Section Recap

Fixed and variable sliding windows, plus monotonic deque for range max.

Fixed: Initialize size $k$, slide by add/remove. $O(n)$ time.

Variable: Expand right, shrink left when invalid. Each element touched once.

Patterns:

• Longest/shortest with condition → Variable
• All windows size $k$ → Fixed
• Max/Min in each window → Monotonic deque

Transforms $O(n^2)$ to $O(n)$ by reusing computation.