Checking string has balanced parentheses

Question

I am reading the Algorithm Design Manual Second Edition and this is from an exercise question. Quoting the question

A common problem for comp

Answer 1

I think this is the intention, but really you just need to decrement and increment a counter if you are only dealing with parenthesis. If you are dealing with the pairings of square brackets, angle brackets, curly braces or whatever character pairing you'd like to use, you'll need a stack like you have done.

You can also use a list, pulling the head element off and on, but really a stack is probably implemented as a list anyway --at least it is in ocaml.