Hi, Codeforces! Glad to announce a design competition for Codeforces T-shirts:)

Conditions:

• Design must reflec- t belonging to Codeforces community.
• Short and brief motto is important. Phrase outline can be an additional instrument for expression of idea. An interesting motto can also participate in the competition.
• Idea is important for a printing. It's not neccessary to implement it fully if you don't feel your skill level right. You can describe your idea with a sketch/text description and that would be enough.
• T-shirt's background can be white or black.
• The winner will be determined by Codeforces team according to community opinion.

We consider this options as good ones:

We're waiting for your options during this two weeks. Last day – 14 February. We'll send 3 T-shirts with new design to the winner!

May the creative be with you ;)

UPD: Thank you all for participation! Results will be announced on February 22.

Hello, Codeforces!

It's my honor to invite you to Codeforces Round #460 (Div. 2), which takes place at 13:05 UTC, January 31st. The round will be rated for all division 2 participants. Also we warmly welcome those division 1 participants to join us out of competition. Note that round starts in the unusual time! :)

This round is prepared by me and my friend wuminyan0607. Many thanks to my friend for helping me testing the round and generating testcases. Besides, many thanks to the Codeforces coordinator KAN for giving me a chance to hold this round, testers cdkrot, cyand1317, demon1999, Glebodin, vintage_Vlad_Makeev, FalseMirror for testing this round and MikeMirzayanov for the great Codeforces and Polygon platforms. Without their huge effort, this round would't be possible.

Hope you can find these problems interesting. Wish all of you fewer bugs and higher rating!

The scoring distribution will be announced soon.

UPD1: There will be 6 problems and you have 2 hours to solve them. The scoring distribution will be 500-750-1000-1500-2000-2500.

UPD2: System test is over. Hope you will like those problems. Congratulations to the winners!

Div. 2

1. OO0OOO00O0O0O0O00OOO0OO (Solved all 6 problems and got 4 successful hacking attempts)

2. pannibal (Solved all 6 problems)

3. sasasagagaga

4. answerrtx

5. Kemal

6. Ren_shimosawa

7. UoA_Kanade

8. just_soso

9. jijiang

10. TayTayTayTaylor

Div. 1 & Div. 2

1. KrK

2. Vercingetorix

3. OO0OOO00O0O0O0O00OOO0OO

4. uwi

5. black_horse2014

6. TonySnark

7. zscoder

8. Marco_L_T

9. quailty

10. pannibal

UPD3: Editorial is ready!

Hello, Codeforces!

The First International Data Analysis Olympiad (IDAO) Began Online This January — Finals To Be Held This April in Moscow, Russia.

This is the best time to join the competition. It will be running until February 11th and the problems will be in English — if you want to take part and win a prize, register now.

Higher School of Economics, Yandex and Sberbank along with Harbour.Space University are proud to announce an olympiad created by and for data analysts.

The event aims to bridge the gap between the all-increasing complexity of Machine Learning models and performance bottlenecks of the industry. The participants will strive not only to maximize the quality of their predictions, but also to devise resource-efficient algorithms.

This will be a team machine learning competition, divided into two stages:

• The first stage will be online, open to all participants.
• The second stage will be the offline on-site finals, in which the top 30 performing teams from the online round will compete at the Yandex office in Moscow.

We would like to thank the IDAO team for their amazing work in problemsetting — Dmitry Vetrov, Andrey Chertok, GlebsHP, Alexander Guschin, Michael, Konstantin Mertsalov, Evgeny Sokolov, Vadim Strijov, Nick Tiden, Dmitry Ulyanov, Andrey Ustyuzhanin.

More information and register

STAGE 1. ONLINE

There will be two separate tracks during the online stage. From the machine learning perspective, the tracks will be similar, yet the restrictions put on the solutions are different for each track.

We hope that the two tracks will make the olympiad fascinating for both machine learning competition experts and competitive programming masters, Kaggle winners and ACM champions, as well as everyone eager to solve real world problems with Data. Moreover, we encourage people with different backgrounds, ML and ACM, to team up and push Data Analysis to new frontiers.

The first track will be a traditional data science competition. Having a labeled training data set, participants will be asked to make a prediction for the test data and submit their predictions to the leaderboard. In this track, participants can produce arbitrarily complex models. If you like to use 4-level stacking or deep neural networks, this is the right track for you – you will only need to submit test predictions. However, those who qualify for the finals will be asked to submit the full code of the solution for validation by the judges.

In real world problems, efficiency is as important as quality. Complex and resource-intensive solutions will not fit the strict time and space restrictions often imposed by an application. That is why in the second competition track, your task will be to solve the same problem as was in track one, but with tight restrictions on the time and on the memory used during both learning and inference. You will need to upload the end-to-end code for your solution: both learning and inference. The evaluation server will run training and testing for your model and report the result. Both learning and evaluation must fit into time and memory constraints. If you like the most efficient solutions, this is the right track for you.

PRIZES

Winners of the first stage will be invited to Moscow to take part in the on-site competition. Accommodation, and half-board meals are covered by the organising committee.

All participants have the chance to showcase their skills to the data science community on an international scale — the results will be internships, networking with some of the most passionate and like minded individuals, and job opportunities.

For winners, valuable prizes will be awarded, with both Higher School of Economics and Harbour.Space University offering special awards. Students from outside of Russia will have an opportunity to join a Master's degree programme at HSE, within the Faculty of Computer Science, free of charge. From Harbour.Space University, a 29,000 EUR scholarship will be offered, which also covers living costs in Barcelona, for graduate and undergraduate degrees.

Special prizes might be awarded at the discretion of the jury.

The winners will be determined by the leaderboard ranking based on private test set.

More information and register

I'm honored to announce that Codeforces round #459 is going to take place on January 29th and Reyna and I are the problemsetters of this round.

I'd like to thank keyvankhademi, AlexFetisov, winger, Belonogov, cyand1317 and demon1999, AnPelec for testing, KAN for coordinating the round and MikeMirzayanov for the great Codeforces and Polygon platforms.

The main characters of the round are Stranger Things characters.

The scoring distribution will be announced soon.

Good luck and have fun.

UPD0: The round is over, we hope you enjoyed it. Editorial will be posted soon.

UPD1: System testing is over, congratulations to the winners.

Div.1 winners are:

1. jqdai0815
2. FizzyDavid
3. ainta
4. aid
5. Swistakk

And Div.2 winners are:

1. Omar_Morsi
2. Chaarzeh (Interesting :-?)
3. magicalCycloidea
4. Tanzir5
5. UoA_Kanade

The editorial will be posted in a bit.

UPD2: Here's the editorial. Also please help me and Reyna do better next time by filling out this form.

I think it's good time for collecting teams that are going to WF this year. Let's complete the table together :)

Europe

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Hello Codeforces!

I would like to invite you to CodeCraft-18, which will take place on Saturday, 20th January, 9:05 PM IST. This is a combined Div. 1 + Div. 2 round and is rated for participants of both divisions.

CodeCraft-18 is part of Felicity, IIIT Hyderabad's most awaited set of events, Threads. With a plethora of intellectually engaging online contests in various fields of programming, mathematics and general knowledge, Threads is a celebration of the spirit of computing and engineering. Other than CodeCraft, we have the Project Euler-style contest Gordian Knot and a jeopardy-style CTF event called Break In, amongst other events.

I would like to thank the CodeCraft team -- FundamentalEq, RohanRTiwari, additya1998, aman_shahi2, born2rule, codelegend, crvineeth97, deepanshugarg, devanshg27, mprocks, nir123 and virus_1010 -- for their amazing work in problemsetting. I would also like to thank vintage_Vlad_Makeev for helping us prepare the problems, and MikeMirzayanov for the great Codeforces and Polygon platforms.

Prizes

• Top 20 participants win Codeforces T-shirts
• Top 5 participants from India win Codeforces T-shirts

You will be given 8 problems and 3 hours to solve them. The scoring distribution will be announced later. Good luck!

Update: Scoring is 500 — 1000 — 1500 — 2000 — 2500 — 3000 — 3500 — 3750

Update 2: We would like to apologize about problem F and G, which turned out to be easier than we expected, and about the mistake in the statement of H.

Congrats to the winners!

Top 20:
1. SkyDec
2. Syloviaely
3. matthew99
4. dotorya
5. FizzyDavid
6. laofudasuanbaofushehui
7. ikatanic
8. jcvb
9. Um_nik
10. molamola.
11. rajat1603
12. geniucos
13. MrDindows
14. Radewoosh
15. pavel.savchenkov
16. shanquan2
17. 613
18. JOHNKRAM
19. mxh1999
20. satyaki3794

Top 5 in India:
1. rajat1603
2. satyaki3794
3. jtnydv25
4. akulsareen
5. akashdeep

The editorial is ready!

Hello Codeforces! Some months ago I wrote tutorial about basics of recurrent sequences. This blog, my second tutorial is about mine another favorite topic — Invariants and Monovariants. These are useful concepts which will help you solving problems, especially, constructive ones. Even if you are not familiar with this topics, I'm sure that you solved problems with use of invariants and monovariants without knowing it, continue reading, you will understand my point :) There will be hard problems which are based on old IMO problems, so I will try my best to explain solutions of examples.

So, what are Invariants and Monovariants? An invariant is a quantity that doesn't change. A monovariant is a quantity that changes monotically (that is, non-decreasing or non-increasing). Seems simple, yes?

Let's start with a few easy examples which you will better understand its point. I suggest you to try solving problems by your own before reading solution.