[BOJ] 3986번 좋은 단어

#include <iostream>
#include <stack>
#include <string>
using namespace std;
stack <char> s;
string str;
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    int n;
    int result = 0;
    char ch;
    cin >> n;
    for (int i = 0; i < n; i++) {
        cin >> str;
        int cnt = 0;
        s.push(str[0]);
        while (1) {
            cnt++;
            if (str[cnt] == 'A' || str[cnt] == 'B') {
                if (!s.empty()) {
                    if (s.top() == str[cnt]) s.pop();
                    else s.push(str[cnt]);
                }
                else s.push(str[cnt]);
            }
            else break;
        }
        if (!s.empty()) while (!s.empty()) s.pop();
        else result += 1;
    }
    cout << result << '\n';
    return 0;
}