I knew sliding window was the right move pretty quickly, but fumbled a bit on when to shrink the window versus when to record the answer.
Use a sliding window (two-pointer) technique to maintain a window that contains at most k distinct integers, expanding the right pointer and shrinking the left pointer to find the shortest valid subarray. Track the frequency of each integer in the window and the number of distinct integers to efficiently update the window.
Pro tip: Clarify edge cases upfront, such as when k is greater than the total distinct integers in the array, and mention that the sliding window approach runs in O(n) time and O(k) space, which is optimal for this problem.
Restate the problem to ensure clarity: find the minimum length of a contiguous subarray with at least k distinct integers. Discuss edge cases like empty array, k <= 0, or k > total distinct integers.
Explain that a brute-force solution would be O(n^2), but a sliding window can achieve O(n) by maintaining a window with a dynamic size and a frequency map.
Use a hash map to count frequencies of elements in the current window, and two pointers (left and right) starting at 0. Also maintain a variable for the number of distinct integers in the window.
Move the right pointer to include new elements, updating the frequency map and distinct count. When the distinct count reaches k, update the minimum length and move the left pointer to shrink the window while maintaining at least k distinct integers.
After traversing the array, return the minimum length found, or -1 if no valid subarray exists.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.