20 Valid Parentheses

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 '()[]{}'.
Python
Golang
Runtime
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class Solution:
    def isValid(self, s: str) -> bool:
        stack = []
        mapping = {')': '(', '}': '{', ']': '['}
        for c in s:
            if c in mapping:
                if not stack or stack[-1] != mapping[c]:
                    return False
                stack.pop()
            else:
                stack.append(c)
        return not stack