20. Valid Parentheses

#link to problem https://leetcode.com/problems/valid-parentheses/description/

class Solution(object):
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        check if empty or odd (can't pass)
        loop through string
        have dict of key value pairs for closed brackets to open brackets
        have list of closed brackets
        have list to represent stack
        check if bracket is open, if so add it to stack
        else check if stack is non-empty and last element is a match
        if so return true, else return false 
        once done if stack is empty return true
        """
        if len(s) == 0 or len(s) % 2 != 0:
            return False
        bracket_dict = {')':'(', ']':'[','}':'{'}
        closed_brackets = [')',']','}']
        stack = []
        for bracket in s:
            #check if bracket is open
            if bracket not in closed_brackets:
                stack.append(bracket)
            else:
                try:
                #if you can't access stack[-1], must be invalid
                    if bracket_dict[bracket] == stack[-1]:
                        stack.pop()
                    else:
                        return False
                except:
                    return False
        #stack must be empty to pass
        return len(stack) == 0