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Leetcode - Valid Parentheses Solution

Poor Man
Published
Updated
Reading time
1 min read

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:

Text
Input: s = "()"
Output: true

Example 2:

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

Example 3:

Text
Input: s = "(]"
Output: false

Example 4:

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

Example 5:

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

Constraints:

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

Solution in Python#

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 == []

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