☀ ☀ ☀ Hey Codeforces ☀ ☀ ☀

Summer is ending, but my team and I are happy to invite you to participate in Codeforces Round 894 (Div. 3). The round will take place on Aug/24/2023 17:35 (Moscow time). You will be offered 7 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: diskoteka, pavlekn, playerr17. Ivang helped us with the idea of one of the tasks.

We would like to thank:

1. Vladosiya for coordinating the round

2. MikeMirzayanov for great Polygon and Codeforces platforms

3. feeder1, Xellos for red testing

4. michao, induk_v_tsiane, Phantom_Performer, vladmart, dmkz, LordVoIdebug, vrintle for yellow testing

5. kzyKT, celin for purple testing

6. segment_tea, Egorsa, MADE_IN_HEAVEN, Thost, BF_OF_Priety, mewnya, natalina, Serik2003 for blue testing

7. i_love_penguins, tnaito, akwa_blue, Zeyad_Hekal, NgJaBach for cyan testing

8. mkshh, myav for green testing

We wish you all good luck and a high rating!

UPD: Editorial published

Hello Codeforces!

On Aug/17/2023 17:35 (Moscow time) Educational Codeforces Round 153 (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 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:

Harbour.Space University has partnered with Giga (Unicef) to offer Master’s degree scholarships in the field of Computer Science and Front-end Development, as well as work experience.

We are looking for various junior to mid level candidates:

Front-end Developer:

This student will work closely with the blockchain developer and product lead to contribute to the design and implementation of user interfaces for the company's blockchain-based prototypes. They will be responsible for translating UI/UX design wireframes into functional and visually appealing web applications, ensuring seamless user experiences. The student will collaborate with blockchain and backend developers and designers to integrate front-end components with server-side logic and optimize application performance. They will also be involved in testing, debugging, and maintaining the front-end codebase. The intern will have the opportunity to gain practical experience in front-end development within the context of blockchain technology and contribute to the Giga’s mission of connecting schools to the internet.

• Solid understanding of HTML, CSS, and JavaScript
• Familiarity with front-end frameworks and tools such as React or Vue.js.
• Strong problem-solving skills, attention to detail, and a passion for creating intuitive user interfaces are essential

Full Stack Developer:

• Interest and experience in web application development, data products and OpenAPIs
• Comfortable with on-cloud deployment services (preferably Azure), Git and CI/CD pipeline and deployment processes
• Experience with open-source projects is highly preferred
• Strong ML knowledge
• Experience with data visualization tools like matplotlib, ggplot, d3.js, Tableau that help to visually encode data
• Excellent communication skills, — it is incredibily important to describe findings to a technical and non-technical audience
• Strong software engineering background
• Hands-on experience with data science tools
• Problem-solving aptitutde
• Analytical mind and great business sense
• Degree in computer science, engineering or relevant field is preferred

All successful applicants will be eligible for a 100% tuition fee scholarship (29.900 €/year) provided by the partner company.

CANDIDATE’S COMMITMENT

Study Commitment: 3 hours/day

You will complete 15 modules (each three weeks long) in one year. 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
• Sustainability is a key topic for you
• You want to work for an NGO

UPD: Editorial is out

Hello, Codeforces!

We are glad to invite everyone to participate in Codeforces Round 893 (Div. 2), which will be held on Aug/15/2023 17:35 (Moscow time).

Please note the unusual start time of the round. This round will be rated for the participants with rating lower than 2100.

Our round is completely set by SIS (Summer Informatics School) students. We did our best to prepare interesting and creative problems. You can check out some of the previous rounds prepared by SIS students: Codeforces Round 816 (Div. 2), Codeforces Round 815 (Div. 2),Codeforces Round #694,Codeforces Round #612,Codeforces Round #530.

Task authors and developers: Daria arbuzick Grekova, Petr green_gold_dog Losev, Yaroslav Kihihihi Semenyuk, Artem ArtAlex Alexeev, Anton NToneE Egorov, Fedor FedShat Shatokhin, Timofey IzhtskiyTimofey Izhitskyi, Egor salyg1n Salygin, Vladimir plagues Gerasikov under the guidance of Evgenii pakhomovee Pakhomov

We are very thankful to

• teachers who contributed to the round creation: Kirill kirill.kligunov Kligunov, Alexey daubi Vasiliev, Anton stepanov.aa Stepanov and Fedor fastmath Ushakov

• testers for good advice and important feedback: KseniaShk, AndreyPavlov, glebustim, Semen07, Ooops_no, adventofcode, Sweezy, NToneE, Umi, DanilaOdesser, maomao90, Nikitun, a.stepanov281005, i_love_penguins, Kayot, LeoPro, exhausted, SomethingNew, AndrewPav, Dart-Xeyter, lgswdn

• Gimran bashkort Abdullin for reviewing all of the tasks and giving us valuable advice, which helped us improve the contest

• our coordinator IgorI for valuable advice and patience

• KAN for the help during preparation of the contest

• MikeMirzayanov and geranazavr555 for codeforces and polygon platforms

You will have 5 tasks and 2 hours to solve them. We recommend you read all the problems. The contest may contain interactive problems! Make sure to read this post.

The scoring distribution is $$$500-1250-1500-2000-(1750+1000)$$$

Note that the round has been moved one hour later. The contest start time is Aug/15/2023 17:35 (Moscow time)

We hope that you will enjoy our tasks!

Good luck!

UPD: Editorial

UPD 2: Congratulations to the winners!

Div. 2:

1. dong_liu

2. yydtq

3. wk______tzc

4. qwesda

5. Van_Dijk

Div. 1:

1. jiangly

2. neal

3. BucketPotato

4. kotatsugame

5. YocyCraft

First solves:

A. ball_of_wool

B. ecnerwala

C. nigus

D. jiangly

E1. grass8sheep

E2. yydtq

Hello, Codeforces.

We are happy to invite you to Codeforces Round 892 (Div. 2), which will take place on Aug/12/2023 17:35 (Moscow time). All of the problems are original and were prepared by a collective of authors, consisting of kristevalex, i_love_penguins, efimovpaul and me, induk_v_tsiane. This round will be rated for participants with a rating lower than 2100.

We would like to thank:

• Artyom123 for coordinating the round.

• maomao90, Umi, Qwerty1232 and Mangooste for GM testing.

• maks_matiupatenko, tiom4eg, ilyakrasnovv, sergeev.PRO, EJIC_B_KEDAX, Kihihihi, gmusya, zwezdinv, 74TrAkToR, Dominater069, TeaTime, antonis.white, nikuradze, satyam343, Noobish_Monk, AquaMoon, fishy15, meowcneil and green_gold_dog for Master and International Master testing.

• diskoteka, ArtAlex, MrEssiorx and makrav for CM testing.

• playerr17, dmikhalin, FelixDzerzhinsky, KiruxaLight, VolkovMA, Gornak40, Splatjov, v0s7er, arseny2606, Mr_Ell, qwexd and olyazyryanova for Expert testing.

• YakovLya and LinkCatList for Specialist testing.

• pazal for Newbie testing.

• And last but not least, MikeMirzayanov for the Codeforces platform and Polygon systems.

You will be given 6 problems and 2 hours to solve them. The score distribution is 500 — 1000 — 1250 — 1750 — 2250 — 3000.

I would like to also congratulate my cousin Max, who is turning 30 the day of the round. If you wish, you can write birthday wishes for him and I will pass them on.

UPD: Editorial

UPD 2: Congratulations to the winners!

Div. 2:

1. modulo998244353

2. botjiaxun

3. Tmath_OneLove

4. FengjianZhu

5. Alihan_8

Div. 1:

1. Geothermal

2. heno239

3. maspy

4. jiangly

5. Ormlis

Hello, my favorite community!

I’m in a hurry to tell you about a new event from our main sponsor — TON Smart Challenge #4!

An exciting 10 days contest that's open to both beginners and experienced FunC developers with a total prize fund of 30,000 TON begins on August 8th and lasts until August 18th, 23:59:59 UTC+4.

TON Smart Challenge #4 is designed to showcase the fundamental aspects of how smart contracts function in TON. Participants will have the opportunity to master complex cell manipulations, smart contract storage organization, comment handling, basic cryptography, and the logic of governance smart contracts through problem-solving.

To enter the challenge, simply register via the @toncontests_bot on Telegram. The bot will guide you through the registration process and keep you informed when the challenge starts, and the tasks are published. It will also help you submit your solutions as a legitimate participant.

More details about the contest and prize distribution one may find on the website.

But that’s not all the news!

In the early days of August was unveiled a new and improved TON Society.

TON Society, community of like-minded people united by the idea to contribute to the development of the TON ecosystem, has adjusted its philosophy and presents its improved version.

The mission of the upgraded community is to develop TON regional communities around the world, help enthusiasts organize offline meetings and attract local investors to work on TON projects.

To make this happen were established hubs in different regions worldwide:

• Europe
• SEA
• South Korea
• India

Builders and developers are welcome to join the TON Society and regional hubs.

Participating in TON Society means you’re aligning with the mavericks, forward-thinkers, the game-changers, and those who are shaping the world of TON.

Hello Codeforces!

We are pleased to invite you all to participate in Codeforces Round 891 (Div. 3), which will start on Aug/07/2023 17:35 (Moscow time).

The format of the event will be like any Div. 3 rounds:

• 6-8 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.

We encourage participants with a rating of 1600+ not to create new accounts but to participate unofficially.

Only trusted participants of the third 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 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 (or you are a newcomer/unrated), then the round will be rated for you.

Problems have been created and written by our team: FBI, Skillful_Wanderer, SashaT9 and Pa_sha.

We would like to thank

• MikeMirzayanov for creating Codeforces and Polygon.

• Vladosiya for coordination.

• nigus, YocyCraft, lis05, Nazar, welleyth, pavlekn, senjougaharin, Vladithur, DJeniUp, volochai, eggag32, moonpie24, shell_wataru, Kalashnikov, Bogdan1110, ksu_, zamong_juice, myav, sonyalytv for testing the round and making it better.

Good luck!

UPD: There was an error on problem F. We fixed the tests and rejudged solutions . We apologize for that. It only affected a few people whose solutions passes all tests now. Also some hacks were already added to the tests and broke some of solutions.

UPD2: Editorial

Hi, Codeforces!

Alexdat2000, Igorfardoc, and I are pleased to invite you to our Codeforces Round 890 (Div. 2) supported by Constructor Institute, which will be held on Aug/05/2023 17:35 (Moscow time). This round will be rated for participants with a rating lower than 2100.

We would like to thank:

• errorgorn for coordinating the round.
• Umi, maomao90, thenymphsofdelphi, Dominater069, Mike4235, valeriu, irkstepanov, zengminghao, Gheal, DeMen100ns, FEDIKUS, thanhchauns2, MinaRagy06, Java, xudian, madlogic, squishybanana04, stefanbalaz2, kobebryan9, Murinh0, IlyinAD, zamong_juice, Pemguimn, the_hyp0cr1t3, STommydx, peshkoff, AndZhi, revelcoS, Valenz, and tibinyte for testing the round and providing useful feedback.
• MikeMirzayanov for Codeforces and Polygon.

You will be given 5 problems, one of which is divided into two subtasks, and you will have 2 hours to solve them.

One of the problems will be interactive, so please read the guide for interactive problems if you are not familiar with it.

The score distribution is 500 — 750 — 1250 — 2000 — (1500 — 1500)

UPD: Tutorial

UPD2: Congratulations to the winners!

Div. 2:

1. AMDAM
2. Aoi_Minoa
3. baojiaopicua
4. Valaki2
5. JCY_

Div. 1:

1. neal
2. maspy
3. A_G
4. AmazingTalker_Frank
5. heno239

We are thrilled to share some exciting news with you! We are teaming up with our partner, Constructor Institute in Schaffhausen, Switzerland, to bring you an amazing opportunity: a round supported and organized in collaboration with Constructor Institute, where you can explore Master's programs in Switzerland. Now we pass the floor to our partner.

Hello, Codeforces community!

Constructor Institute in Schaffhausen (Switzerland) is pleased and proud to have the opportunity to support the round on Codeforces. We invite you to participate in it!

If you are passionate about studying in Switzerland and pursuing a Master’s degree, we encourage you to fill out the form to initiate the application process and scholarship interview. Our Institute representatives will be in touch with you to guide you through the next steps.

We offer two Master programs, both taught in English, with flexible duration of 1.5 or 2 years full-time:

• MSc in Computer Science, Software Engineering, and Leadership
• MSc in Quantum Software Engineering, and Computer Science

Our Master's programs open doors to a world of opportunities. Many of our students have secured high-profile roles in multinational companies in Switzerland and across the globe. Additionally, our programs also serve as an excellent preparation for Ph.D. research in fields such as software engineering, cybersecurity, artificial intelligence, and other advanced topics.

​​We understand that financing your education can be a concern, and to support your journey, we are offering the following scholarships:

• Tuition waiver scholarships — 20,000 CHF per year, covering the cost of tuition fees.
• Full scholarships — 20,000 CHF per year, covering the cost of tuition fees, along with a monthly stipend of 2,000 CHF to assist with living expenses in Schaffhausen.

Both scholarships are non-repayable, providing you with financial peace of mind.

To learn more about Constructor Institute and its programs, visit our webpage.

Eligibility for the programs and its available scholarships:

• You have obtained or you will obtain a Bachelor’s degree in Computer Science, Software Engineering, Physics, or a related field before the program starts.

To express your interest in this opportunity, please complete the form:

We wish you good luck in the competition and enjoy solving the problems.

Hello, Codeforces.

It's scary to think about it: there are already almost 1800 rounds in the list of past contests!

I started adding a filter to the table with these rounds. Right now, you can already filter by some of the types of rounds. Here's what I've supported:

• Div. 1
• Div. 2
• Div. 3
• Div. 4
• Div. 1 + Div. 2
• Educational Rounds
• CodeTON Rounds
• Globals
• Kotlin Rounds
• VK Cup Rounds
• Long Rounds
• April Fools

Of course, I might have forgotten some types of contests. Please remind me if I missed anything. We should pay attention only to types where we have conducted several contests of that type.

I plan to expand this filter by adding more settings. Perhaps it would be good to filter by the condition "has at least one submission in this contest" (or those for which no submissions at all). What do you think?

What else would you suggest adding?

P.S. Here is how it looks on the website (some intermediate version, some options may be missing).

I don't think comments like "you use X in model solution, author, are you an idiot?", "f**k you and your problems, they are shit" and such should be normal on Codeforces, especially when written by someone high-rated and/or respected in the community. I also don't think this kind of behavior should be normal towards regular users.

I know that sometimes contests can be frustrating. Sometimes it is the participant's fault, sometimes it is the problemsetter's fault, sometimes it just happens without anyone being guilty of that. And I understand that in some cases, the criticism the author receives is fair and well-deserved.

But there is a fine line between criticism, saying that you didn't like the problems, and hurling insults against the author. The former two are acceptable (and sometimes even needed, because authors have to improve and learn from their mistakes); the latter one, in my opinion, should not be acceptable.

It's not like we can ever get rid of offense and hatred completely; there will always be people who want to take it out on the community as a whole or someone specific. And if I created a blog for every time I saw an insult hurled towards me or some other member of the community, my account would already be banned for spamming. But I think that the comments like the one linked in the first paragraph are especially dangerous and need to be dealt with.

Codeforces community is biased towards people with high rating and people who do something for the website. And this is sometimes a good thing; but it can also make people think that if a high-rated participant and a problemsetter allows himself (or herself) to be rude and offensive, then it is acceptable, and they are allowed to do it as well. That's why cases like this one are especially bad.

We can never get rid of offense and hatred, but please don't make it something normal. Everyone should be responsible for what they are saying or writing, but if your word has some weight in the community, then it also means some additional responsibility for you. Please don't make people think that insulting the author (or anyone else, for that matter!) is perfectly reasonable and fine — I doubt you will like the results of that.

UPD: It looks like the focus of the comment section has shifted towards discussing how to give constructive feedback to the problemsetters. This is certainly one of the points of the blog, but the main thing I wanted to state was that insults against anyone should not be acceptable. It's just that the problemsetters usually get the most of the hatred on CF, so it's much easier to find the examples of that. But this behavior towards regular users should not be allowed either.

UPD2: Initially, there was a link to the comment which caused me to write this whole blog (a comment by a high-rated user and a problemsetter when he openly called another problemsetter retarded because of some details of the solution). I wanted to show it as a clear example, but it was not the right thing to do.

To the person whose comment I used as an example (if you're reading this): I apologize, I shouldn't have made it seem like you're the culprit, and I didn't understand the consequences of my blog fully. I know that you have openly admitted your mistake, and I admire you for that. If the fact that I've used you as an example made you feel awful, or made some other people call you out — I am terribly sorry.

Ciao, Codeforces! We're glad to invite you to take part in Codeforces Round 889 (Div. 1) and Codeforces Round 889 (Div. 2), which will start on Jul/29/2023 17:35 (Moscow time). You will be given 6 problems and 2 hours and 30 minutes to solve them in both divisions.

• One of the problems will be divided into two subtasks.
• One of the problems will be interactive, so please read the guide for interactive problems if you are not familiar with it.

The problems were authored and prepared by akifpatel, dario2994, Kaey and me.

We would like to thank

• dario2994 for his energetic coordination;
• Alexdat2000 for Russian translation;
• Vladithur, errorgorn for VIP testing;
• ALeonidou, antontrygubO_o, buffering, cry, emorgan, jamesbamber, MatteoArcari, MrBrionix, MyK_00L, pwned, zamong_juice for testing;
• MikeMirzayanov for creating Codeforces and Polygon.

Score distribution:

• Div. 1: $$$(750 + 750) - 1500 - 1500 - 2000 - 2750 - 3250$$$
• Div. 2: $$$500 - 1000 - (1250 + 1250) - 2500 - 2500 - 3000$$$

We hope you'll like the problemset!

Update 1: the editorial is out.

Update 2: congratulations to the winners!