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CGMO 2021 P3

Source: CGMO 2021 P3

August 14, 2021
combinatoricsColoring

Problem Statement

Find the smallest positive integer nn, such that one can color every cell of a n×nn \times n grid in red, yellow or blue with all the following conditions satisfied: (1) the number of cells colored in each color is the same; (2) if a row contains a red cell, that row must contain a blue cell and cannot contain a yellow cell; (3) if a column contains a blue cell, it must contain a red cell but cannot contain a yellow cell.