LeetCode 20 - Valid Parentheses Problem

Problem Statement

Given a string 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.

Note that an empty string is also considered valid.

Example 1:

Input: "()"
Output: true

Example 2:

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

Example 3:

Input: "(]"
Output: false

Example 4:

Input: "([)]"
Output: false

Example 5:

Input: "{[]}"
Output: true

Solution:

class Solution: def isValid(self, s: str) -> bool: if not s: return True matches = {']': '[', '}': '{', ')':'('} stack = [] for char in s: if char in matches.values(): stack.append(char) elif char in matches.keys(): if len(stack)==0 or stack[-1]!=matches[char]: return False stack.pop() return len(stack)==0