def balance(chars: List[Char]): Boolean = {
  def innerBalance(chars: List[Char], summation: Int): Int = {
    if (chars.isEmpty)
      summation
    else if (chars.head == '(')
      innerBalance(chars.tail, summation + 1)
    else if (chars.head == ')')
      if (summation <= 0)
        -1
      else
        innerBalance(chars.tail, summation - 1)
     else
        innerBalance(chars.tail, summation)
  }
  if (innerBalance(chars, 0) == 0)
    true
  else false
}