From Math Olympiad
Given an n×n grid, where n
is even, what is the minimum number of marks it takes to cover the grid?
- A mark covers the 4-neighbors of a square, that is the squares directly above, below, and to the left and right.
- A mark does not cover the squares diagonal to the marked square, nor does it cover itself.
- A grid is covered if and only if all the squares are covered.