/**
    * Exercise 2
    */
  def balance(chars: List[Char]): Boolean = {

    def balanceInner(chars: List[Char], acc: Int = 0): Boolean = {
      def accUpgrade(character: Char) = character match {
        case '(' => acc + 1
        case ')' => acc + -1
        case _ => acc
      }

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

    balanceInner(chars)
  }