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 n,m,cnt,sum = 1000001,t,f;
int a[102];
string s;
pair <int, string> p1[10001];
int main (){	
	cin >> s;
	sort(s.begin(),s.end());
	for (int i = 0; i < s.size(); i += 2){
		if (s[i] == s[0]){
			t++;
		}
		else if (s[i] == s[s.size() - 1]){
			f++;
		}
	}
	for (int i = 0; i < s.size(); i += 2){
		if (s[i] == s[i + 1]){
			cnt++;
		}
		else {
			cout << "No";
			return 0;
		}
	}
	if (t == f)
	{
		cout << "Yes";
	}
	return 0;
}