Minimax

Let's consider a square grid with N rows and N columns, both numbered 1 through N. Each cell contains one integer. Let ri denote the minimum value in the i-th row, and let Ci denote the maximum value in the i-th column. A grid is called nice if and only if the following condition holds true: max(r1, r2, ..., rN) = min(C1, C2, ..., CN) Chef has a square grid and can change some of its elements