Interview Q&A / Data Structures & Algorithms

1. How do you find the longest substring without repeating characters?

   Use a sliding window. Expand the right end one character at a time and remember the last index where each character was seen. If the new character already appears inside the window, move the left end just past its previous position. Track the largest window size. This is O(n) time.

   AdvancedIn-depthCoding4 min read
2. How do you find the maximum in every sliding window of size k?

   Keep a deque of indices whose values are in decreasing order. Drop indices that left the window from the front, drop smaller values from the back before adding the new index, and the front is always the window maximum.

   AdvancedQuick answerCoding1 min read