Question is:

Write efficient Java code using Hashset or HashMap to solve and estimate the run-time complexity.

Given an array of integers, and given a specific value k (not equal to 0), produce all unique pairs of values in the array which differ by k. For example, if the array has [1,4,9,12, 6, 15, 5, 13,17] and k=3, the answer would be (1,4 ) ( 9,12), ( 9,6), (12,15). If k=4, the answer would be (1,5), (9,5), (13,17),(9,13). public void differByK(int[] arr, int k)