MathDB
Shading a Square Grid

Source: 2nd Final Mathematical Cup Junior Division P3 (2020)

October 1, 2020
combinatoricssquare grid

Problem Statement

Let kk,nn be positive integers, k,n>1k,n>1, k<nk<n and a n×nn \times n grid of unit squares is given. Ana and Maya take turns in coloring the grid in the following way: in each turn, a unit square is colored black in such a way that no two black cells have a common side or vertex. Find the smallest positive integer nn , such that they can obtain a configuration in which each row and column contains exactly kk black cells. Draw one example.