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.List;
import java.util.Scanner;
import java.util.function.Function;
import java.util.stream.Collectors;

public class Main {

    public static void main(String[] args) {
        Scanner stdin = new Scanner(System.in);
        List<Long> s = stdin.nextLine()
                            .chars()
                            .boxed()
                            .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()))
                            .values()
                            .stream()
                            .collect(Collectors.toList());
        String ans = s.equals(Arrays.asList(2L, 2L)) ? "Yes" : "No";
        System.out.println(ans);
    }

}