Given an integer array `nums` and an integer `k`, return the number of good subarrays of `nums`.

A good array is an array where the number of different integers in that array is exactly `k`.

- For example, `[1,2,3,1,2]` has `3` different integers: `1`, `2`, and `3`.

A subarray is a contiguous part of an array.

Example 1:

    Input: nums = [1,2,1,2,3], k = 2
    Output: 7
    Explanation: Subarrays formed with exactly 2 different integers: [1,2], [2,1], [1,2], [2,3], [1,2,1], [2,1,2], [1,2,1,2]

Example 2:

    Input: nums = [1,2,1,3,4], k = 3
    Output: 3
    Explanation: Subarrays formed with exactly 3 different integers: [1,2,1,3], [2,1,3], [1,3,4].

Constraints:

- `1 <= nums.length <= 2 * 104`
- `1 <= nums[i], k <= nums.length`