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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Arrays;
import java.util.Scanner;


public class Main {

    public static void main(String[] args) {
      
         Scanner entrada=new Scanner(System.in);
         int count=0;
         String S=entrada.next();
        int [] x =new int[4];
        
        
       
        for (int i = 0; i <4; i++) {
            x[i]=S.charAt(i);
            
        }
        
        Arrays.sort(x);
        for (int i = 0; i < 3; i++) {
            if(x[i]==x[i+1]){
                count++;
            }
            
        }
       
        if(x[0]==x[1]&&x[2]==x[3]&& count!=3){
            System.out.println("Yes");
        }else if(count==3 || (x[0]!=x[1]&&x[2]!=x[3])||(x[0]==x[1]&&x[2]!=x[3]) ||x[0]!=x[1]&&x[2]==x[3]  ){
            System.out.println("No");
        }
        
    }
    
}