Given an integer array nums and an integer k, return the number of unique pairs of values (a, b) such that a and b both appear in nums and |a - b| = k.

A pair is considered unique based on its values, not on the indices where those values occur in nums.

Note: When k = 0, a valid pair requires a value to appear at least twice in nums.

Constraints:

• $1 \leq$ nums.length $\leq 10^4$

• $-10^7 \leq$ nums[i] $\leq 10^7$

• $0 \leq$ k $\leq 10^7$

Input: nums = [8, 12, 16, 4, 4, 20]-List[int], k = 4-int
Output: 4-int
Explanation: The unique value pairs with difference 4 are (4,8), (8,12), (12,16), and (16,20). The duplicate 4 does not create any additional unique pairs.

Input: nums = [0, 0, 0, 1, 2, 3]-List[int], k = 0-int
Output: 1-int
Explanation: When k = 0, we count values that appear at least twice. Only the value 0 repeats, so the only valid pair is (0,0).

Input: nums = [-10, -7, -4, -1, 2, 5, 8]-List[int], k = 3-int
Output: 6-int
Explanation: The unique pairs with difference 3 are (-10,-7), (-7,-4), (-4,-1), (-1,2), (2,5), and (5,8).

Input: nums = [10000000, -10000000, 0, 9999999, -9999999]-List[int], k = 10000000-int
Output: 2-int
Explanation: The unique pairs with difference 10,000,000 are (-10000000,0) and (0,10000000). The values 9999999 and -9999999 do not form any additional pair with difference 10,000,000.

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