gistfile1.scala

  private def toNum(c: Char): Int = c match {
    case 'X' => 10
    case ci if c.isDigit => c.toInt
    case _ => throw new IllegalStateException("Can't get here")
  }

  def validate(s: String): Boolean = {
    val validChars = s.filter(c => c.isDigit || c == 'X')
    if (validChars.length != 10) {
      false
    } else {
      validChars.zipWithIndex.foldLeft(0){case (sum, (c, i)) => sum + (10 - i) * toNum(c)} % 11 == 0
    }
  }