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Given an array of integers and an integer **k**, you need to find the number of **unique** k-diff pairs in the array. Here a **k-diff** pair is defined as an integer pair (i, j), where **i** and **j** are both numbers in the array and their absolute difference is **k**.

**Example 1:**

Input:[3, 1, 4, 1, 5], k = 2Output:2Explanation:There are two 2-diff pairs in the array, (1, 3) and (3, 5).

Although we have two 1s in the input, we should only return the number ofuniquepairs.

**Example 2:**

Input:[1, 2, 3, 4, 5], k = 1Output:4Explanation:There are four 1-diff pairs in the array, (1, 2), (2, 3), (3, 4) and (4, 5).

**Example 3:**

Input:[1, 3, 1, 5, 4], k = 0Output:1Explanation:There is one 0-diff pair in the array, (1, 1).

**Note:**

- The pairs (i, j) and (j, i) count as the same pair.
- The length of the array won't exceed 10,000.
- All the integers in the given input belong to the range: [-1e7, 1e7].

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