https://www.codechef.com/problems/EFFPAINT This is a challenge problem in codechef where we have to minimize the score. Can someone explain a good approach for this problem.

Also this is the editorial for the problem https://discuss.codechef.com/questions/6549/effpaint-editorial

I am not able to understand the editorial. The use of terms cells, rectangles and corners is not much clear in it. Can someone please explain this approach? One can refer to the setter's solution for better understanding on the approach used.

Kindly help.