Hello Codeforces!

On Oct/20/2022 17:35 (Moscow time) Educational Codeforces Round 138 (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!

UPD: Editorial is out

Hello Codeforces!

On Oct/17/2022 17:35 (Moscow time) Educational Codeforces Round 137 (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 Ivan BledDest Androsov, Alex fcspartakm Frolov and me. Also huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

The round is based on the Qualification stage of the Southern and Volga Russian Regional Contest. Thus, we kindly ask its participants to avoid participating in the round.

Good luck to all the participants!

UPD: Editorial is out

Hello! Codeforces Round 828 (Div. 3) will start at Oct/16/2022 17:35 (Moscow time). You will be offered 6-8 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 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 6-8 problems and 2 hours and 15 minutes to solve them.

Note that the penalty for the wrong submission in this round 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 my work, pashka for help with ideas for problems and for coordination of my work. Problems have been created and written by MikeMirzayanov, 74TrAkToR and pashka.

We would like to thank: Gornak40, meowcneil, Vladosiya, senjougaharin, efimovpaul, powergee101, tanus_era for testing the contest and valuable feedback. List of testers will be updated.

Good luck!

UPD: Editorial

Hello Codeforces!

On Oct/15/2022 17:35 (Moscow time) we will host Codeforces Global Round 23.

It is the fifth round of a 2022 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 2022:

• 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 2022 supported the global rounds initiative!

The problems were written and prepared by AmirrzwM, MohammadParsaElahimanesh and napstablook, AquaMoon, Cirno_9baka, mejiamejia, ChthollyNotaSeniorious, SSerxhs, TomiokapEace, SomethingNew, pakhomovee, rembocoder, SirShokoladina.

We would also like to thank:

• 74TrAkToR, for coordinating and helping a lot to make this round happen (and rejecting all of my problems).
• er888kh and Mp007mp for giving ideas for some problems.
• Our testers for testing and providing helpful feedbacks: er888kh, sinamhdv, SoheilE, DeadlyCritic, egfhdbfweryg123, gamegame, Kostroma, Endagorion, AndreySergunin, MELNIKOFF_OLEG, zemen, iwalainz, halin.george, -skyline-, mejiamejia, triple__a, TomiokapEace, SomethingNew, efimovpaul, Rhodoks, meowcneil, plagues, Milesian, blobugh, SSerxhs, apeiya, E404_Not_Found, RUSH_D_CAT, willy108, _Veritas, oolimry, aaaaawa and Ynoi.
• MikeMirzayanov for creating great platforms Codeforces and Polygon.

Round Information:

• Duration: 2 hours and 15 minutes
• Number of problems: 7 problems and 1 sub task
• Score distribution: 500-1000-1000-1500-(2000+1750)-2500-3500
• There is an interactive problem, so please see the guide of interactive problems if you are not familiar with it.

We have tried our best to write clear problem statements and make strong pretests and we are looking forward to your participation!

UPD: Editorial

Hello Codeforces!

mesanu, flamestorm, MikeMirzayanov and I are glad to invite you to Codeforces Round 827 (Div. 4)! It starts on Oct/13/2022 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.

We would like to thank:

• pashka, keta_tsimakuridze, Gheal, AlperenT, KrowSavcik, Sho, badlad, qwexd, Phantom_Performer, haochenkang, _Vanilla_, sandry24, jampm, tibinyte for testing and great feedback!

• TimDee for helping with russian translations!

• badlad for helping with a problem!

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

GLHF!

UPD: Editorial

Hello! Codeforces Round 826 (Div. 3) will start at Oct/11/2022 17:35 (Moscow time). You will be offered 6-8 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 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 6-8 problems and 2 hours and 15 minutes to solve them.

Note that the penalty for the wrong submission in this round 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 team: MikeMirzayanov, myav, Gol_D, Aris, Gornak40, senjougaharin and Vladosiya.

We would like to thank: Mangooste, Ormlis, oversolver, Be_dos, IzhtskiyTimofey, Stefan2417, ace5, BledDest, AbsurdMan, toxabuk, Kniaz, goncharovmike, YTatarin, pashka and great_fortune for testing the contest and valuable feedback. List of testers will be updated.

Good luck!

UPD: Editorial

Hello, Codeforces!

mtw, naman1601 and I are glad to invite everyone to participate in Codeforces Round 825 (Div. 2), which will be held on Oct/10/2022 17:35 (Moscow time).

This Round will be rated for participants with rating lower than 2100.

You will be given 5 problems with one subtask and 2 hours to solve them

We would like to thank:

• Arpa for coordinating the round.
• KAN for help in preparation of the round.
• Everule for proposing a task that did not make it to the final problemset.
• BucketPotato, PurpleCrayon, the_hyp0cr1t3, welleyth, MagentaCobra, recurecurring, GoatTamer, udhavvarma03, 74TrAkToR, AwakeAnay, valeriu, TheScrasse, kal013, avi0000, Perpetually_Purple, codemastercpp, CoderAnshu, IceKnight1093, Dio707, hsekharsahoo, tibinyte, Vladithur, master._.mind, mejiamejia, zalak_b, Non-origination, SlavicG, manish.17, dedsec_29, Mo2men and nor for testing this round and providing feedback.
• MikeMirzayanov for great Codeforces and Polygon platforms.

The score distribution will be announced closer to the start of the round.

UPD1: Score distribution is 500 — 1000 — ( 1250 + 2000 ) — 2000 — 2500.

UPD2: Congratulations to the winners!

Overall:

• noimi
• LJC00118
• tute7627
• kotatsugame
• Nephren--Ruq--Insania

Rated:

• Nephren--Ruq--Insania
• dongzhuo
• Kurorz
• wildfire032
• _gxyd

UPD3: Editorial is out.

Good luck and have fun!

Hello Codeforces. Hoping you're having a wonderful day! ^_^

DYTECHLAB Cup 2022

This October, we invite you to the first ever Dytechlab Cup 2022 that will start on Oct/07/2022 17:35 (Moscow time). The problems were prepared by members of our company who share a passion for Competitive Programming. It is an open and rated round for both divisions.

The round will consist of 7 problems and will be 150 minutes long. We wish everyone good luck and have a positive delta!

Prizes

• 1st place: US$200 cash prize
• 2nd place: US$100 cash prize
• 3rd place: US$50 cash prize

Also, we understand that contestants like dope MERCHANDISE, so we are giving away lots of them!

• Top 20 will get a merchandise package which will include: a t-shirt with your Codeforces handle on it, a notebook, 2 pens, and a sports bag.
• 30 merchandise packages, each including a t-shirt & 2 pens will be randomly distributed to 30 contestants ranking 21-200.
• 100 merchandise packages, each including a sports bag & 2 pens will be randomly distributed to 100 contestants ranking 201-1500.

All packages will include stickers in it, so you can stick them to your laptop and show your friends how hardworking you've been :p

Our appreciation goes to

• MikeMirzayanov for the Codeforces and the Polygon platform.
• gop2024 for coordination of the round.
• magnified for one of the problems and your enthusiastic support in preparing the round.
• blobugh for one problem that fills in the gap to finalize the contest.
• ngfam_kongu, MofK, ladpro98 and every other Dynamic Technology Lab member who helped in coordination, was spot-on while we were working together in the office and helped me come up with ideas for problems.
• The list of testers (still updating): KAN, Elite_Vanor, HmmOrange, Kuroni, .DucAnh., LetterC67, nguyentien_zzz, VanIOImaster153, ngd.nam, nigus, hank55663, VuaVeNhi, lobotomy, kieusontungcva, ehnryx, stevenkplus, MagentaCobra, dorijanlendvaj, djq_cpp, ugly2333, gyh20, TomiokapEace, SSerxhs, jeroenodb, willy108, abc864197532, -skyline-, blobugh, ak2006, satyam343, Andreasyan, emorgan.

Wish you the best and a very positive delta in this round!

UPD: score distribution is: $$$500 - 1000 - 1500 - 2000 - 2750 - 3500 - 3750$$$.

UPD2: Scripts to generate ranks of random prize winners. Seed $$$x$$$ will be the sum of score of the top 10 participants:

./genrandom_winners x

#include "testlib.h"
#include <bits/stdc++.h>
using namespace std;

/*
*  rnd.next(4) - Random int bw 0-3
*  rnd.next(4, 100) - Random int bw 4-100
*  rnd.next(10.0) - Random real [0;10)
*  rnd.next("one|two|three") Random word out of 'one', 'two' and 'three'
*  rnd.next("[1-9][0-9]{99}") Random REGEX (100-digit number as a string)
*  rnd.wnext(4,t) wnext is a method of obtaining an uneven distribution (with a biased expectation)
*  rnd.any(container) A random element of the container container (with random access via an iterator), for example, it works for std::vector and std::string
*  shuffle
*/

int main(int argc, char* argv[])
{
  registerGen(argc, argv, 0);
  vector <int> shirt_winners = {};
  vector <int> bag_winners = {};

  for (int i = 21; i <= 200; i++) shirt_winners.push_back(i);
  for (int i = 201; i <= 1500; i++) bag_winners.push_back(i);

  shuffle(shirt_winners.begin(), shirt_winners.end());
  shuffle(bag_winners.begin(), bag_winners.end());

  // list of shirt winners
  cout << "===== Rank of SHIRT WINNERS =====\n";
  for (int i = 0; i < 30; i++) {
    cout << shirt_winners[i] << ' ';
  }
  cout << "\n";

  // list of bag winners
  cout << "===== Rank of BAG WINNERS =====\n";
  for (int i = 0; i < 100; i++) {
    cout << bag_winners[i] << ' ';
  }
  cout << "\n";
}

UPD3: Editorial.

The total score of top 10 is: $$$11460 + 9086 + 8829 + 8609 + 8380 + 8354 + 7511 + 6874 + 6775 + 6755 = 82633$$$. The list of ranks of prize winners is fixed and you can check using the published code above, using the total above as a seed. I will make a list the following days and contact the prizes winners! PLEASE NOTE that the list of real winners only finalized after the system detect & remove cheaters!

Congratulations to everyone and HAVE A GOOD WEEKEND!

UPD4: standings

Winners:

First to solve:

About Dytechlab & Job Opportunities

If you are interested in employment opportunities in Eastern Europe, Dubai, or South East Asia, please fill out the contact form below:

We are Dynamic Technology Lab, Pte Ltd. (DTL), a quantitative hedge fund engaging in global securities trading with multiple asset classes. Since our founding in 2009, from humble beginnings in a home garage, we are now a sizable, well-established financial institution with offices in Singapore, Shanghai, Beijing, and Hanoi. Our success is fueled by some of the most inquisitive minds who are relentless in their pursuit of innovation.

As a tech-focused Licensed Fund Management Company under the Monetary Authority of Singapore, DTL is dedicated to producing strong consistent returns for its investors by relying on mathematical and statistical models to drive its investment process.

Right now, we are looking for lots and lots of Engineering positions and are ready to bring opportunities to work in a quantitative trading environment for Engineers of all levels, all around the world!

Learn more about us on this blog or on our website!

Hi, Codeforces!

Three years later, first ideas of a contest turned into this complete set of problems, so I am glad to invite you to take part in Codeforces Round #824 (Div. 2), which will take place on Oct/02/2022 17:35 (Moscow time). The round will be rated for the participants with rating lower than 2100. Participants from the first division are also welcomed to take part out of competition.

You will be given 2 hours 15 minutes to solve 6 problems. All the problems were created and prepared by me.

I would also like to thank:

• KAN for awesome coordination!
• Aleks5d, arzhantsev64, ChthollyNotaSeniorious, DanWallgun, MagicalFlower, Gegege337, Imakf, LeoRiether, mejiamejia, okwedook, PO3OBAR_Bblnb, SSerxhs, TomiokapEace, triple__a, wabadabakalakaboo for testing the round and giving significant feedback.
• mejiamejia for his help with extra testing.
• MikeMirzayanov, geranazavr555, unreal.eugene, DK318, and KAN for maintaining Codeforces and Polygon platforms!

Scoring: $$$500-750-1250-1750-2250-3000$$$.

Note that some problems have similar scores. Your sense of the scoring distribution may differ, don't forget to read further problems if you get stuck.

I look forward to seeing you on the leaderboard. I hope you'll enjoy all 6 problems and wish you good luck!

UPD1: Editorial

UPD2:: Winners and First to solve

Div2

Div1 + Div2

First to solve