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

As TheVillageIdiot said, it's fine. You could also implement it recursively, which might be more elegant, or might not. Finally, you might want to require that matching parentheses contain something valid between them, so as to allow "(a)" but not "()".