Topic
Sliding Window interview questions
All 8 Sliding Window problems from the curated set, easiest first — a core topic for 5 of the 29 engineering roles.
- Easy
- 0
- Medium
- 7
- Hard
- 1
- Sheets
- 3
What Sliding Window is
Updated 2026-09-09A sliding window is an adjustable magnifying lens placed over a continuous segment of a sequence. Rather than recalculating metrics for every potential subsection from scratch, the window expands rightward by absorbing fresh elements and contracts leftward to expel stale entries. Only data currently framed within the window borders contributes to the active calculation.
When to reach for it
Reach for a sliding window when a question asks for the longest, shortest, or optimal contiguous subarray or substring matching a constraint. Key signals include fixed window sizes like maximum sum across k consecutive values, or dynamic criteria like finding the shortest substring holding all target characters. If the target subset must form an unbroken continuous run, window mechanics replace repetitive segment rescanning.
How to think about it
Maintain two boundary indices, left and right, defining the active interval alongside a running state accumulator. In each step, expand the right boundary to incorporate the incoming element into state totals. When current state violates the designated problem constraints, increment the left boundary while deducting departing values until validity is restored. Update your tracking metric, whether minimum window length or maximum score, only during valid intervals.
What each operation costs
| Operation | Time |
|---|---|
| slide window across full array length | O(n) |
| update running aggregate per incoming element | O(1) |
| auxiliary window frequency map storage | O(k) |
What usually goes wrong
- Shrinking the left border using an if statement instead of a while loop, allowing invalid window conditions to persist across iterations.
- Updating optimum results before validating window legality, recording illegal states that contain duplicate items or violate length requirements.
- Forgetting to decrement left element frequencies or remove empty keys from tracking maps when advancing the left boundary forward.
Every Sliding Window problem, easiest first
- Minimum Size Subarray SumMedium
- Fruit Into BasketsMedium
- Number of Substrings Containing All Three CharactersMedium
- Max Consecutive Ones IIIMedium
- Count Occurrences of AnagramMedium
- Maximum Points You Can Obtain from CardsMedium
- Longest K Unique Characters SubstringMedium
- Sliding Window Maximum (Two Pointers)Hard
Roles that need Sliding Window
If you are targeting one of these, Sliding Window sits early in your path rather than being optional.
Track Sliding Window in your role's order
Pick your target role and all 370 problems resequence to what that interview actually asks. Free.
Start freeSliding Window interview questions, answered
How many Sliding Window problems should I solve for interviews?
8 curated Sliding Window problems cover the patterns interviews repeat: 0 easy, 7 medium and 1 hard. They are drawn from 3 widely used sheets, deduplicated, and ordered easiest first.
Is Sliding Window actually asked in coding interviews?
Yes, though how much depends on the role. Sliding Window is a core topic for 5 of the 29 engineering roles tracked here, including Frontend Engineer, Full-Stack Developer, Performance Engineer. For other roles it is lower frequency and belongs later in a study plan.
Which Sliding Window problem should I start with?
Start with Minimum Size Subarray Sum (Medium). The list on this page is ordered easiest first for that reason, so working top to bottom builds the pattern before the harder variations arrive.
Other topics
Problem set and role mapping as of .