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: Accepted)

#include<stdio.h>
#include<string.h>

#define ATOZ_CNT 26

int main(){
    char input[5];
    int  appear[ATOZ_CNT]={0,};
    scanf("%s",input);
    for(int i=0;i<4;i++){
        appear[input[i]-'A']+=1;
    }
    int doubleAppearCnt=0;
    for(int i=0;i<ATOZ_CNT;i++){
        if(appear[i]==2)doubleAppearCnt+=1;
    }
    if(doubleAppearCnt==2)printf("Yes\n");
    else                  printf("No\n");
    
    return 0;
}