Subarrays with K Different Integers

Hard

Given an integer array nums and an integer target (= k), return the number of contiguous subarrays that contain exactly target distinct integers.

Example 1

Input:  nums = [1,2,1,2,3], target = 2
Output: 7

Example 2

Input:  nums = [1,2,1,3,4], target = 3
Output: 3

Constraints

• 1 <= nums.length <= 2*10^4
• 1 <= nums[i] <= nums.length
• 1 <= target <= nums.length