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.*;

public class Main{
	public static void main(String args[]) {

		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		HashMap<Character, Integer> hm = new HashMap<>();
		char ch=' ';
		for(int i = 0; i < 4; i++) {
			ch = S.charAt(i);
			if(!hm.containsKey(ch)) {
				hm.put(ch, 1);
			}
			else {
				hm.put(ch, hm.get(ch) + 1);
			}
		}
		System.out.println((hm.size() == 2 && hm.get(ch) == 2)?"Yes":"No");
	}
}