Subarrays with K Different Integers

You are 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].

Example 3:

Input: nums = [1,2,2], k = 1

Output: 4

Explanation: Subarrays formed with exactly 1 different integers:

Constraints:

• 1 <= nums.length <= 20,000
• 1 <= nums[i], k <= nums.length