Leetcode - Valid Parentheses Solution

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.
2. Open brackets must be closed in the correct order.

Example 1:

Input: s = "()"
Output: true

Example 2:

Input: s = "()[]{}"
Output: true

Example 3:

Input: s = "(]"
Output: false

Example 4:

Input: s = "([)]"
Output: false

Example 5:

Input: s = "{[]}"
Output: true

Constraints:

• 1 <= s.length <= 104
• s consists of parentheses only '()[]{}'.

Solution in Python

import re
class Solution:
    def isValid(self, s: str) -> bool:
        bracket_map = {"(": ")", "[": "]",  "{": "}"}
        open_par = set(["(", "[", "{"])
        stack = []
        for i in s:
            if i in open_par:
                stack.append(i)
            elif stack and i == bracket_map[stack[-1]]:
                stack.pop()
            else:
                return False
        return stack == []