Problem:
Score : 100 points

Problem Statement

You are given a 4-character string S consisting of uppercase English letters.
Determine if S consists of exactly two kinds of characters which both appear twice in S.

Constraints

The length of S is 4.

S consists of uppercase English letters.

Input

Input is given from Standard Input in the following format:

S

Output

If S consists of exactly two kinds of characters which both appear twice in S, print Yes; otherwise, print No.

Sample Input 1

ASSA

Sample Output 1

Yes

S consists of A and S which both appear twice in S.

Sample Input 2

STOP

Sample Output 2

No

Sample Input 3

FFEE

Sample Output 3

Yes

Sample Input 4

FREE

Sample Output 4

No

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
    
using namespace std;

int main() {
    
    ios::sync_with_stdio(false);
    
    string s; cin >> s;
    vector<int> alfabeto(26, 0);

    for (char c : s) {
        alfabeto[(int)c - 65] = 1;
    }

    int total = 0;
    for (int i = 0; i < alfabeto.size(); i++) {
        if (alfabeto[i] != 0) {
            total++;
        }
    }

    if (total == 2) {
        cout << "YES" << endl;
    }
    else {
        cout << "NO" << endl;
    }

    return 0;
}