varLenEncode.scala

import scala.annotation.tailrec

object VarLenEncoding extends App {
  val testData = List(("", ""), ("XYZ", "XYZ"), ("AAABC", "A3BC"), ("XXXX", "X4"))

  def encode(s: String): String = split(s, Nil).map(f => if (f.length == 1) f else s"${f.head}${f.length}").mkString

  def decode(s: String): String = ???

  @tailrec def split(s: String, acc: List[String]): List[String] = {
    if (s.isEmpty) Nil
    else {
      val start: Char = s(0)
      val bucket = s.takeWhile(p => p == start)
      if (s.length - bucket.length == 0) acc ++ List(bucket)
      else split(s.substring(bucket.length), acc ++ List(bucket))
    }
  }

  testData.foreach { t =>
    println(s"encoded: ${encode(t._1)}, expected: ${t._2}")
    assert(encode(t._1) == t._2)
  }
}