Leetcode 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.
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

Constraints:

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

The problem is simple, just find if the coming parenthese matches with the lastest element in the stack.

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

        for parenthese in s:
            if not stack:
                stack.append(parenthese)
            elif stack[-1] == match_dict.get(parenthese):
                stack.pop()
            else:
                stack.append(parenthese)
        
        return len(stack) == 0