ソースコード
#include <cstdio>
#include <algorithm>
using namespace std;
int main() {
int N, M;
int F[51][3] = { {} };
scanf("%d%d", &N, &M);
for (int i = 1; i <= N; i++) {
for (int j = 0; j <= M; j++) {
char c;
scanf("%c", &c);
switch (c) {
case 'W':
F[i][0]++;
break;
case 'B':
F[i][1]++;
break;
case 'R':
F[i][2]++;
break;
default:
break;
}
}
F[i][0] += F[i - 1][0];
F[i][1] += F[i - 1][1];
F[i][2] += F[i - 1][2];
}
int ans = 0;
for (int i = 1; i <= N - 2; i++) {
for (int j = i + 1; j <= N - 1; j++) {
ans = max(ans, F[i][0] + F[j][1] - F[i][1] + F[N][2] - F[j][2]);
}
}
printf("%d\n", N*M - ans);
}