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 '()[]{}'.

class Solution(object):
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        left = ["(", "{", "["]
        brackets = ["()", "{}", "[]"]
        stack = []
        
        
        for c in s:
            if len(stack) == 0 or c in left:
                stack.append(c)
            elif stack[-1] + c in brackets:
                stack.pop()
            else:
                return False
        
        if len(stack) == 0:
            return True
        else:
            return False
        

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