You are given an integer array nums and an integer k. Your task is to return the number of good subarrays of nums.

A good subarray is a contiguous subarray that contains exactly k distinct integers. For example, in the array $[1, 2, 3, 1, 2]$, the subarray $[1, 2, 3]$contains $3$ distinct integers: $1$, $2$, and $3$ ...