Hello, Codeforces!

We are happy to invite you to our experimental round for three divisions, which will take place at Oct/22/2023 14:05 (Moscow time). Please note the non-standard start time for the round. Each division will have 5-7 tasks. The round will be held according to the Codeforces rules and will be rated for all three divisions. A few changes regarding the ratings of participants in this competition:

• In Div.3 the rating of participants is less than 1600.
• In the Div.2 ranking, participants range from 1600 to 2099.
• In Div.1 the rating of participants is no less than 2100.
• Please note that after Codeforces Round 904 (Div. 2) the rating will not be recalculated until the end of this competition.

Let us note that two team Olympiads will be held in parallel on this day and the rounds are based on their tasks:

• XXI Moscow Team Olympiad, high school students competition based in Moscow that is an elimination contest for All-Russian Team Olympiad.
• III Open Team Olympiad UMSh in programming.

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

• Coordinators Artyom123 и Vladosiya for excellent coordination and useful advice.
• Problem authors 74TrAkToR, Mangooste, TheEvilBird, Tikhon228, teraqqq, valerikk, Dmitry07.
• Testers pavlekn, zwezdinv, 1000--7, SashaT9, maks_simenkov, orolik, tmari_sun, OR_LOVe, MalkevichAS, TimVen74, _shakespeare_, myav, ctraxxd, Gassa, OAleksa, Acanikolic73, AndrewPav, AlphaMale06, NemanjaSo2005, dorijanlendvaj, defnotmee, meOwO, Yuu, CIXTEEN, golions, MagentaCobra, FairyWinx, v0s7er, adepteXiao, induk_v_tsiane, Alexdat2000, Be_dos, mr.kolya, kevinxiehk, alexxela12345, talant, Allvik06 for high-quality testing!
• MikeMirzayanov for amazing Codeforces and Polygon platforms.

We wish you good luck and high rating!

UPD: One of the problems will be interactive, so please read guide for interactive problems before the contest.

UPD: Score distribution:

• Div.3: $$$500-1000-1500-1750-2500-2750-(1750+2000)$$$
• Div.2: $$$250-500-1000-(750+1250)-2250-2750$$$
• Div.1: $$$(250+500)-750-1000-1250-2000-2750$$$

UPD: Editorial

UPD: We will retest the solutions to the problem div3F and div2C. This may make minor changes, the rating will be recalculated later.

UPD: Retesting took several minutes. Now all the results are correct :)

Hello, Codeforces!

I am happy to invite you to my Codeforces Round 904 (Div. 2) which will be held at Oct/22/2023 10:05 (Moscow time). The round will be rated for all the participants with rating strictly less than 2100.

The tasks were created and prepared by 74TrAkToR. I would like to thank everyone who helped me a lot with round preparation.

• Coordinator irkstepanov for excellent communication and help with preparation.
• Testers Golovanov399, tibinyte, Silver_Fox, Illumina, eeeDA, coder8080, valeriu, XaRDKoDblCH, cristi_tanase, pshat, Vladosiya, DIvanCode, nnv-nick, priyanshu.p for high-quality testing and valuable advices.
• AlFlen for the idea of one of the tasks and two wonderful years together!
• All members of the jury of the team Olympiad CheReKoSH, because the round is made up of the tasks of this Olympiad.
• MikeMirzayanov for amazing Codeforces and Polygon platforms

During the round you will need to solve 5 problems. You will have 2 hours to solve them.

Score distribution: $$$500-1000-1750-2500-3000$$$

We wish you good luck and high rating!

UPD: Editorial

Hello, Codeforces. Friends.

I apologize, but today I will be a bit chaotic and mix personal with public. It just happened that way, I'm sorry.

Today, my mother passed away. It's hard for me to write this. Even just seeing it in text makes it feel like something from a nightmare.

She was extraordinary. It's difficult for me to articulate it right now, but take my word for it. It felt like all the best qualities one could imagine in a mother converged in her. I don't know any other people so kind, sincere, non-judgmental, capable of love, listening, befriending, supporting, and taking joy in the world around them, and bringing joy to their loved ones. Mom, it's already hard without you, it feels empty.

She had glioblastoma. It's an aggressive brain cancer that affects only a few people out of 100,000. I believe, I hope, that science will soon be able to tackle this disease. But for now, this diagnosis is a death sentence. Maybe some of you are or will be associated with medicine. I want to say thank you, I hug you.

Perhaps this is some form of catharsis, but visiting the Codeforces pages today, I pondered why I do this. What am I seeking here?

I want to enter another world. A world free from the insoluble problems of human ambition. A world where we discuss problems, algorithms, and programming.

The world is unjust and restless. It has black, white, blood-red, and some gray shades of unclear tones. But here, on Codeforces, I'm not looking for answers to all questions. I hug all of you and wish you peace, tranquility, and joy.

You may perceive this as a whim of mine, but now I don't want to see topics here that are considerably broader than programming, mathematics, and life outside our competitions. I want a united community, an intellectual oasis.

Focus on our competitions, not on global issues, will help me personally continue to be engaged in the community, develop and move it forward.

Please refrain from making posts, comments, or any other forms of expression on contentious topics like national/ethnic conflicts, politics, religion, sexual orientation, and gender identity, and any other topics distant from programming competitions that might lead to disputes or conflicts. We won't solve these problems here, we just can't.

Give me some time, and I will likely hide the most contentious posts on these topics. Please refrain from publishing anything that is beyond or close to the boundary mentioned above. By publishing materials that contain signs of such discussions, be prepared for read-only mode and other administrative measures.

I realize that I'm now limiting Codeforces and diminishing the community's involvement in our lives. But this is how I feel today, and I ask for your understanding. I wish you peace and love.

M.

P.S. Please cherish your loved ones while they are with you. Give them your attention. Bring joy to them, love them.

UPD 1: Friends, thank you very much for your attention. I read all the comments and am grateful to everyone who supported me.

UPD 2: Yesterday the funeral took place. Thank you for your support. With your help, it's easier for me to get through all of this.

Hello, Codeforces!

I, ChurakovaAlexandra, and medvezhonokok are students of ITMO, and since this August, we started our internship at Codeforces. We are delighted that now we have the opportunity not only to write academic code but to do something that competitive programming enthusiasts from all over the world use.

Currently, we are working on minor improvements to Polygon — a system for preparing problems. Later, as we gain more experience and delve into the technologies, we will also start working on Codeforces.

A big thank you to our mentors geranazavr555 and MikeMirzayanov, who are always there to help and support.

Here's a list of the main improvements to Polygon that we've made (sometimes with significant help from our mentors) over these two months.

Hello! Codeforces Round 903 (Div. 3) will start at Oct/12/2023 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 7 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.

Problems have been created and written by our team: myav, Gornak40, DmitriyOwlet and Vladosiya.

We would like to thank:

1. MikeMirzayanov for Polygon and Codeforces platforms.

2. SomethingNew, rniya, zwezdinv for red testing.

3. makrav, dbsic211, AlexanderL, KseniaShk, pavlekn for yellow testing.

4. gigabuffoon, EgorUlin, KerakTelor, Pa_sha, I_love_geom, petyb, MinaRagy06, toniskrijelj, FynjyBath for purple testing.

5. Abo_Samrah, dan_dolmatov, pedrosorio, ezdp, Illumina, Chrisedyong, Apachee, arseny2606 for blue testing.

6. t0rtik, Sergey140146659, hader239, Modern for cyan testing.

7. mkshh, petertromso for green testing.

Good luck!

UPD: Editorial

Hello Codeforces!

On Oct/09/2023 17:35 (Moscow time) Educational Codeforces Round 156 (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, Ivan BledDest Androsov, Maksim Neon Mescheryakov, Roman Roms Glazov, Alex fcspartakm Frolov and me. Also, huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Please note that the problems of this round partially intersect with the problems of the Qualification stage of the Southern and Volga Russian Regional Contest. If you took part in the qualification, please refrain from participating in the round.

Good luck to all the participants!

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

Scholarships for Master's students in Computer Science and Data Science are available in Harbour.Space University Barcelona campus!

Scholarship Summary:

• Fully funded scholarship (29.900 €/year) to study a Master’s degree in Data Science or Computer Science for two years
• Successful applicants will become part of the University’s “Talent pool” and will be shown to the sponsoring companies. In case the candidate is picked for the Work&Study Program from our industry partner, the student starts an internship with a commitment to study 3 hours/day and work for 4 hour/day

Please note preselected candidates will be requested to pay a non-refundable application fee of 85€ to study at Harbour.Space University.

Candidate’s commitment:

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.

Candidate’s requirements:

• Bachelor's degree in the field of Mathematics, Statistics, Data Science, Computer Science or similar
• English proficiency
• Advanced knowledge and experience in Python, SQL, Spark/Scala, and bash
• Experienced use of Big Data technologies: Spark, HDFS, Kafka, etc.
• Hands-on experience with Data Science techniques: feature engineering,
• Strong ML knowledge
• Strong Software Engineering Background
• Problem-solving aptitude

Note: These scholarships are only available for qualified applicants with a bachelor’s degree.

UPD: Editorial is out

Sugeng enjing, Codeforces! 🥰🥰🥰🥰

COMPFEST 15 is happy to invite you to participate in Codeforces Round 902 (Div. 1, based on COMPFEST 15 - Final Round) and Codeforces Round 902 (Div. 2, based on COMPFEST 15 - Final Round) on 08.10.2023 12:05 (Московское время). Both rounds will be rated. You will be given 2 hours and 30 minutes to solve 7 problems.

Note the unusual time of the round.

The problems are written by ArvinCiu, Pyqe, and nandonathaniel.

We would like to thank:

• KAN for helping to host the round;
• errorgorn and ScarletS for the based coordination;
• gansixeneh and nandonathaniel for helping with the problem preparation;
• ArvinCiu, CyberSleeper, and Edbert.H for providing alternate solutions in the early stages;
• Alexdat2000 for writing the Russian translations;
• Aaeria, AMnu, Berted, BucketPotato, buffering, Drew_, dorijanlendvaj, eggag32, Elben85, emorgan5289, faustaadp, ffao, fishy15, flamestorm, gamegame, hocky, Insta-x, jdurie, joelgun14, KerakTelor, Marky, Murinh0, nvmdava, nyab, Owmicron, prvocislo, PurpleCrayon, rama_pang, TakeMe, sahil_k, user202729_, Vladithur, WHCPP, and ZeroScar for testing the contest and providing us very useful feedback;
• Universitas Indonesia, all the local committees, administrators, and managers of the whole COMPFEST event;
• MikeMirzayanov for the amazing Codeforces and Polygon platform!

COMPFEST itself is an annual event hosted by Universitas Indonesia. It is the largest student-run IT event in Indonesia and competitive programming contest is one of the competitions hosted.

We hope you will enjoy and have fun in the contest. Muga-muga beja lan isa entuk biji apik!! 💪💪🔥🔥

UPD: Scoring distribution

• Div. 1: 500 — 1000 — 1250 — 1750 — 2250 — 2750 — 3250
• Div. 2: 500 — 1000 — 1500 — 2000 — 2500 — 2750 — 3000

UPD2: Contest is over!

Congratulations to our winners!

Congratulations for our first solvers:

We will try to post the editorials as soon as possible. Please stay tuned!

UPD3: Editorial

On behalf of the COMPFEST committees, we are glad that our Codeforces Round ran quite smoothly and we hope that you all enjoyed our problems. See you next year! 😍😍

Hello, Codeforces!

We've compiled a list of command lines that Codeforces uses to compile and run solutions in various languages and compilers.

It is up-to-date as of today (2023-10-06), and we will make efforts to keep it current in the future, but this is not guaranteed.

Hello, Codeforces!

I'm pleased to invite you to Codeforces Round 901 (Div. 1) and Codeforces Round 901 (Div. 2). It starts on Sep/30/2023 17:35 (Moscow time). It also means, the National Day of China arrives during the round. Wish you a nice vacation! 🎉🎉🎉

For both divisions, you will have 3 hours to solve 7 problems.

I would like to thank:

• errorgorn for his wonderful coordination.

• Alexdat2000 for Russian translation and Vladosiya for helping us with Russian clarifications.

• GeZhiyuan for providing all the problems and "a few" rejected problems.

• znstz2018 and SanweiTreap for helping me prepare the problems.

• Um_nik, wangziji, Heltion, Kevin114514 and flowerletter for Legendary Grandmaster Testing.

• sjcsjcsjc, He_Ren, GaryZ005, platelet, njwrz, thenymphsofdelphi, DerekFeng, Juanzhang and ttklwxx for International Grandmaster Testing.

• maomao90, juju527, zimpha, 765, xuanquang1999, CrTsIr and EasonTAO for Grandmaster Testing.

• SATSKY, lanhf, Hank2019 and Yakumo_Ran for Master Testing.

• DaniraSilla and kriepiekrollie for Candidate Master Testing.

• raulandreipop, micho, alwyn, ArgintLaAnu, IssamOtoz and jakao for Expert Testing.

• CLown1331 for Pupil Testing.

• You for participating the round.

• MikeMirzayanov for Codeforces and Polygon systems.

Especially, I would like to thank errorgorn for his great contribution to the round, njwrz for providing user solutions for all the problems, Kevin114514 for making the announcement and tutorial more readable.

Finally and most importantly, I would like to thank znstz2018 for helping me with everything patiently all the time. This round can't happen without him.

The main character of the problems will be Jellyfish, a sweet little girl. 🍏🍏🍏

Score distribution:

• Div.1: $$$500$$$ − $$$1250$$$ − $$$1500$$$ − $$$2250$$$ − $$$3000$$$ − $$$4000$$$ − $$$5000$$$

• Div.2: $$$500$$$ − $$$1000$$$ − $$$1000$$$ − $$$1250$$$ − $$$2000$$$ − $$$2250$$$ − $$$3000$$$

Good Luck & Have Fun! 🔥🔥🔥

UPD1: Editorial is out.

UPD2: Congratulations to the winners!