C: Palindromic Matrix

I used classification to solve it. The official solution uses brute force

Given H and W, we can tell how many positions has 4 mirrors, 2 mirrors, and 1 mirror

So for each letter, we try to fit it into 4 mirrors, 2 mirrors, and 1 mirror, in that order one by one

The answer is no if when we run out of possible 1 mirror positions. Otherwise, yes.

D: Four Coloring

  1. Covert Mahattan distance to Chebyshev Distance

  2. Divide the converted grid into d * d squares

  3. assign each 4 sqaures 4 colors. It is correct because each pair with distance d is in neighboring converted squares