I am the coordinator of Round #810. I will be brief and clear.

The div1E problem was copied by one of the two authors, it was not a coincidence.

For this reason, the div1 part of the round is unrated. Div2 stays rated.

Sometimes known problems appear in a contest, it happened to me as an author and to any problem setter who has organized many contests. This is never a reason to make a round unrated. Today something different happened, the problem was deliberately copied and the author did not tell anything to anybody (not even to the other author). Codeforces (and me personally) condemns this behavior.

A final personal remark: I feel sad. Please future authors: do not copy problems. It's a waste of everyone's time.

Hello Codeforces!

We are glad to invite you to our Codeforces Round Codeforces Round 810 (Div. 1) and Codeforces Round 810 (Div. 2) which will be held on 24.07.2022 17:35 (Московское время). This round will be rated for participants of both divisions. Participants in each division will be offered 5 problems and 2 hours to solve them. The two divisions will share 3 problems.

The problems are prepared by me and zxyoi. We hope that everyone will enjoy this round!

We are sincerely thankful for the help provided by:

• dario2994 for his marvelous coordination of this round,

• wyyxhjth for providing feedback on our early ideas,

• flukehn,FairyWinx,Pinkyhead,Vladithur,naman1601,dorijanlendvaj,c337134154,STommydx,LeoRiether,hxu10,Warriors_fsy,idxcalcal,jiaangk_,yakamoto,kiwiHM,Joyemang,forxen for testing our round and giving detailed feedback,

• FairyWinx for finding that one of our problems is coincident with a well-known problem (We replaced it),

• Vladithur for polishing our statements,

• KAN for his great help to our round,

• MikeMirzayanov for the amazing Codeforces and Polygon platforms!

We tried our best to have detailed, clear, and short statements. I think that anyone can find some interesting problems in this contest. We suggest to read all the statements.

The score distribution will be announced later.

Wish you good luck and high rating!

UPD

For some reason, we have removed one of our problems. So now participants in each division will be offered 5 problems and 2 hours to solve them.

The score distribution is:

Div2: $$$500-1000-1500-2000-3000$$$

Div1: $$$500-1000-1750-2000-2750$$$

We have some more testers now, let's thank them!

UPD2

We adjusted our score distribution slightly.

UPD3: the Div. 1 part of the round is declared unrated.

UPD4

Sorry for the late editorial.

UPD5

Congratulate to winners:

Div1

1. nantf

2. ko_osaga

3. Rebelz

4. The_Noble_Brahman_Bison

5. VivaciousAubergine

Div2

1. csyakuoi

2. Linkus

3. yaoxi

4. RGB_ICPC1

5. bajablast

Hi. I'm organizing an online IOI-preparation camp in collaboration with Huawei. Every day will be a 5-hour virtual contest, then my problem analysis, and sometimes a lecture. There will be at least 4 contests and 2 lectures.

We will do some old IOI contests (2013?) from the IOI archive, CEOI (2015-2016?), or maybe JOI/JOISC — to be decided this weekend. I don't want to do recent years like 2021 because most participants already covered it. The example lecture topics are those from Range Queries or Trees in Usaco Guide Platinum.

The camp is free for IOI 2022 participants. For everybody else, the video recordings will be posted on Youtube after the camp. By participating you get the live experience (Discord, asking questions, competing with others, leaderboards).

Dates: 25.07-2.08 (updated)
Time of every analysis/lecture: 14:00 UTC / 16:00 CEST
Price: free for IOI participants, 40 USD for everybody else
Platform: Discord & Codeforces & uj.oz (?)

Big thanks to Huawei UK R&D for sponsoring this camp.

EDIT: I'm now aware of CEOI collision. There's nothing I can do about it :(

Schedule:
25.07 — CEOI 2016 day 1
26.07 — CEOI 2022 day 1 + lecture
27.07 — CEOI 2016 day 2
28.07 — CEOI 2022 day 2
29.07 — lecture + homework
weekend off
1.08 — CEOI 2017 day 1
2.08 — CEOI 2017 day 2

Participants voted to cover CEOI instead of IOI to avoid problems that they already know.

Hello Codeforces!

On Jul/21/2022 17:35 (Moscow time) Educational Codeforces Round 132 (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 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:

WORK & STUDY OPPORTUNITY IN BANGKOK — B.GRIMM POWER x HARBOUR.SPACE UNIVERSITY

B.GRIMM POWER has partnered with Harbour.Space University to offer Bachelor's and Master’s degree scholarships in Data Science as well as work experience in one of the main infrastructure developers in Thailand.

B.Grimm Power PCL (B.Grimm Power), is a Thailand-based electricity generating and distribution energy company. B.Grimm Power is involved in the development, financing, construction and operation of power plants. Its product portfolio includes solar, hydro, wind power, and Diesel.

We are looking for various junior to mid-level candidates to work on solving tasks in the following fields:

• Data analysis
• System integration
• AI
• Forecasting Modeling

All successful applicants will be eligible for a 100% tuition fee scholarship (22.900 €/year) provided by the B.GRIMM POWER.

CANDIDATE’S COMMITMENT

Study Commitment: 3 hours/day ‍

You will complete 15 modules (each three weeks long) in one year. The daily class workload is 3 hours, plus homework to complete in your own time.

Work Commitment: 4+ hours/day ‍

Immerse yourself in the professional world during your apprenticeship. You’ll learn from the best and get to apply your newly acquired knowledge in the field from day one.

REQUIREMENTS:

• Industry experience
• International exposure
• Eager to learn
• Entrepreneurial mindset
• (Thai Language is a plus, not a must)

UPD: Editorial is out

Hi Codeforces,

We're excited to invite you to Codeforces Round 809 (Div. 2), which will take place at Jul/18/2022 17:35 (Moscow time). All problems were created and prepared by lunchbox, lce4113, and me. It will be rated for all participants with ratings lower than 2100.

Thanks to the people that made this round possible:

• IgorI for coordinating the round, patiently guiding us through the preparation process, and translating all statements to Russian.
• KAN, for guiding and assisting IgorI in the coordination.
• Apple_Method, izhang, lethan3, moo., null_awe, and ezraft for proposing problems that didn't make it to the final version of the round.
• PurpleCrayon for feedback and suggestions in the early stages of the round.
• Our testers, for their time and feedback: EnDeRBeaT, Queue, AlperenT, FairyWinx, ak2006, TheScrasse, sus, SirPh, litesam, asrinivasan007, Igorbunov, Runtime-Terr0r, timreizin, and Aaeria.
• MikeMirzayanov for the excellent platforms Codeforces and Polygon.

You will be given 2 hours to solve 5 problems, one of which will be divided into 2 subtasks. The scoring distribution will be announced later.

UPD: The scoring distribution will be $$$500 - 1000 - 1250 - (1000 + 1250) - 2250$$$.

UPD2: The editorial has been posted at https://codeforces.com/blog/entry/105008.

UPD3: Winners

Official

1. WYZFL
2. c8k
3. tiger1926
4. b6e0
5. iztrax

Everyone

1. tourist
2. SSRS_
3. WYZFL
4. Rubikun
5. noimi

Hello, Codeforces!

Imakf and I are glad to invite you to Codeforces Round #808 (Div. 1) and Codeforces Round #808 (Div. 2), which will take place on Jul/16/2022 17:35 (Moscow time). In both divisions, you will be given 6 problems and 2 hours to solve them all.

We would like to thank:

• Monogon for his 1-year cute coordination and very helpful discussion.
• KAN for the great help with round preparation.
• Wolam for his discussing the problems with us, which helps us to find the solution.
• smg23333 for donating his csgo time to test the problems in advance.
• AliShahali1382, SecondThread, wxhtzdy, taran_1407, Retired_cherry, antontrygubO_o, Tlatoani, errorgorn, hg333, kassutta, timreizin, Taday, Qiulyqwq, dorijanlendvaj, arvindr9, gamegame, EmptySoulist, prabowo, Yakumo_Ran, star_xingchen_c, generic_placeholder_name, 74TrAkToR and Ari for testing the round and their invaluable feedbacks.
• MikeMirzayanov for amazing platform Codeforces and Polygon.
• geranazavr555, KAN, myav and unreal.eugene for translating the statements into Russian.

Score distribution will be announced before the round.

Wish you all wouldn't gain negative ratings in this round! (This is theoretically possible XD)

UPD1: Score distribution is

Div 2: $$$500 - 1000 - 1500 - 1750 - 2250 - 3000$$$

Div 1: $$$500 - 750 - 1250 - 1750 - 2500 - 3250$$$

UPD2: Editorial

UPD3: Congratulations to the winners!

Div 1

1. Isonan
2. djq_cpp
3. tourist
4. jiangly
5. Um_nik

Div. 2

1. _WidowMaker_
2. N193r
3. Ayaka_s_Dog
4. PaiGuChicken
5. NothingOccurred

Hello Codeforces,

We are glad to invite you to Codeforces Round 807 (Div. 2), which will be held on Jul/15/2022 16:35 (Moscow time). As usual, the round will be rated for participants with ratings lower than 2100, while those who have higher ratings are encouraged to participate unofficially. Please note the unusual start time.

You will be given 6 problems to be solved in 2 hours and 15 minutes. There may or may not be interactive problems, so you are encouraged to prepare in case they do appear by reading this guide.

The round is authored by abc241 and me, while joining us is also inwbearX who contributed significantly to the preparation. This is our first time setting rounds in Codeforces, and it wouldn't be possible if there were no support from the following people.

• errorgorn for fantastic coordination.
• KAN, mtw, geranazavr555, unreal.eugene and MikeMirzayanov for translating the statements into Russian.
• antontrygubO_o, kevinxiehk, mango_lassi, Adam_GS, mtw, Utkarsh.25dec, yz_, thanhchauns2, TLP.39, 36champ, jampm, DeMen100ns, Neothehero, and somerandomaltacc3034 for testing the round.
• MikeMirzayanov for Polygon and Codeforces.

The score distribution is $$$500$$$ — $$$1000$$$ — $$$1250$$$ — $$$1750$$$ — $$$2500$$$ — $$$3000$$$.

We are looking forward to your participation. Good luck and enjoy our round!

Update: the editorial is up!

Update 2: Winners!

Div. 2

1. stemroot
2. UtopianZ
3. WYZFL
4. H_stove
5. myeeye

Div. 1 + Div. 2

1. tourist
2. SSRS_
3. stemroot
4. Um_nik
5. arvindf232

Hello Codeforces!

SlavicG, flamestorm, MikeMirzayanov and I want to invite you to Codeforces Round 806 (Div. 4).

It starts on Jul/12/2022 17:35 (Moscow time).

The format of the event will be identical to Div. 3 rounds:

• 5-8 tasks;
• ICPC rules with a penalty of 10 minutes for an incorrect submission;
• 12-hour phase of open hacks after the end of the round (hacks do not give additional points)
• after the end of the open hacking phase, all solutions will be tested on the updated set of tests, and the ratings recalculated
• by default, only "trusted" participants are shown in the results table (but the rating will be recalculated for all with initial ratings less than 1400 or you are an unrated participant/newcomer).

We urge participants whose rating is 1400+ not to register new accounts for the purpose of narcissism but to take part unofficially. Please do not spoil the contest for the official participants.

Only trusted participants of the fourth division will be included in the official standings table. This is a forced measure for combating unsporting behavior. To qualify as a trusted participant of the fourth division, you must:

• take part in at least five rated rounds (and solve at least one problem in each of them),
• do not have a point of 1400 or higher in the rating.

Regardless of whether you are a trusted participant of the fourth division or not, if your rating is less than 1400 (or you are a newcomer/unrated), then the round will be rated for you.

Many thanks to the testers: TimDee, Gheal, Max_Calincu, qwexd, _Vanilla_,sandry24, jampm, haochenkang, tibinyte, Etherite.

We suggest reading all of the problems and hope you will find them interesting!

Good Luck!

Update: Editorial

Hello! Codeforces Round 805 (Div. 3) will start at 10.07.2022 17:35 (Московское время). You will be offered 7-8 problems 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 a rating of 1600 or higher, can register for the round unofficially.

The round will be hosted by rules of educational rounds (extended ACM-ICPC). Thus, solutions will be judged on preliminary tests during the round, and after the round, it will be a 12-hour phase of open hacks.

You will be given 7-8 problems and 2 hours and 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 a trusted participant of the third division, you must:

• take part in at least five 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 our work. Problems have been created and written by ITMO University teams: MikeMirzayanov, MisterGu, myav, Vladosiya, Aris, senjougaharin and me Gol_D.

Also many thanks to turmax, ivanz, antonis.white, Ronnie007, okwedook, oversolver, Kavaliro, antoshkin, omikad, yorky, Jostic11, Ziware, Kniaz, andrey.starodubtsev, Spaggetti and aniervs for testing the contest and valuable feedback.

Good luck!

UPD: Editorial

Hello Codeforces!

On Jul/08/2022 17:35 (Moscow time) Educational Codeforces Round 131 (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 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!

Welcome to the 131st educational round hosted by Harbour.Space and Codeforces.

Quite exciting, isn’t it? Now it's time for you to dive deeper into the competitive programming world with the 10 days intensive Summer Camp organized by Harbour.Space and Leagues of Code.

Don’t forget about the discounts for participating in our Summer Camp. Every member of the Codeforces community gets a 30% discount for on-site participation or a 50% discount for online participation with promo-code CFLOC2022.

Our Summer Camp is a training program that will teach participants competitive programming. It will take place in Barcelona and online on July 18-29, both participation formats are available.

We are inviting students ages 10 to 24, interested in improving their skills or seeking intensive, high-level training prior to the IOI. Teachers in the camp will be ICPC World Final Silver medalist 244mhq, SWERC 2022 Winners MaksymOboznyi, ICPC World Final Champion pashka and others. Participants will be divided into classes based on their level and previous experience. Classes will be held in English.

Good luck with the round!

UPD: Editorial is out