gistfile1.txt

package gtan

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 succ(n: String): String = {
    n match {
      case "" => ""
      case _ =>
        val calc = n.foldRight(("1", "")) { (ch, result) =>
          val ddd = result match {
            case ("", _) => ("", ch.toString)
            case _ => ch match {
              case x if (x >= '0' && x < '9' || x >= 'a' && x < 'z' || x >= 'A' && x < 'Z') =>
                ("", (ch + 1).toChar.toString)
              case '9' => ("1", "0")
              case 'z' => ("a", "a")
              case 'Z' => ("A", "A")
              case _ => ("", "?") // should not happen
            }
          }
          (ddd._1, ddd._2 + result._2)
        }
        calc._1 + calc._2
    }
  }

}