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: Accepted)

#include <bits/stdc++.h>

using namespace std;

int counts[128];

int main(void) {
    string s;
    char c;
    int twos = 0;

    cin >> s;
    for (int i = 0; i < 128; i++) {
        counts[i] = 0;
    }
    for (int i = 0; i < 4; i++) {
        c = s[i];
        counts[int(c)]++;
    }
    for (int i = 0; i < 128; i++) {
        if (counts[i] == 2) twos++;
    }
    if (twos == 2) {
        cout << "Yes" << endl;
    } else {
        cout << "No" << endl;
    }
    return 0;
}