The Subarray Problem

New problem type: find some property of contiguous subarrays. Maybe the maximum sum, or the longest with distinct elements, or the shortest with sum at least $k$.

Brute force: enumerate all subarrays. There are $O(n^2)$ of them, and processing each takes $O(n)$. That's $O(n^3)$. Sliding window reduces this to $O(n)$ for many problems.