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.Scanner;
import java.util.Arrays;
class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String str = sc.next();

        int[] A = new int[4];
        for (int i = 0; i < 4; i++) {
            A[i] = str.charAt(i);
        }
        Arrays.sort(A);

        if (A[0] == A[1] && A[2] == A[3] && A[0] != A[3]) {
            System.out.println("Yes");
        } else { 
            System.out.println("No");
        }
    }
}