Lessons from Sliding Window

What did you learn?

$1.$ Sliding window works for contiguous subarray/substring problems where you need to find an optimal window satisfying some constraint.

$2.$ Fixed windows slide one position at a time. Variable windows expand and shrink based on conditions.

$3.$ Each element is processed at most twice (once added, once removed). You get $O(n)$ time despite nested loops. Look for keywords: "contiguous," "subarray," "substring," "window of size k."