K-diff Pairs in an Array LeetCode solution in Python

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class Solution:
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    def findPairs(self, nums: List[int], k: int) -> int:
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        if k < 0:
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            return 0
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        # initialize hash table
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        freq = {}
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        for num in nums:
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            freq[num] = freq.get(num, 0) + 1
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        # iterate through array and find pairs
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        count = 0
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        for num in freq:
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            if k == 0:
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                if freq[num] > 1:
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                    count += 1
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            else:
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                if num + k in freq:
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                    count += 1
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        # return count of unique pairs
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        return count