LeetCopilot

Sliding Window

Learn the sliding window technique to efficiently solve array and string problems. Master fixed-size and variable-size window patterns.

The Sliding Window technique transforms $O (N^{2})$ brute force solutions into efficient $O (N)$ algorithms by maintaining a "window" of elements and sliding it through the data structure. Master fixed-size and variable-size windows, learn when to use the pattern, and avoid common pitfalls with our comprehensive guide.

Featured Guide

Complete Guide

Sliding Window Algorithm: Complete Guide With Templates (Python/Java/JS)

The only sliding window guide you'll ever need. Templates in 3 languages, 10+ worked examples, debugging checklists, and the exact decision tree FAANG interviewers expect you to know.

22 min read

Interactive Tool

Roadmap

Sliding Window Visualizer

Master the sliding window technique through interactive visualization. Watch how the window expands, shrinks, and maintains its invariant in real-time. Step through algorithms, see state changes, and understand fixed-size, variable-size, and "at most k" patterns.

Sliding Window LeetCode Roadmap: Master the Pattern in 4 Weeks (30 Problems)

Stop practicing random LeetCode problems. This week-by-week roadmap gives you exactly which problems to solve, in what order, and why—from your first easy to interview-ready in 30 days.

Tutorials

When NOT to Use the Sliding Window Pattern (5 Cases Where It Fails)

Sliding Window is a powerful optimization, but it's not a silver bullet. Learn the 5 specific scenarios where this pattern fails and what to use instead to save your interview.

Sliding WindowLeetCode PatternAlgorithm Strategy

8 min

Sliding Window Intuition: The 3 Rules You Need (Step-by-Step)

Everyone explains the code. Nobody explains why it works. This is the mental model that made sliding window 'click' for me—and it'll work for you in 10 minutes.

Sliding WindowAlgorithmsBeginner Guide

10 min

Substring vs Subarray in Sliding Window: Why Your Code Breaks

Using the same approach for strings and arrays? That's a trap. The state you track, the bugs you'll hit, and the edge cases are completely different. Here's the cheat sheet.

Sliding WindowSubstringSubarray

6 min

Sliding Window Shrinking Bug: The 4-Line Fix That Stops Wrong Answers

Infinite loop? Output is 0? You're making the same mistake 90% of candidates make—using 'if' instead of 'while'. This checklist fixes it in under 5 minutes.

DebuggingSliding WindowCommon Bugs

8 min

Sliding Window: Is It 'right - left' or 'right - left + 1'?

Stop guessing +1 or -1 until it passes. The answer is always 'right - left + 1' for inclusive windows. Here's why, and how to never get it wrong again.

Sliding WindowOff-by-oneBugs

5 min

Fixed Window vs Dynamic Window: Which Sliding Window Technique to Use?

Not all windows are created equal. Learn the critical difference between Fixed-Size and Dynamic-Size Sliding Windows, and get the decision matrix to choose the right one instantly.

Sliding WindowFixed WindowDynamic Window

7 min

Sliding Window vs Prefix Sum: The Wrong Choice Breaks Your Solution

Both solve O(N²) brute force in O(N). Both involve subarrays. But use the wrong one on 'Subarray Sum Equals K' and you'll hit a wall. Here's the decision rule.

Sliding WindowPrefix SumAlgorithm Comparison

6 min

How to Recognize Sliding Window Problems Instantly (5 Pattern Signals)

Stop guessing algorithms. Learn the 4 keywords that scream 'Sliding Window' and the mindset checklist to confirm your intuition in seconds.

Pattern RecognitionInterview TipsSliding Window

5 min

Why Sliding Window Breaks With Negative Numbers (And the One-Line Fix)

Your window shrinks. The sum goes up. What? Negative numbers destroy the greedy logic you rely on. Here's why it fails and the prefix sum fix that always works.

Negative NumbersEdge CasesPrefix Sum

6 min

Why Sliding Window Fails on LeetCode Stock Problems (And What to Use Instead)

Best Time to Buy and Sell Stock looks like a window problem. But trying to use Sliding Window will lead you down a rabbit hole. Learn why DP or Greedy is the real answer.

Stock ProblemsDynamic ProgrammingGreedy

6 min

Sliding Window Template (Fixed + Variable) — Python/Java/JavaScript

Master the universal sliding window template across Python, Java, and JavaScript. Learn how to avoid reinventing the wheel and ship bug-free solutions faster in coding interviews.

Sliding WindowLeetCodeInterview Prep

12 min

20 Best Sliding Window Problems on LeetCode (Ranked by Learning Value)

LeetCode has 200+ sliding window problems. Most teach you nothing new. These 20, in this exact order, teach everything you need—from template basics to interview-ready.

Sliding WindowLeetCodeInterview Prep

14 min

6 Sliding Window Bugs That Break Your Solution (With Fixes)

Using 'if' instead of 'while'? Calculating size as 'right - left'? These 6 mistakes trip up 90% of candidates. Here's the debugging checklist that catches them all.

Sliding WindowDebuggingLeetCode

16 min

Sliding Window vs Two Pointers: Why They're Not the Same (Quick Decision Guide)

'Isn't sliding window just two pointers?' No—and confusing them costs you 20 minutes. Quick test: if you only care about arr[left] and arr[right], it's two pointers. Here's the full decision matrix.

Sliding WindowTwo PointersLeetCode

13 min

2D Sliding Window: The Dimension Compression Trick Explained Step by Step

Trying to slide in both dimensions at once? That's O(R²C²)—way too slow. Fix two rows, compress to 1D, run Kadane's. Here's the exact template that makes matrix problems tractable.

Sliding Window2D ArrayMatrix

15 min