20. Valid Parentheses

String Stack

Problem - Valid Parentheses

Easy

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.

 

Example 1:

Input: s = "()"

Output: true

Example 2:

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

Output: true

Example 3:

Input: s = "(]"

Output: false

Example 4:

Input: s = "([])"

Output: true

Example 5:

Input: s = "([)]"

Output: false

 

Constraints:

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

Solutions

Python3

class Solution:
    def isValid(self, s: str) -> bool:
        stack = []
        maps = { ')': '(', '}':'{', ']':'['}

        for char in s:
            if char in maps:
                top = stack.pop() if stack else ''
                if maps[char] != top:
                    return False
            else:
                stack.append(char)
        return not stack

Submission Stats:

• Runtime: 2 ms (33.97%)
• Memory: 17.9 MB (34.29%)