Subarrays with K Different Integers

Problem Return the number of contiguous subarrays containing exactly k distinct integers.

Input / Output

• Input: int array nums, int k. Output: count of subarrays.

Constraints

• n up to 2*10^4; O(n) expected — direct exact-k windowing is awkward, which is the trap.

Example

• nums = [1,2,1,2,3], k = 2 → 7; nums = [1,2,1,3,4], k = 3 → 3.