Checking for Valid Parentheses

November 15, 2017

Tags: programming

A quick writeup on how to check if a string has valid parentheses. The easiest way to implement this is with a stack. In python, we use a list as a stack (append() behaves like push()):

checkParentheses.py

class CheckParentheses(object):
    def checkValidAmount(self, s):
        if s.count('(') != s.count(')') or s.count('{') != s.count('}') or s.count('[') != s.count(']'):
            return False
        return True
    
    def isValid(self, s):
        if not self.checkValidAmount(s):
            return False
        
        stack = []
        d = {')' : '(', '}': '{', ']': '['}
        for c in s:
            if c in ['(', '{', '[']:
                stack.append(c)
            else:
                res = stack.pop()
                if d[c] != res:
                    return False
        
        return True