Sliding Window

Efficiently process subarrays or substrings of a fixed or variable size.

15 problems 0 Easy 13 Medium 2 Hard

Overview

The sliding window technique maintains a window of elements that satisfies a condition, expanding or shrinking it as you traverse the data. It converts brute-force O(n²) solutions into O(n) by avoiding redundant re-computation.

When to Use

Finding max/min subarray of size k
Longest substring without repeating characters
Minimum window containing all characters
Fixed-size window statistics

Common Mistakes

Forgetting to shrink the window when the constraint is violated
Off-by-one errors on window boundaries
Not resetting window state when shrinking

Complexity

Time

O(n) — each element enters and exits the window at most once

Space

O(k) where k is the window size or alphabet size

function slidingWindow(arr, k) {
  let left = 0, result = 0;
  let windowState = {}; // track window contents

  for (let right = 0; right < arr.length; right++) {
    // Expand window: add arr[right]

    // Shrink window when constraint violated
    while (/* invalid condition */) {
      // Remove arr[left] from state
      left++;
    }

    // Update result
    result = Math.max(result, right - left + 1);
  }
  return result;
}

Problems (15)

Hide completed

Problem	Difficulty	Companies	Freq
Longest Substring Without Repeating Characters	Medium	AmazonGoogle +2	High
Minimum Window Substring	Hard	FacebookAmazon +2	High
Sliding Window Maximum	Hard	AmazonGoogle +1	Medium
Longest Repeating Character Replacement	Medium	GoogleAmazon	Medium
Permutation in String	Medium	MicrosoftAmazon	Medium
Find All Anagrams in a String	Medium	FacebookUber	Medium
Max Consecutive Ones III	Medium	GoogleAmazon	Medium
Subarray Product Less Than K	Medium	Amazon	Low
Minimum Size Subarray Sum	Medium	AmazonFacebook	Medium
Fruit Into Baskets	Medium	Google	Low
Minimum Operations to Reduce X to Zero	Medium	AmazonGoogle	Medium
Longest Subarray of 1's After Deleting One Element	Medium	AmazonGoogle +1	Medium
Count Number of Nice Subarrays	Medium	Amazon	Medium
Frequency of the Most Frequent Element	Medium	AmazonGoogle	Medium
Maximum Number of Vowels in a Substring of Given Length	Medium	AmazonBloomberg	Medium

The sliding window technique turns O(n²) brute-force substring problems into clean O(n) solutions. H…

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