L-Problem2.scala

import scala.annotation.tailrec
import scala.collection.JavaConverters._

// you can write to stdout for debugging purposes, e.g.
// println("this is a debug message")

object Task2Solution {
  class TransformationIterator(s: String, removable: String) extends Iterator[String] {
    var i = 0
    val remLen = removable.length
    val sLen = s.length
    shift()

    override def hasNext = i < sLen && i != -1

    override def next = {
      val transformed = s.substring(0, i) + s.substring(i + remLen, sLen)
      shift()
      transformed
    }

    private def shift(): Unit = {
      i = s.indexOfSlice(removable, i)
    }
  }

  def possibleTransformations(s: String): Iterator[String] = {
    new TransformationIterator(s, "AA") ++
      new TransformationIterator(s, "BB") ++
      new TransformationIterator(s, "CC")
  }

  @tailrec
  def transform(s: String): String = {
    val transformations = possibleTransformations(s)
    if(!transformations.hasNext)
      s
    else
      transform(transformations.next())
  }

  def solution(s: String): String = {
    transform(s)
  }
}

object Main3 extends App {
//  println(Solution.solution("ACCAABBC"))
//  println(Solution.solution("ABCBBCBA"))
  println(Task2Solution.solution("A"))
//  val longStr = "BBAACC" * 1000
//  println(Task2Solution.solution(longStr))
}