Given nums and a non-negative integer k, count the distinct value pairs (x, y) such that both x and y occur in nums and y - x == k. Pairs are unordered and counted once no matter how many times the values repeat. When k == 0, a pair (x, x) counts only if x occurs at least twice.
Examples
Input: nums = [3, 1, 4, 1, 5], k = 2
Output: 2
Explanation: value pairs (1, 3) and (3, 5).
Input: nums = [1, 3, 1, 5, 4], k = 0
Output: 1
Explanation: only the value 1 repeats.
Constraints
0 <= len(nums) <= 10**5,0 <= k <= 10**9- Target complexity: O(n) time.
Goals
- Count pairs by value rather than by index
- Treat k = 0 as a special case