Test Succ

Succ.scala

object Succ {

  def main(args: Array[String]) {
    assert(succ("") == "")
    assert(succ("3") == "4")
    assert(succ("R2D3") == "R2D4")
    assert(succ("R293") == "R294")
    assert(succ("R2D9") == "R2E0")
    assert(succ("A99") == "B00")
    assert(succ("Z99") == "AA00")
    assert(succ("Zz99") == "AAa00")
    assert(succ("9Z") == "10A")
    println("finished")
  }

  def apply(s : String, index : Int, firstCh : String) : String = {
    if(index <0) firstCh + s else {
      s.apply(index) match {
        case 'z' => apply(s.updated(index, 'a'), index -1, "a");
        case 'Z' => apply(s.updated(index, 'A'), index -1, "A");
        case '9' => apply(s.updated(index, '0'), index -1, "1");
        case _ => s.updated(index, (s.apply(index) + 1).toChar);
      }
    }
  }

  def succ(s:String): String = if(s.isEmpty) "" else apply(s, s.length()-1, "");
}