/**
   * Exercise 2
   */
    def balance(chars: List[Char]): Boolean = {
      def innerBalance(chars: List[Char], counter: Int) : Boolean = {
        if (counter < 0) false
        else if (chars.isEmpty) counter == 0
        else {
          innerBalance(chars.tail, counter + smth(chars.head))
        }
      }
      innerBalance(chars, 0)
  }