Lesson 186
Sliding Window
Fixed · Variable · Two Pointers
1:00Slide a window of contiguous elements across an array or string, reusing the overlap to reduce O(n·k) or O(n²) brute force down to O(n).
By the end, you can
- Explain why a sliding window achieves O(n) while a brute-force window scan costs O(n·k) or O(n²).
- Implement the fixed-size sliding window for max sum of k consecutive elements, correctly computing the first window and updating with enter/leave.
- Implement the variable-size sliding window for longest substring under a constraint, including zero-count key deletion.
- Choose between a fixed and variable window given a problem statement.
- Apply the `n - k + 1` formula to count fixed windows and the `right - left + 1` formula for window length.
- Identify when sliding window does not apply (non-contiguous selections).
- Analyze the amortized O(n) time and O(1)/O(k) space complexity of a sliding window solution.
Up next in Coding Interview Patterns
