Please solve the programming task below using a self-contained code snippet in a markdown code block.

Given an array of integers nums and an integer k, return the number of unique k-diff pairs in the array.
A k-diff pair is an integer pair (nums[i], nums[j]), where the following are true:

0 <= i, j < nums.length
i != j
|nums[i] - nums[j]| == k

Notice that |val| denotes the absolute value of val.
 
Please complete the following python code precisely:
```python
class Solution:
    def findPairs(self, nums: List[int], k: int) -> int:
```