Yet another domino problem
Source: EGMO 2019 Problem 2
April 9, 2019
combinatoricsEGMO 2019
Problem Statement
Let be a positive integer. Dominoes are placed on a board in such a way that every cell of the board is adjacent to exactly one cell covered by a domino. For each , determine the largest number of dominoes that can be placed in this way.
(A domino is a tile of size or . Dominoes are placed on the board in such a way that each domino covers exactly two cells of the board, and dominoes do not overlap. Two cells are said to be adjacent if they are different and share a common side.)