Count pairs with absolute difference equal to k

Given an array and a positive integer k, the task is to count pairs (i, j) such that the absolute difference between arr[i] and arr[j] equals k. The solution can be implemented using a naive O(n^2) approach or an optimized O(n) approach using a hash map. The hash map approach tracks the frequency of elements and checks for the presence of complementary values. The result is the total number of such pairs. 

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