2021 ICO Advanced P7
Source:
August 9, 2021
combinatorics
Problem Statement
In a group of people, of them are \emph{saboteurs}. Sherlock wants to find one saboteur. There are some missions that each needs exactly people to be done. A mission fails if at least one of the three participants in that mission is a saboteur! In each round, Sherlock chooses people, sends them to a mission and sees whether it fails or not. What is the minimum number of rounds he needs to accomplish his goal?