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>
  #include <stdlib.h>
  #include <string.h>
  int main() {
    int rep=0;
    int pos=1;
    char tab[5];
    int occ[26]={0};
    scanf("%s",tab);
    for (int i = 0; i <4; i++) {
    occ[tab[i]-'A']++;
    }
    for (int i = 0; i < 26; i++) {
      if (occ[i]!=0) {
        rep++;
      }
    }
    if (rep!=2) {
      printf("NO\n");
    }
    else
    printf("YES\n");
    return 0;
  }