LeetCode · Sliding Window
Sliding Window Problem Set
Fixed and variable-size windows over sequences. The key insight: expand right, shrink left, track state in a map or counter.
Concept page: Sliding Window
| Difficulty | Pattern | Problem | Key Insight |
|---|---|---|---|
| Easy | fixed | LC 121 · Best Time to Buy and Sell Stock | Track min price so far, max profit at each step. O(n). |
| Easy | fixed | LC 643 · Maximum Average Subarray I | Fixed-size window of length k. Update sum in O(1) per slide. |
| Medium | variable | LC 3 · Longest Substring Without Repeating Characters | Expand right, shrink left on duplicate. HashMap or HashSet. O(n). |
| Medium | variable | LC 209 · Minimum Size Subarray Sum | Shrink when sum reaches the target to minimize the window. O(n). |
| Medium | variable | LC 424 · Longest Repeating Character Replacement | Window size − max freq ≤ k. Expand right, shrink left. O(n). |
| Medium | fixed | LC 438 · Find All Anagrams in a String | Fixed-size window, frequency match. O(n). |
| Medium | variable | LC 567 · Permutation in String | Fixed-size window with frequency comparison. O(n). |
| Medium | variable | LC 904 · Fruit Into Baskets | At most 2 distinct elements → longest subarray. O(n). |
| Medium | variable | LC 1004 · Max Consecutive Ones III | Track zero count and keep the longest window with at most k zeroes. O(n). |
| Hard | variable | LC 76 · Minimum Window Substring | Expand to cover all chars, shrink to minimise. O(n). |
| Hard | monotonic | LC 239 · Sliding Window Maximum | Monotonic deque tracks max in fixed window. O(n). |