20 Valid Parentheses - Easy

Problem:

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 '()[]{}'.

Problem Analysis:

• use stack
• O(n) time

Solutions:

class Solution:
    def isValid(self, s: str) -> bool:
        if not
        stack = []
        closeToOpen = {")":"(", "]": "[", "}":"{"}

        for c in s:
            print(stack)
            if c in closeToOpen:
                if stack and stack[-1] == closeToOpen[c]:
                    stack.pop()
                else:
                    return False
            else:
                stack.append(c)
        return True if not stack else False

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