Hi everyone!

Codeforces Round #448 (Div.2) takes place on 26th of November at 19:05 MSK. As usual, Div.1 participants can join out of competition.

This is my second round on Codeforces! I advise you to read all of the 5 problems. Hope everyone will find something interesting.

I'd like to thank vintage_Vlad_Makeev for coordination, igdor99 for helping me in developing problems. And, surely, thanks to Tommyr7, Arpa, 300iq for testing this round.

Of course, many thanks to MikeMirzayanov for great Codeforces and Polygon platforms.

Scoring: 500-1000-1750-2000-2250

High ratings to everybody!

UPD: Contest is finished. Editorial will be posted soon.

UPD: Editorial

Congratulations to the winners!!!

Div1

1. uwi

2. Benq

3. irkstepanov

4. dreamoon_love_AA

5. JustasK

6. eddy1021

7. yancouto

8. chemthan

9. Nephren_Ruq_Insania

10. KrK

Div2

1. Nephren_Ruq_Insania

2. Mahan_sh

3. lsrothy

4. ngfam

5. georgerapeanu

6. ZalBinHassan

7. mtkaya

8. Bodo

9. szhouan

10. fchirica

If you are 14+ and want your ideas to be implemented in new technologies and products, which being used by 1/3 of global population, participate in our Marathon started recently https://it-edu.mipt.ru/en/huawei-codecraft-marathon

Task can be downloaded after registration, see links below: John has a digital camera. He usually takes two photos, first photo is bad quality and blurred, second has good quality, but his hands shaked, and the second photo has moved compared to the first one. Help John to restore first(blurred) photo position, considering that the movement was in the same plane.

Solution: We highly encourage participants to use neural network based approaches for solving this task. You can download 30 samples from checker in txt format. Data generation for neural network training is one of the main point in our task. Converter from/to graphic format is also part of this task.

Registration can be done by captain. The team can consist from 1 to 3 team members: https://it-edu.mipt.ru/el/mod/apply/view.php?id=60 Checker http://huawei.it-edu.mipt.ru/marathon1 Rules https://it-edu.mipt.ru/en/huawei-codecraft-marathon/rules

Submission deadline is 2017 December 1, 23:59:59 Moscow time. Results will be announced on December 3 during the closing ceremony of 1/2 NEERC ACM ICPC 2017 at ITMO.

@stake are 9 internship certificates, 9 smartphones, several tours to HQ

Hello Codeforces!

On November 23, 18:05 MSK Educational Codeforces Round 33 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 an experiment, the round will be rated for Div. 2. It will be held on extented ACM ICPC rules. After the end of the contest you will have one day to hack any solution you want. You will have access to copy any solution and test it locally.

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

The problems were prepared by Mikhail awoo Piklyaev, Vladimir vovuh Petrov and me.

Good luck to all participants!

UPD: Editorial.

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

Be sure to join these courses to sharpen your programming and data analysis skills:

Combinatorics and graphs with Sergey Nikolenko, Researcher, Steklov Mathematical Institute at. St. Petersburg. He is a computer scientist with vast experience in machine learning and data analysis, algorithms design and analysis, theoretical computer science, and algebra.

Algorithms and Data Structures with Edith Elkind, Professor University of Oxford, Department of Computer Science. She researches game theory and the computation of social choices. She looks at the decisions involved in multi-agent systems such as auctions, elections and co-operative games.

Big Data Analysis: Mapreduce, Spark, BigTable/HBase, Distributed Data with Pavel Klemenkov and Alexey Dral. With HDFS, MapReduce, Spark, and NoSQL, students will master and sharpen their knowledge in basic technologies of the modern Big Data landscape.

Parallel and Distributed + High Performance Computing with Dalvan Griebler. The name says it all. Learn how to run your programs faster.

List of all courses:

27.11.17 — 15.12.17 — Image and Video Analysis with Archontis Giannakidis

27.11.17 — 15.12.17 — Linear Algebra with Archontis Giannakidis

08.01.18 — 26.01.18 — Text Mining & Translation with Sergey Nikolenko

08.01.18 — 26.01.18 — Combinatorics and graphs with Sergey Nikolenko

29.01.18 — 16.02.18 — Security analysis of networked objects with Yaroslav Rabovolyuk

19.02.18 — 09.03.18 — Security Operations Center and Cyber Threat Hunting with Sergey Soldatov and Teymur Kheirkhabarov

19.02.18 — 09.03.18 — Calculus with Dmitry Ivankov

12.03.18 — 30.03.18 — Malware Reverse Engineering with Vladislav Stolyarov, Victor Chebyshev and Boris Larin

09.04.18 — 27.04.18 — Incident Response & Digital Forensics with Konstantin Sapronov and Ayman Shaaban

09.04.18 — 27.04.18 — Linear algebra with David Zmiaikou

30.04.18 — 18.05.18 — Statistical Data Analysis with Evgeniy Riabenko

30.04.18 — 18.05.18 — Probability theory with Evgeniy Riabenko

21.05.18 — 08.06.18 — Parallel and Distributed + High Performance Computing with Dalvan Griebler

21.05.18 — 08.06.18 — Algorithms and Data Structures with Edith Elkind

11.06.18 — 29.06.18 — Big Data Analysis: Map Reduce, Spark, BigTable/HBase, Distributed Data with Pavel Klemenkov and Alexey Dral

Register for your spot

Innopolis University is organizing and holding Innopolis Open, an Olympiad in Informatics for high school students under 19 years old. The Olympiad consists of two stages — the online contest and the on-site competition (held in Innopolis, Russia).

Winners of the first stage will be invited to Innopolis to take part in the on-site competition. Accommodation, meals and transfer from Kazan to Innopolis are covered by the organizing committee. Winners of the second (on-site) stage will receive awards and opportunity to be enrolled in Innopolis University without any admission tests.

The first stage (online contest) will be held on:

• December 2, 15:00 (UTC +3)
• December 17, 10:00 (UTC +3)
  You may participate on both dates; the organizing committee will consider your best result. Registration is open until December 1, 2017. Participation is free of charge. The second stage (on-site contest) will take place in Innopolis city on February 24-25, 2018.

Click here to find out more and register for the Olympiad.

Stay in touch:

• Subscribe to our Telegram account to receive quick information and reminders.
• Contact us via e-mail: olymp@innopolis.ru
• Subscribe to our Facebook page.

Hello!

I am pleased to report that two rounds of Codeforces have gone quite well in terms of the work of Codeforces, I am very glad about it. These days nights I spent in a profiler, fixing the code, researching the settings of MariaDB.

In addition, I managed to allocate several hours on Sunday (to be honest, until Monday morning) to finish the long-planned innovation.

Meet, diagnostics of solutions in C++!

Many Codeforces visitors are already tired of the questions of less experienced participants: "Why does my solution not work on some test on the Codeforces servers, if I locally launch it and it works correctly? You have the wrong compiler/servers!" In 99% of cases this is an example of undefined behavior in a program. In other words, the program contains mistakes that, due to a number of circumstances, are not reproduced at local launch, but are reproduced at launch on the Codeforces servers.

Sometimes, it's not easy to notice such a mistake. A small overflow of the array can lead to an incorrect answer on the test and to an runtime error of the program.

In g++/clang++ there is a remarkable tools called sanitizers. It's such a way to compile a program in a special mode so that when it's working, it will check it for undefined behavior (and some other errors) and, if any, print them to stderr. The drmemory (it is similar to valgrind, but for Windows) has similar functionality, which starts the program in a special mode to detect errors. With such two diagnostic launches, the performance of the program suffers tremendously (the program is executed 5-100 times slower and requires more memory), but often it's worth it.

Now automatic diagnostics in some cases will prevent a question like "Why does not work ???", indicating the error or its appearance!

If your solution:

• written in C++,
• finishes with a verdict "wrong answer" or "runtime error"
• on this test worked extremely quickly and consumed a little memory,

then it will be restarted using special diagnostic compilers (clang ++ with sanitizers and g++ with drmemory). If an execution error occurs during this launch, the diagnostics log will be displayed in the test details in the "diagnostics" section. Of course, this entry will contain a technical report in English, but often it will indicate to you the error of the program. Often it contains the cause of the mistake and even the source code line. If the diagnostics are not displayed, then at least one condition above is not fulfilled or the diagnostics has not detected any errors.

Example of the diagnostics:  here it is written that there was an array out of range error in the line 78.

Thus, the diagnostics will sometimes help you to find a mistake like "out of bounds error", "signed numbers overflow", "uninitialized variable", etc. Carefully read the diagnosis and do not make such mistakes in the future!

I wish your programs did not fail. I hope the innovation will be useful!

There are big plans as it is useful to apply such diagnostics. Do not go far, wait for news, soon there will be more innovations!

P.S. Also, diagnostic compilers are simply available for use. For example, you can use them on the "Custom invocation" tab. I recall that the program runs many times slower and consumes more memory in diagnostic mode.

Hello, Codeforces!

I'm quite excited to invite you to participate in Codeforces Round #447 (Div.2 Only) which will be held on November 19 16:55 MSK.

All five problems are created by Zerui Cheng (Marco_L_T), Bingheng Jiang (NOIRP), Yiming Feng (whfym). And it's our first round on Codeforces. We want to show our great thanks to our school The High School Affiliated to Anhui Normal University and our coach Guoping Ye in competitive programming training.

And we also want to show our great appreciation to Mikhail Krivonosov (mike_live), Gleb Lobanov (Glebodin), Weihao Zhu (Tommyr7), Shiqing Lyu (cyand1317) for testing the problems, to Nikolay Kalinin (KAN) for coordination and to Mike Mirzayanov (MikeMirzayanov) for the fantastic Codeforces and Polygon platforms. The round can't be realized without their great help.

The contest will consist of 5 problems and you'll be given 2 hours to solve them. As usual, the scoring will be announced shortly before the start of the contest.

The contest is rated for Div. 2 contestants. And the same as before, Div. 1 contestants can take part out of competition.

Wish everyone high rating and bugless code!

See you on the leaderboard!

Clarification: In the mail, it reads that the duration is 2 hours and 30 minutes and it'll contain 6 problems. There's a mistake. The duration of the contest is 2 hours and there will be 5 problems.

UPD1: Scoring: 500-1000-1500-2000-2500

UPD2: The contest is finished! Have fun hacking!

UPD3: The system test is finished! Congrats to the winners!

And do you find something interesting in the statements,especailly for Chinese contestants?

Div.1 & Div.2:

1. fateice_ak_ioi (solved all the problems and got 22 hacks)

2. peace (solved all the problems and got 10 hacks)

3. dreamoon_love_AA

4. KrK (solved all the problems)

5. Benq (solved all the problems)

Div.2:

1. fateice_ak_ioi (solved all the problems and got 22 hacks)

2. peace (solved all the problems and got 10 hacks)

3. ec24 (made 16 hacks)

4. daaaaaaaaaaaaaaaaaaa

5. QYitong1

UPD4: Maybe you're complaining that there're too many hacks and the pretests are so weak,but it's our intention to do so. We regard hacks as a very important part and a feature of Codeforces.Do you agree?

UPD5: Editorial

Maybe B and C are a little harder than before,we'll be cautious about this next time.

Hope you have fun in solving the problems and hacking!

See you next time!

Hi Codeforces!

I'd like to invite you to join Codeforces Round #446 which will be held on November 17 at 17:35 MSK.

And yes it is rated.

The contest is prepared by Omid Azadi (omidazadi), Mehrdad Saberi (Batman), Arshia Soltani (ckodser), Aryan Esmailpour (Aryan) and me (I honestly didn't do anything).

And also thanks to Mahdi Amiri (Amiri), AmirReza PoorAkhavan (Arpa) for helping us, Weihao Zhu (Tommyr7) for testing the round and Nikolay Kalinin (KAN) for round coordination and Mike Mirzayanov (MikeMirzayanov) for awesome platforms Codeforces and Polygon.

You will have 2 hours and 5 problems each division.

Contest theme will be about Seven Deadly Sins but the statements will be short and brief.

The scoring distribution will be posted soon and good luck and stuff.

Update 1 : The scoring for both divisions is 500 — 1000 — 1500 — 2000 — 2500.

Update 2 : The round is over. Hope everybody had fun and enjoyed it. And as you can see the round is rated so yay!

Top 5 Div1 participants :

1.jqdai0815 (The only one who solved all problems)

2.Radewoosh

3.dotorya

4.SkyDec

5.ksun48

Top 5 Div2 participants:

1.shoob

2.mosthenio

3.SLLN

4.fdoer

5.dl1997

The editorial is posted.

Hey everyone!

Good news — Russian AI Cup 2017 has started! This competition is being held for the sixth time, and this time, hopefully, we will make happy all the fans of the RTS game genre — you will be controlling 500 vehicles of 5 different types at once. The task is to destroy the opponent!

Try yourself in creating an artificial intelligence, it's simple and fun. Go to Russian AI Cup site and enter the battle. Good luck!