Count Number of Pairs With Absolute Difference K LeetCode solution in C++

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class Solution {
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 public:
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  int countKDifference(vector<int> &nums, int k) {
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    unordered_map<int, int> freq;
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    int res = 0;
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    for (auto num : nums) {
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      res += freq[num + k] + freq[num - k];
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      freq[num]++;
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    }
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    return res;
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  }
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};