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Classrooms with rare capacities

Source: Mexican Quarantine Mathematical Olympiad P2

April 25, 2020
combinatoricsrelations

Problem Statement

Let nn be an integer greater than 11. A certain school has 1+2++n1+2+\dots+n students and nn classrooms, with capacities for 1,2,,n1, 2, \dots, n people, respectively. The kids play a game in kk rounds as follows: in each round, when the bell rings, the students distribute themselves among the classrooms in such a way that they don't exceed the room capacities, and if two students shared a classroom in a previous round, they cannot do it anymore in the current round. For each nn, determine the greatest possible value of kk.
Proposed by Victor Domínguez