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 (Clang 3.8.0) (judge verdict: Time Limit Exceeded)

#include <stdio.h>
int main(){
  int n,count1,count2,ans=0;
  scanf("%d",&n);
  int d[n+1],flag[100001];
  for(int i=1;i<=n;i++){
    scanf("%d",&d[i]);
  }
  
  for(int i=1;i<=100001;i++){
    flag[i]=0;
  }
  flag[0]=1;
  
  for(int k=1;k<=100000;k++){
    count1=0;
    count2=0;
    for(int i=1;i<=n;i++){
      if(k<=d[i]){
        count1+=1;
      }else{
        count2+=1;
      }
      if(count1>n/2 || count2>n/2){
        flag[k]=1;
        break;
      }
    }
    if(flag[k]==0){
      ans+=1;
    }
    if(flag[k-1]==0 && flag[k]==1){
      break;
    }
  }
  
  printf("%d",ans);
  return 0;
}