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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>

int main(void)
{
    unsigned int N,K,tmp;
    scanf("%d",&N);
    unsigned short int d[N];
    for(int i=0;i<N;i++){
        scanf("%u",&d[i]);
    }
    for(int s=0;s<N-1;s++){
        for(int t=s+1;t<N;t++){
            if(d[s]>d[t]){
                tmp=d[t];
                d[t]=d[s];
                d[s]=tmp;
            }
        }
    }
    K=d[N/2]-d[N/2-1];
    printf("%d\n",K);
    return 0;
}