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.Collections;
import java.util.List;
import java.util.Scanner;
import java.util.ArrayList;

public class Main {

    public static void main(String[] args) {
        List<Integer> l = new ArrayList<>();
        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        for (int i = 0; i < s.length(); i++) {
            int x = s.charAt(i);
            l.add(x);
        }
        Collections.sort(l);
        if (l.get(0) == l.get(1) && l.get(2) == l.get(3) && l.get(0) != l.get(3)) {
            System.out.println("Yes");
        }
        else {
            System.out.println("No");
        }
    }
}