def balance(chars: List[Char]): Boolean = {

    def balanceInner(chars: List[Char], acc: Int = 0): Boolean = {
      def accUpgrade(character: Char): Int =
        if (character == '(') acc + 1
        else if (character == ')') acc - 1
        else acc

      if (acc < 0 ) false
      else if (chars.isEmpty)
        if (acc == 0)true else false
      else balanceInner(chars.tail, accUpgrade(chars.head))
    }

    balanceInner(chars)
  }