Sliding Window Technique

The sliding window technique avoids redundant calculations by keeping track of a subset of elements (the "window") as it moves across an array or string.

📊 How it works

Window of size K = 3:
┌───┬───┬───┐───┬───┬───┬───┐
│ 2 │ 1 │ 5 │ 1 │ 3 │ 2 │ 9 │   -> Sum = 8
└───┴───┴───┘───┴───┴───┴───┘

Slide right: Subtract left (2), Add new right (1)
┌───┌───┬───┬───┐───┬───┬───┐
│ 2 │ 1 │ 5 │ 1 │ 3 │ 2 │ 9 │   -> Sum = 7
└───└───┴───┴───┘───┴───┴───┘

• Define the Window: Maintain a start and end boundary.
• Slide: Shift the window to the right by adding the next element and removing the leftmost element.
• Time Complexity: Reduces time complexity from O(N * K) to O(N).

When to use? Ideal for problems involving contiguous subarrays or substrings (e.g., finding the maximum sum of K consecutive elements, or longest substring with unique characters).