Longest Arithmetic Subsequence of Given Difference LeetCode solution in Python

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# Runtime: 548 ms (Top 98.07%) | Memory: 27.7 MB (Top 73.31%)
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class Solution:
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    def longestSubsequence(self, arr: List[int], difference: int) -> int:
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        d = defaultdict(int)
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        for num in arr:
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            if num - difference in d:
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                d[num] = d[num - difference] + 1
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            else:
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                d[num] = 1
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        return max((d[x] for x in d))