Leetcode 3648. Minimum Sensors to Cover Grid

Place sensors that each cover a square of side length 2k+1 under Chebyshev distance; the task is to minimize sensors to cover an n×m grid, which reduces to tiling the grid with (2k+1)×(2k+1) blocks. Thus the minimum number is ceil(n/(2k+1)) * ceil(m/(2k+1)).