Hello!

This time decided to fill myself in the shoes of the problem writers. It is very exciting! My challenge was to prepare a round in one day. It's really incredible pleasure to surrender to my passion and all day just work on problems!

Despite the fact that in total I've wrote 8 problems, I made it in time. Initially, I prepared 7 problems, but two of them were found to be used before (thank you, 300iq and cdkrot for poining it) and I removed them and wrote a new problem.

Codeforces Round 496 (Div. 3) will start on Jul/09/2018 18:35 (Moscow time). You will be offered 6 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. Probably, participants from the Div. 1 not be at all interested by this problems. And for 1600-1899 the problems will be quite easy. However, all of you who wish to take part and have 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. I tried to make strong tests — just like you will be upset if many solutions fail after the contest is over.

You will be given 6 problems and 2 hours to solve them.

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 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.

Many thanks to the testers: kevinsogo, 300iq, cdkrot, arsijo and adedalic. You really helped to make this round!

Good luck!

UPD 1: The round is over. Thank you for participation!

Official Top-5 (trusted only)

• poteryan_i_ne_naiden
• num2
• qaweqa
• HCMUS-Thanos
• tantam75

Unofficial Top-5 (+ untrusted)

• BigBag
• kmjp
• quailty
• TangentDay
• Aeon

UPD 2: The editorial is available by the link.

Microsoft's Quantum Team and Codeforces are excited to invite you to Microsoft Q# Coding Contest — Summer 2018!

The contest will run from July 6 — 9 and will consist of increasingly challenging tasks on introductory topics in quantum computing: superposition, measurement, oracles and simple algorithms. The top 50 ranked participants will receive a Microsoft Quantum T-shirt!

As a reminder, last weekend we help a warmup round with easier tasks which covered the same topics. The results were quite impressive: 167 participants solved all tasks! You can see the tasks here, and the solutions with explanations here.

Several useful reminders:

• The contest is unrated.
• Solutions are accepted in Q# only.
• Participants are ranked according to the number of correctly solved tasks, with penalty time as a tiebreaker.
• The tasks are grouped by topic, and the tasks within one topic are ordered in approximate order of increasing difficulty. If you find a problem too hard, don't forget to check the next problems in this topic and problems from different topics, they might turn out to be easier.
• Unlike the warmup round, you're not allowed to discuss the tasks during the contest.
• By popular demand, we have added Custom Invocation to allow you to run Q# code on Codeforces servers. Here is the signature of the code you should use to run it (note that the namespace and operation name have to match this code exactly):

namespace Solution {
    open Microsoft.Quantum.Primitive;
    open Microsoft.Quantum.Canon;

    // ------------- Operation which is called from C# -------------------
    operation RunQsharp () : Bool
    {
        body
        {
            Message("Hi");
            return true;
        }
    }
}

• For tasks which require you to create a certain quantum state or to implement a unitary transformation, any kind of error gives verdict "Wrong Answer". For tasks which have classical return, I tried to differentiate verdicts "Wrong Answer" (your return value was incorrect) and "Runtime Error" (array index out of bounds, qubits released are not in zero state, oracle called too many times etc.).
• NO PURCHASE NECESSARY. Must be 16 years of age or older. Game ends 7/9/18. For details, see Official Rules.

You can find the discussion of the warmup round and pointers to Q#/quantum computing materials here.

For first time Codeforces users:

1. Create user account here.
2. Register for the contest here.
3. Once the contest starts on July 6, access the problems here.

Good luck! We hope you enjoy the contest!

Update. The contest is over. Editorials are published.

Hi everybody!

Summer... It is a wonderful time for traveling, walking with friends, new discoveries and, of course, writing new exciting contests at Codeforces. Thus, I bring to your attention my new Codeforces Round #495 (Div. 2) with interesting tasks that will take place on Jul/05/2018 19:35 (Moscow time). If your rating is less than 2100, this round will be rated for you; otherwise, you can participate out of competition.

I would like to thank Mike MikeMirzayanov Mirzayanov for his help with problems preparing and for Codeforces and Polygon platforms. Also, Ildar 300iq Gainullin, Dmitry cdkrot Sayutin, Daniil danya.smelskiy Smelskiy, Chin-Chia eddy1021 Hsu, and Kevin ksun48 Sun for the problems testing.

You will be given 6 problems and 2 hours to solve them. Scoring distribution will be announced later.

In this round, you will have to help Sonya with her daily problems. Good luck!

UPD. Scoring 500-1000-1500-2000-2500-3000.

UPD. Congratulations to winners!!!!

Hello!

Codeforces Round 494 (Div. 3) will start on July 3 (Tuesday) at 14:35 (UTC). You will be offered 6 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. Probably, participants from the first division will not be at all interested by this problems. And for 1600-1899 the problems will be too easy. However, all of you who wish to take part and have 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. I tried to make strong tests — just like you will be upset if many solutions fail after the contest is over.

You will be given 6 problems and 2 hours to solve them.

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 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 MikeMirzayanov for the platform, help with ideas for problems and for coordination of my work. Thanks to Mikhail awoo Piklyaev, Maksim Neon Mescheryakov and Ivan BledDest Androsov for help in round preparation and testing the round.

Good luck!

UPD: Editorial

UPD2:

Congratulations to the winners:

Congratulations to the best hackers:

419 successful hacks and 670 unsuccessful hacks were made in total!

And finally people who were the first to solve each problem:

Hi, codeforces!

I am happy to invite you to the codeforces round #493, which happens at Jul/01/2018 17:05 (Moscow time).

This round writers are — Ildar 300iq Gainullin, Grigory vintage_Vlad_Makeev Reznikov, Mike MikeMirzayanov Mirzayanov, and me, cdkrot.

Big thanks for people, who tested round — Shiqing cyand1317 Lyu, Andrew GreenGrape Rayskiy, Ivan isaf27 Safonov, Alexey Aleks5d Upirvitsky. Also thanks to Mike MikeMirzayanov Mirzayanov and Nikolay KAN Kalinin for help with round preparation.

And to Mike MikeMirzayanov Mirzayanov for codeforces and polygon systems.

Traditionally, there will be 5 problems for 2 hours. I hope you will enjoy the problemset, good luck and have fun!

Scoring distribution will be published before the round.

UPD: Scoring distribution is as follows:

Div1: 500 1250 1500 2500 3000

Div2: 500 1000 1250 2000 2500

You may also want to check this post for post-contest stream.

UPD2: The editorial was published!

UPD3: Congratulations to winners!

Div1:

1. TLE
2. ksun48
3. fateice
4. Swistakk
5. Um_nik
6. Petr
7. V--o_o--V
8. consecutivelimit
9. LHiC
10. uwi

Div2:

1. kirisamejin
2. liu_runda
3. AntiLeaf
4. TheFallenOne
5. haj_lemon
6. st-Firdavs
7. traxex
8. paladin
9. kmyiu
10. Maxim

Hello, Codeforces!

On June 27, 17:35 MSK Educational Codeforces Round 46 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.

As usual, the round will be rated for the participants with rating lower than 2100. It will be held on extented ACM ICPC rules. 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 7 problems and 2 hours to solve them.

The problems were prepared by Adilbek adedalic Dalabaev, Roman Roms Glazov, Mikhail awoo Piklyaev and me.

Good luck to all participants!

UPD. The editorial is here.

I also have a message from our partner, Harbour.Space University:

Hi Codeforces!

For our programming boot camp’s next iteration of Hello Barcelona Programming Bootcamp, Harbour.Space University in collaboration with Moscow Workshops ICPC, ITMO University, Moscow Institute of Physics and Technology, Saint Petersburg State University and Codeforces is bringing the best training practices and coaches to Barcelona to prepare 150 students for winning medals in the next ICPC World Finals.

It's extraordinary to see the entire cultural spectrum meet at the boot camp over a common love of programming and learning, and this autumn, we will be doing it again.

Our boot camp will once again feature the all-time greats Mike MikeMirzayanov Mirzayanov, Andrey andrewzta Stankevich, Michael Endagorion Tikhomirov, Gleb GlebsHP Evstropov, Artem VArtem Vasilyev, Ivan ifsmirnov Smirnov and other world renowned Russian coaches to train the participants.

Expect the most challenging problems, surprise guests and speakers, a branded hackathon, and finally the online round held on Codeforces, so everyone can join the onsite participants, at the finale of the event.

During the nine days of the event from Sept 26 to Oct 4, 2018 in Barcelona, teams will be participating in practice contests, problem discussion sessions and lectures.

Learn more about Barcelona ICPC Bootcamp

You can ask any questions by email: [email protected]

UPD: The contest is over.

Congratulations to the winners:

Congratulations to the best hackers:

And finally people who were the first to solve each problem:

Hello denizens of Codeforces once again!

After our last two rounds, Yang Liu (desert97) and I (ksun48) are pleased to announce Codeforces Round #492, which will happen on June 24, 2018 at 19:35 MSK. There will be two versions of the contest, one for users in Division 1 and one for users in Division 2. Both versions will have six problems, with four problems shared between the versions.

The round will feature our friend and superstar member of ACM-ICPC team MIT TWO, Allen Liu (cliu568).

The scoring distribution will be visible once the contest begins. As usual, we'd like to thank our wonderful problem coordinator KAN and Codeforces administrator MikeMirzayanov, as well as the rest of the Codeforces staff for keeping this site an amazing place for competitive programming. Thanks also to our testy testers winger, AlexFetisov, and demon1999.

This round is in honor of uDebug who have supported Codeforces on its anniversary. Thank you, uDebug! uDebug is an enthusiastic community of competitive programmers who help each other out by answering questions on chat, providing hints and solutions to problems from several online judges, furnishing test input and sharing feedback. On uDebug, you can select a problem you’ve coded up a solution for, provide input, and get the "accepted" output. You can visit it by the link.

Good luck! As always, we encourage competitors to read all the problems.

(̶a̶l̶s̶o̶,̶ ̶I̶ ̶s̶e̶e̶m̶ ̶t̶o̶ ̶h̶a̶v̶e̶ ̶h̶e̶a̶r̶d̶ ̶s̶o̶m̶e̶ ̶r̶u̶m̶o̶r̶s̶ ̶f̶l̶o̶a̶t̶i̶n̶g̶ ̶a̶r̶o̶u̶n̶d̶ ̶a̶b̶o̶u̶t̶ ̶a̶ ̶s̶p̶e̶c̶i̶a̶l̶ ̶ ̶s̶u̶r̶p̶r̶i̶s̶e̶ ̶w̶h̶i̶c̶h̶ ̶m̶i̶g̶h̶t̶ ̶b̶e̶ ̶h̶a̶p̶p̶e̶n̶i̶n̶g̶ ̶d̶u̶r̶i̶n̶g̶ ̶s̶y̶s̶t̶e̶m̶ ̶t̶e̶s̶t̶i̶n̶g̶,̶ ̶s̶o̶ ̶k̶e̶e̶p̶ ̶y̶o̶u̶r̶ ̶e̶y̶e̶s̶ ̶p̶e̶e̶l̶e̶d̶!̶)̶

EDIT: And the rumors are confirmed! Go to http://codeforces.com/blog/entry/60176 after the contest is over to discuss the problems or voice your complaints along with scott_wu and ecnerwala!

EDIT: Due to some last minute changes, each version will have six problems, with four shared problems.

EDIT: The Div. 2 score distribution is 500-1000-1500-1750-2500-2750 and the Div. 1 score distribution is 500-750-1500-1750-2250-2500.

EDIT: Congratulations to the winners of the round!

Div. 1:

1. jqdai0815

2. Swistakk

3. Um_nik

4. bmerry

5. ainta

Div. 2:

1. Fortin

2. Aleks5d

3. KsCla

4. hopcroftkarp

5. davidberard

Thanks to everyone for participating! The editorial is available at http://codeforces.com/blog/entry/60217.

Hello!

Codeforces Round #491 (Div.2) will start this Saturday, June 23, 18:35 (UTC+3). This round will be rated for the participants with rating lower than 2100 and other contestants can join it out of competition.

This round problems have a significant intersection with NNSU Programming Contest 2018. Please do not participate in the round if you participated in the NNSU contest or tried to upsolve the problems.

During the round you have to help student Vasya to manage the difficulties caused by the end of the academic year. There will be 6 problems and 2 hours to solve them. If you solve all the problems in 25 minutes you will be able to watch the second half of South Korea — Mexico at the FIFA World Cup.

The scoring is unusual a bit: 500-1000-1250-1500-2000-2750

Great thanks to Mikhail MikeMirzayanov Mirzayanov for the well-known platforms; Nikolay KAN Kalinin — for the help with problems and the round coordination; Mikhail mike_live Krivonosov, Alexey Livace Ilyukhov, Nikita FalseMirror Bosov, Andrew GreenGrape Rayskiy and Alexey Aleks5d Upirvitskiy — for the round testing; Arseniy arsor Sorokin — for the statements translation. And good luck to all contestants!

UPD: The round is over, thank you for the participation!

UPD: Congratulations to the winners!

Div. 1:

1. nuip
2. krijgertje
3. qoo2p5
4. hohomu
5. neal

Div. 2:

1. King — solved all the problems, well done!
2. Daniar
3. Saidjamol
4. shoemakerjo
5. Toki_Time-Tinker

UPD: The editorial is published

Hello!

Codeforces Round 490 (Div. 3) will start on June 21 (Thursday) at 14:35 (UTC). You will be offered 6 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. Probably, participants from the first division will not be at all interested by this problems. And for 1600-1899 the problems will be too easy. However, all of you who wish to take part and have 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. I tried to make strong tests — just like you will be upset if many solutions fail after the contest is over.

You will be given 6 problems and 2 hours to solve them.

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 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 MikeMirzayanov for the platform, help with ideas for problems and for coordination of my work. Thanks to Mikhail awoo Piklyaev, Maksim Neon Mescheryakov and Ivan BledDest Androsov for help in round preparation and testing the round.

Good luck!

UPD: Also great thanks to step_by_step, kevinsogo and nhho for help in round preparation and testing the round.

UPD2: The results table!

Congratulations to the winners:

Congratulations to the best hackers:

110 successful hacks and 226 unsuccessful hacks were made in total!

And finally people who were the first to solve each problem:

UPD3: Editorial

Hi, Codeforces! I'm glad to invite everybody to the #489 Codeforces Round, which will be held as soon as tomorrow, on Monday, June 18, 2018 at 19:35. The round will be rated for all participants from the second division (with rating below than 2100). As usually, we will be glad to see participants from the first division out of competition!

Problems for the round have been invented and prepared by us, pupils of Moscow school №2007, Dmitry gop2024 Grigorev and Fedor ---------- Ushakov. We want to give thanks to Andrew GreenGrape Raiskiy for his aid in preparing and testing of the problems, to Ildar 300iq Gainullin and to AmirReza Arpa PoorAkhavan who have tested our problems too and to the coordinator Nikolay KAN Kalinin, since our sometimes strange and undeveloped ideas have become eventually the Codeforces round. Also, we say thank you to Mike MikeMirzayanov Mirzayanov for his unbelievable Codeforces and Polygon platforms.

You will receive 5 problems and 2 hours for solving it. During the round you will be helping for an extraordinary girl Nastya, who has been living in Byteland and sometimes receives very strange gifts for her birthday :).

Score distribution will be announced, traditionally, closer to the start of the contest.

We're holding our the first and, I hope, not the last round in Codeforces, so I hope a lot you will like our problems. Please, read all the problems. Anyway, I wish luck and high rating for all the participants!

I'm looking forward your participation.

UPD Score distribution is standart — 500-1000-1500-2000-2500

UPD2 Thank you for your participation in the contest! It's very-very pleasant for me if you like the problems, and I'm sorry if you don't :) I hope the next my contest will be even better, than this. Thank you for all!

List of the winners of the contest:

Div.2

1. sminem

2. NguoiHocTinLoai2

3. YaKon4ick

4. HanaElhami

5. pajenegod

Div.1 + Div.2

1. dotorya

2. Benq

3. anta

4. sminem

5. kevinsogo

My frank congratulations for all the winners!

UPD3

Editorial is here