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October 1Easy

Valid parentheses

  • Stack
  • Bracket Sequences

Problem

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. 3. Every close bracket has a corresponding open bracket of the same type.

Solution

class Solution:
    def isValid(self, s: str) -> bool:
        stack = []
        pairs = {")": "(", "]": "[", "}": "{"}
        for char in s:
            if char not in pairs:
                stack.append(char)
            else:
                if not stack or pairs[char] != stack.pop():
                    return False

        return not stack