ソースコード
#include "iostream"
#include "climits"
#include "list"
#include "queue"
#include "stack"
#include "set"
#include "functional"
#include "algorithm"
#include "math.h"
#include "utility"
#include "string"
#include "map"
#include "unordered_map"
#include "iomanip"
#include "random"
using namespace std;
const long long int MOD = 1000000007;
long long int power(long long int x, long long int n, long long int M) {
long long int tmp = 1;
if (n > 0) {
tmp = power(x, n / 2, M);
if (n % 2 == 0) tmp = (tmp*tmp) % M;
else tmp = (((tmp*tmp) % M)*x) % M;
}
return tmp;
}
long long int N, M, K, Q, W, H, L, R;
long long int ans;
int main() {
ios::sync_with_stdio(false);
string s[100];
int b[100] = {};
int r[100] = {};
int w[100] = {};
cin >> H >> W;
for (int i = 0; i < H; i++)cin >> s[i];
for (int i = 0; i < H; i++) {
for (auto j : s[i]) {
if (j == 'W')w[i]++;
if (j == 'R')r[i]++;
if (j == 'B')b[i]++;
}
w[i + 1] = w[i];
r[i + 1] = r[i];
b[i + 1] = b[i];
}
//cout << w[H] << " " << r[H] << " " << b[H] << endl;
ans = 100000;
for (int i = 0; i < H; i++) {
for (int j = i + 1; j < H-1; j++) {
ans = min(ans, (i + 1)*W - w[i] + (j - i)*W - b[j] + b[i] + (H - j - 1)*W - r[H] + r[j]);
}
}
cout << ans << endl;
return 0;
}