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:

Open brackets must be closed by the same type of brackets.
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 <= 10^4
s consists of parentheses only '()[]{}'.

Solution in python:

class Solution:
    def isValid(self, s: str) -> bool:
        stack = ['0']
        for item in s:
            # if (item in ')]}') and (stack[-1] in '([{') and (')]}'.index(item) == '([{'.index(stack[-1])):
            if (item == ')' and stack[-1] == '(') or (item == ']' and stack[-1] == '[') or (item == '}' and stack[-1] == '{'):
                stack.pop()
            else:
                stack.append(item)
        if len(stack) == 1:
            return True
        else:
            return False