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 Scala (2.11.7) (judge verdict: Accepted)

object Main extends App {
  val S = io.StdIn.readLine()
  val map = scala.collection.mutable.Map.empty[String, Int]
  S.foreach { char =>
    val charStr = char.toString
    if (map.contains(charStr)) {
      val count = map(charStr)
      map.put(charStr, count + 1)
    } else {
      map.put(charStr, 1)
    }
  }

  val keysSize = map.keys.size

  if (keysSize == 2 && map.values.forall(_ == 2)) println("Yes")
  else println("No")
}