Minimum Number of Swaps to Make the String Balanced LeetCode solution in Python

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class Solution:
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    def minSwaps(self, s: str) -> int:
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        res, bal = 0, 0
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        for ch in s:
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            bal += 1 if ch == "[" else -1
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            if bal == -1:
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                res += 1
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                bal = 1
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        return res