BOJ 1018

체스판 다시 칠하기

N, M = map(int, input().split())
board = list()
for i in range(N):
    board.append(input())
repair = list()
for i in range(N-7):
    for j in range(M-7):
        first_W = 0
        first_B = 0
        for k in range(i,i+8):
            for l in range(j,j + 8):
                if (k + l) % 2 == 0: 
                    if board[k][l] != 'W':
                        first_W = first_W+1
                    if board[k][l] != 'B':
                        first_B = first_B + 1
                else: # (0,1) (0,3) (1,0)
                    if board[k][l] != 'B': 
                        first_W = first_W+1
                    if board[k][l] != 'W':
                        first_B = first_B + 1
        repair.append(first_W)
        repair.append(first_B)
print(min(repair))