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 alei
- Primary Tester and editorialist: Hussain Kara Fallah Deadwing
- Secondary Tester: Kacper Walentynowicz Miyukine
- 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.
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.