1018.cpp

#include <iostream>
#include <string>
#include <algorithm>
using namespace std;

const int INF = 987654321;
const int MAX = 50;
int M, N;
string board[MAX];
//(0, 0)이 W인 체스보드
string whiteFirst[8] = {
    {"WBWBWBWB"},
    {"BWBWBWBW"},
    {"WBWBWBWB"},
    {"BWBWBWBW"},
    {"WBWBWBWB"},
    {"BWBWBWBW"},
    {"WBWBWBWB"},
    {"BWBWBWBW"}
};

//(0, 0)이 B인 체스보드

string blackFirst[8] = {
    {"BWBWBWBW"},
    {"WBWBWBWB"},
    {"BWBWBWBW"},
    {"WBWBWBWB"},
    {"BWBWBWBW"},
    {"WBWBWBWB"},
    {"BWBWBWBW"},
    {"WBWBWBWB"}
};

//(0, 0)이 W인 체스보드 기준 바뀔 칸 수

int whiteFirstChange(int y, int x)
{
    int cnt = 0;
    for (int i = y; i < y + 8; i++)
        for (int j = x; j < x + 8; j++)
            if (board[i][j] != whiteFirst[i - y][j - x])
                cnt++;
    
    return cnt;
}

//(0, 0)이 B인 체스보드 기준 바뀔 칸 수

int blackFirstChange(int y, int x)
{
    int cnt = 0;
    for (int i = y; i < y + 8; i++)
        for (int j = x; j < x + 8; j++)
            if (board[i][j] != blackFirst[i - y][j - x])
                cnt++;

    return cnt;
}

int main(void)
{
    cin >> N >> M;
    for (int i = 0; i < N; i++)
        cin >> board[i];
    int result = INF;
    for (int i = 0; i + 7 < N; i++)
        for (int j = 0; j + 7 < M; j++)
            result = min(result, min(whiteFirstChange(i, j), blackFirstChange(i, j)));

    cout << result << endl;
    return 0;
}