We hope you enjoyed the whole problemset even though there were some technical difficulties.

Hi Codeforces!

The 27th Central-European Olympiad in Informatics takes place from 23-29 August in Nagykanizsa, Hungary. The mirror contests will be held on Aug/26/2020 15:05 (Moscow time) and Aug/28/2020 15:05 (Moscow time) (one day after each official contest day) here on Codeforces in the usual IOI format (it is unrated, the best scoring submission counts, scoreboard is not visible during the contest and there's full feedback throughout the whole contest).

In this year's CEOI, the 4 best problem solvers going to secondary schools of Austria, Croatia, Czech Republic, Germany, Hungary, Italy, Lithuania, Poland, Romania, Slovakia, Slovenia, Switzerland, and The Netherlands will compete. Due to the current situation, unfortunately not everyone will be able to make it onsite, but we hope the offsite participants will also enjoy the event, although without the magical week in Nagykanizsa.

Each day will feature a 5-hour contest. In both contests, you will be given 3 problems with a maximum of 100 points to score on each. Every task has subtasks of varying difficulties, so we hope everyone from newbie to legendary grandmaster will have fun solving the problems (well, legendary grandmasters might want to refer to the instructions here).

We would like to thank MikeMirzayanov for creating Codeforces and Polygon platforms and his invaluable help in making this mirror contest possible, and all of the organizers and sponsors.

We wish you will enjoy the contest just as much as we enjoyed preparing it!

CEOI 2020 Scientific Committee

Gyula Horváth, Attila Gáspár, birka0, busamate, csandras, Emarci15, leanil, mraron, lacito, uno20001

UPD1: The tutorial for day 1 is here.

UPD2: The tutorial for day 2 is here.

Sorry for the issues with the queue and with the bug interactor of potion causing python solutions to fail. Hope you still enjoyed the problems!

Congratulations to everyone who participated, here are the top 5 combined scores:

• WZYYN 600pts!
• jiangly 600pts!
• mnbvmar 573pts
• wucstdio 573pts
• 142857 530pts

The rest of the combined scores can be found here.

You can also check how would you fare against the official contestants on this ranklist.

We hope you liked the problems. See you on day 2 :D

Hello,

It's from Innopolis Open, Final Round, 2015-2016, the problem A. I can't approach it, can somebody give me a hint?

Have nice day,

mraron

Hi!

I've a problem with this problem, could anyone help me out with a hint? Anything is appreciated :)

Statement: There's a museum made up by N * N cells, forming a square. We should place N guards, so that in every column and row there's exactly 1 guard. Also the guards have their "preferences", so every of them have a rectangular area where he wants to be placed to guard. The problem is to give a distribution of the guards (N points) where everyone is in his preferred rectangle or state that there's no such distribution.

Here's the statement in hungarian language with a picture too: here.

Thank you for reading, have a nice day.

Hi!

I'm trying to solve UVa 12732, but the judge gives me wrong answer. My idea is that if I have n numbers then I compare two disjunct group of integers. This way in one query I can reduce the set of potential heavier coins from n to , and then I do the same on these potential heavier coins, until there will be a trivial case like only one or two coins remained. So it does queries I think. And for 3 ≤ n ≤ 120 it's less or equal than 5. Could anyone help my why does it get this verdict?

Here is my code: http://ideone.com/XYG4fz

Have a nice day.

mraron

Hi!

I'm trying to solve 525D-Arthur And Walls, but something strange is happening. First it TLEd at test #25. Then I did some optimizations on it, and submitted, I was very happy because it passed a lot of tests, but then an interesting thing happened! At test #91, it aborted the whole judging with "Denial Of Judgement" verdict. I'm confused because I never saw that verdict.

What's the problem with my solution? (Here are they: 10984580 10984546)

Thanks for any advice or explanation!

PS.: If its an commonly known thing, please don't blame me, I'm pretty new there :)

mraron