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: Wrong Answer)

import java.util.Scanner;

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

    Scanner sc = new Scanner(System.in);
    String source = sc.next();

    char[] type = new char[2];

    type[0] = source.charAt(0);

    for (int sceIdx = 1; sceIdx < source.length(); sceIdx++) {
      if (source.charAt(sceIdx) != type[0]) { // 0文字目と違う?
        if (type[1] == '\0') { // 違うやつ未定?
          type[1] = source.charAt(sceIdx);
        } else {
          System.out.println("No");
          return;
        }
      }
    }
    if(type[1]=='\0'){
      System.out.println("No");
      return;
    }

    int count = 0;
    for (int sceIdx = 1; sceIdx < source.length(); sceIdx++) {
      if (source.charAt(sceIdx) == type[1]) {
        count++;
      }
    }
    if(count != 2){
      System.out.println("No");
      return;
    }
    System.out.println("Yes");
    return;
  }

}