License Key Formatting LeetCode solution in Python

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# Runtime: 81 ms (Top 55.38%) | Memory: 14.3 MB (Top 86.51%)
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class Solution:
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    def licenseKeyFormatting(self, s: str, k: int) -> str:
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        new_str = s.replace("-", "")
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        res = ""
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        j = len(new_str) - 1
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        i = 0
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        while j >= 0:
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            res += new_str[j].upper()
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            i += 1
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            if i == k and j != 0:
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                res += "-"
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                i = 0
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            j -= 1
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        return res[::-1]