha_Gnedko

Hello, Codeforces.

Please, welcome c++20 support on Codeforces. Yes, it is 64-bit. Thanks to Brecht Sanders: I used his distribution GCC-11.2.0-64 from https://winlibs.com/.

If you have installed PBOX, you can add this compiler with the line pbox install gcc11-64-winlibs. Probably, a good idea is to add C:\Programs\gcc11-64-winlibs\bin into the PATH. More about PBOX you can read here.

I use the compilation command line similar to other GCC installations: g++ -Wall -Wextra -Wconversion -static -DONLINE_JUDGE -Wl,--stack=268435456 -O2 -std=c++20 <source>. The only differences are -std=c++20 and -Wall -Wextra -Wconversion (I plan to use somehow such warnings in Polygon to suggest fixes in uploaded files).

Now you can use c++20 in your solutions. I'm not sure there are many features useful in competitive programming. Probably, I'm wrong. For example, now you can write vector v{vector{1, 2}}; instead of vector<vector<int>> v{vector<int>{1, 2}};. What else is useful? Please, if you are good with modern C++ then write.

You might be interested in looking at such a table. Before implementation, I always test every C++ distribution for the efficiency of reading and writing large amounts of data. For example, the latest GCC compiler from MSYS2 is terribly slow in some cases. I don't want to use it here. Also, it happens that some specifiers like lld or Lf work unexpectedly. In the table by reference, the second line is the added compiler. The columns correspond to different tests. The cell contains the time of the test execution. If I have time, I will someday publish scripts for testing c++ compiler installations.

Bye for now,
— Mike

Hello, Codeforces!

I'm glad to invite you to amazing (we've tried to make it such) Codeforces Round #748 (Div. 3) which will start on Oct/13/2021 17:35 (Moscow time). This round is made by me (MrPaul_TUser), a significant contribution to the round was also made by MikeMirzayanov and BledDest.

The round contains 6-8 problems. The difficulties of the problems are expected to compose an interesting competition for participants with ratings up to 1600. However, all of you who wish to take part and have a 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. We tried to make really strong tests — just like you will be surprised if many solutions fail after the contest is over.

You will be given 6-8 problems and 2 hours 15 minutes 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 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 _c_k_r_, Vladosiya, spotless, Yousry, powergee101, ncduy0303, I_Remember_Olya_ashmelev, A_Killer, OlegZubkov, mahade31, arjunsanjeev7, and UpS0lver for testing the round and improving tasks.

Good luck and have fun!

UPD Editorial

Hello Codeforces!

On Oct/10/2021 12:05 (Moscow time) Educational Codeforces Round 115 (Rated for Div. 2) will start. Note that the start time is unusual.

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 Alex fcspartakm Frolov, Mikhail awoo Piklyaev, Max 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:

Hello once again, Codeforces!

We are thrilled to congratulate our faculty member Nikolay KAN Kalinin on his first place at the ICPC World Finals, celebrated in Moscow, Russia. Years of training by Nikolai and his team from Nizhny Novgorod State University lead them to the top of the scoreboard, defeating teams from 116 other universities and becoming world champions.

We would also like to congratulate our future student Egor kefaa2 Dubovik, who won the silver medal with the Belarusian State University. Egor will join our Masters in Computer Science in the coming weeks.

We are looking forward to seeing Nikolay again next January when he teaches his course on Advanced Algorithms and Data Structures alongside Mike Mirzayanov. In this course, students focus on key and in-depth algorithms and data structures that form a modern computer specialist’s toolkit.

We are always excited to see Codeforces participants as our students here at Harbour.Space, so once again we’ve given a special discount (up to 70%) for the single course participation in Barcelona, Spain (travel cost and accommodation are not included).

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

Harbour.Space University

UPD: The editorial can be found here.

Hello, Codeforces!

Microsoft Development Center Serbia is thrilled to announce the finals of the 14th edition of Bubble Cup competition! Bubble Cup is an international, ICPC-style team contest aimed at university and high school students.

Contest will take place on Saturday, 9th of October at 10AM CEST, in online format. Winners will be announced at the closing ceremony. You can find more info on the BubbleCup website.

Just like the previous editions, this final will be followed by an online mirror competition on Codeforces. Mirror will take place on the same day about an hour after the start of the finals — Oct/09/2021 12:05 (Moscow time). Contest will last for 4 hours and ICPC rules will be applied. It will be a competition for teams of 1-3 members. There will be at least eight problems.

Just like last year, the finals are divided in two "divisions", called Premier League and Rising Stars. The two contests will have most of their problems in common, but the Rising Stars competition will feature some easier tasks targeted at high school contestants.

Both of the contests will be mirrored here on Codeforces, with Premier League mapping to the Div1 contest and Rising Stars mapping to the Div2 contest. The mirror will use native Codeforces ICPC team contest rules. Each team is allowed to use multiple computers.

Both contests will be unrated, due to the format and the length of the mirror being dissimilar to the standard Codeforces rated rounds.

The problems and their solutions were created by employees and interns of Microsoft Development Center Serbia: niksmiljkovic, acac97, renea, BubbleCup, nikolapesic2802, berke00, davidmilicevic97, ijevtic, dj0l3, igzi, Kole, Vasiljko, pavlej and me TadijaSebez.

We give our thanks to Nikolay Kalinin (KAN) and Mike Mirzayanov (MikeMirzayanov) for making these mirror contests possible and for the wonderful Codeforces and Polygon platforms. Special thanks goes to Alexandr Lyashko (knightL) for helping out with problem testing.

You can find problems from previous finals on our Codeforces online mirror competitions:

Bubble Cup 8 — Finals [Online Mirror]

Bubble Cup 9 — Finals [Online Mirror]

Bubble Cup X — Finals [Online Mirror]

Bubble Cup 11 — Finals [Online Mirror, Div. 1]

Bubble Cup 11 — Finals [Online Mirror, Div. 2]

Bubble Cup 12 — Finals [Online Mirror, Div. 1]

Bubble Cup 12 — Finals [Online Mirror, Div. 2]

Bubble Cup 13 — Finals [Online Mirror, Div. 1]

Bubble Cup 13 — Finals [Online Mirror, Div. 2]

We wish good luck to all participants!

UPD: Editorial

Hello, Codeforces!

Welcome to the ICPC Communication Routing Challenge powered by Huawei!

This challenge edition is very special, as it will be happening in conjunction with the ICPC World Finals! For those who are not participating in the finals — ICPC and Codeforces are offering a unique chance to compete during a 5-day Challenge Marathon and win amazing prizes from Huawei!

ICPC Challenge Marathon (open to public, unrated): October 9-14, 2021, 00:00 UTC:

This time we’re delighted to provide you with a future-oriented topic – routing algorithms for next-generation communication. During this Challenge we will provide you with a super-large inter-satellite optical network to properly plan message paths, to reduce communication latency and improve resource utilization. However, finding the optimal path in a network with limited resources is an NP-hard problem. Considering the physical constraints of optics and circuits, our algorithm faces greater technical challenges:

• How can we model and abstract device constraints and design algorithms in the most appropriate way?
• Is there an algorithm that takes almost the same time to calculate routes as the network scale increases?
• Is there any way to obtain the theoretical optimal solution in a short period for ultra-large networks?

We hope that these satellite communications challenge questions can help you understand the problems that Huawei's software algorithm researchers face every day. All the best!!!

Prizes

For 3-hours onsite ICPC World Finals Challenge Huawei will provide prizes to the winners in 2 groups of participants:

• Group 1: TOP 30 ICPC World Finalists, who participate individually:

  1st-10th place	HUAWEI MATE 40 Pro
  11th-20th place	HUAWEI MatePad Pro
  21st-30th place	HUAWEI WATCH 3 Pro

• Group 2: TOP 9 ICPC World Finals Coaches and Co-Coaches, who participate individually:

  1st-3rd place	HUAWEI MATE 40 Pro
  4th-6th place	HUAWEI MatePad Pro
  7th-9th place	HUAWEI WATCH 3 Pro

For 5 days online Challenge Marathon, Huawei will provide prizes to TOP 30 individual participants:

* The 1st place winner will get additional bonus in amount of 5000 USD. If the bonus cannot be transferred to the winner due to any reason, it may be replaced by a prize of the same value.

If the allocated Huawei Challenge prize cannot be delivered to your region for any reason it may be replaced by another prize of the same value (if no legal restrictions), at the discretion of the sponsor.

By participating in this Challenge, you agree to the Challenge Rules and Conditions of Participation

Good luck to all participants!

UPD: The contest duration has been extended to 5 days. The actual finish time is October 14, 2021, 00:00 UTC