Longest Valid Parentheses LeetCode solution in Python

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# Runtime: 74 ms (Top 48.14%) | Memory: 14.8 MB (Top 24.60%)
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class Solution:
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    def longestValidParentheses(self, s: str) -> int:
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        maxi = 0
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        stack = [-1]
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        for i in range(len(s)):
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            if s[i] == "(":
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                stack.append(i)
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            else:
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                stack.pop()
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                if len(stack) == 0:
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                    stack.append(i)
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                else:
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                    maxi = max(maxi, i - stack[-1])
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        return maxi