CodeChef June Cook-Off invitation

Правка en3, от Morphy, 2017-06-18 22:20:25

Hello Codeforces!

I’d like to invite you to CodeChef June Cook-Off that will start at 21:30 IST of 18th June 2017 (check your time zone here). There will be 5 problems and it will last 2.5 hours.

This is my second Cook-off, my previous round was on august 2016 — at this rate my rounds are going to be called Alei yearly contests!

  • Problem Setter: Alei Reyes Morphy
  • Primary Tester and editorialist: Hussain Kara Fallah Pepe.Chess
  • Secondary Tester: Kacper Walentynowicz kpw29
  • Mandarin Translator: Hu Zecong huzecong
  • Vietnamese Translator: Team VNOI
  • Russian Translator : Sergey Kulik CherryTree

No registration is required, anybody with a CodeChef handle can participate.

Hope you enjoy the puzzles!

UPD. I'm really sorry for the inconvenient with problem KNICOV. Testers also arrived to the same greedy solution and I was overconfident since it was an easy problem.

UPD. Hints, comments, solutions

ADACRA: Group Us and Ds in blocks, what happens with the number of blocks after performing one operation?

SNACKUP: I came up with this problem while doing research on the double cycle cover conjecture. The problem is about finding a set of cycles such that every edge is in exactly two cycles.

CENTREE

KNICOV: This was expected to be the easiest problem of the round, I underestimated it and now you can see the consequences.

For n=2 the answer is

..**.. ..**.. ..**..
..**.. ..**.. ..**..

For n=3 I thought that the same patterns produce the correct answer but it turns out that fewer knights are required. I had a proof, but it was incorrect :(

I missed the dp solution which is the bulletproof

ADADET: ~10 minutes before the round I generated new test data, but solutions of testers didn't match! I got very nervous, it turns out that I was comparing files with diff and the testers output were in differente format (spaces, line breaks). Hint: Think in the structure of the convex hulls.

История

 
 
 
 
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  Rev. Язык Кто Когда Δ Комментарий
en3 Английский Morphy 2017-06-18 22:20:25 1350 Tiny change: 'NTREE** \n![ ](/pr' -> 'NTREE** \n\n![ ](/pr'
en2 Английский Morphy 2017-06-17 01:20:36 14 (published)
en1 Английский Morphy 2017-06-17 01:07:32 1050 Initial revision (saved to drafts)