Greatest English Letter in Upper and Lower Case LeetCode solution in Python

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# Runtime: 34 ms (Top 92.91%) | Memory: 13.8 MB (Top 66.80%)
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class Solution:
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    def greatestLetter(self, s: str) -> str:
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        cnt = Counter(s)
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        return next(
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            (u for u in reversed(ascii_uppercase) if cnt[u] and cnt[u.lower()]), ""
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        )