Minimum Insertions to Balance a Parentheses String LeetCode solution in Python

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class Solution:
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    def minInsertions(self, s: str) -> int:
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        leftbrackets = insertions = 0
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        i, n = 0, len(s)
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        while i < n:
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            if s[i] == "(":
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                leftbrackets += 1
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            elif s[i] == ")":
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                if i == n - 1 or s[i + 1] != ")":
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                    insertions += 1
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                else:
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                    i += 1
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                if not leftbrackets:
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                    insertions += 1
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                else:
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                    leftbrackets -= 1
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            i += 1
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        return leftbrackets * 2 + insertions