DSA03023 - SẮP XẾP VIÊN BI

#include<iostream>
using namespace std;
#define mod 1000000007
int main() {
	int n; cin >> n;
	string s; cin >> s;
	int x=0, t=0, d=0;
	for (int i = 0; i < n; i++)
		if (s[i] == 'X')x++;
		else if (s[i] == 'T')t++;
		else d++;
	int dem = 0;
	for (int i = n - d; i < n; i++)
		if (s[i] != 'D')dem++;
	for (int i = 0; i < x; i++)
		if (s[i] != 'X')dem++;
	int a = 0, b = 0;
	for (int i = n - d; i < n; i++)
		if (s[i] == 'X')a++;
	for (int i = 0; i < x; i++)
		if (s[i] == 'D')b++;
	cout << dem - min(a, b) << endl;
}