leetcode/work/1/Easy/String/20.valid-parentheses.py

"""
20. Valid Parentheses
Difficulty: Easy
https://leetcode.com/problems/valid-parentheses/

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Given a string s containing just the characters '(', ')', '{', '}',
'[' and ']', determine if the input string is valid.

An input string is valid if:

        • Open brackets must be closed by the same type of brackets.

        • Open brackets must be closed in the correct order.

• 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 <= 10^4

        • s consists of parentheses only '()[]{}'.
"""


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

        for c in s:
            if c in pairs:
                if stack and pairs[c] == stack[-1]:
                    stack.pop()
                else:
                    return False
            else:
                stack.append(c)

        return True if not stack else False