Count Unique Pairs With Difference K

Requirements

You receive an integer array numbers[] and a nonnegative integer k. Return how many distinct value pairs (a, b) drawn from numbers satisfy b - a == k.

• A distinct pair is counted only once per pair of values (a, b), even when either value occurs multiple times in the array.
• k can equal 0; for this case, count each distinct value occurring two or more times exactly once.

public static int countPair(int[] numbers, int k)

Preparation

• LC 532, "K-diff Pairs in an Array," is the standard matching problem; LC 1, "Two Sum," uses the related lookup-pattern fingerprint.