Shortest Subarray with at Least K Distinct Values

Given an array `nums` of positive integers and an integer `k`, call a contiguous subarray **good** when it contains at least `k` distinct values. Implement: ```text min_good_subarray_length(nums: List[int], k: int) -> int ``` Return the minimum length of a good subarray. Return `-1` if no good subarray exists. ### Constraints - `1 <= len(nums) <= 200_000` - `1 <= nums[i] <= 10^9` - `1 <= k <= 200_000` - The target complexity is (O(n)) expected time and (O(d)) extra space, where (d) is the number of distinct values in the active window. ### Clarifications - The subarray must be contiguous. - “At least `k`” permits more than `k` distinct values. - Repeated occurrences count once toward the distinct-value total. ```hint Shrink every valid window Advance one boundary until the window becomes good, then move the other boundary as far as possible while it remains good. ``` ### Examples ```text Input: nums = [1, 2, 2, 3, 1], k = 3 Output: 3 Explanation: [2, 3, 1] has three distinct values. Input: nums = [5, 5, 5], k = 2 Output: -1 ``` ### Evaluation Focus - Correct maintenance of frequency and distinct-value counts. - Minimality across overlapping candidate windows. - Linear two-pointer behavior without restarting a scan for every left endpoint. ### Extension How would you count all subarrays containing at least `k` distinct values?