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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String s = sc.nextLine();
    Map<Character, Integer> map = new HashMap<>();
    for (char c : s.toCharArray()) {
    	if (map.containsKey(c)) {
        	map.put(c, map.get(c) + 1);
        } else {
          map.put(c, 1);
        }
    }
    
    for (char i : map.keySet()) {
    	if (map.get(i) != 2) {
        	System.out.println("No");
          	return;
        }
    }
    System.out.println("Yes");
  }
}