Problems

Parentheses Balancing Check

• Use a stack for parenthesis storage

• Push in case of an opening one

• Pop in case of a closed one but only when the stack is not empty and the head is an opening one

• Run through until the end, balanced if stack is empty

• Use empty list for an early exit

  // Scala
  def balance(chars: List[Char]): Boolean = {
    def _balance(list: List[Char], stack: List[Char]): Boolean = {
      list match {
        case Nil => stack.isEmpty
        case '(' :: cs => _balance(cs, '(' :: stack)
        case ')' :: cs => if (!stack.isEmpty && stack.head == '(') _balance(cs, stack.tail) else _balance(Nil, ')' :: stack)
        case _ :: cs => _balance(cs, stack)
      }
    }
   
    _balance(chars, Nil)
  }