6 articles
LeetCode 239 — asked at Amazon, Google, and Microsoft. Find the maximum in each sliding window of size k in O(n) using a monotonic decreasing deque. The deque stores indices in decreasing order of value — pop from front when out of window, pop from back when current element is larger.
Negative numbers completely break the classic sliding window for minimum-length subarray problems. Learn exactly why, then master the only correct approach — a monotonic deque on prefix sums — with a step-by-step visual trace, the three mistakes every candidate makes, and every real interview follow-up with approach hints.
LeetCode 239 Sliding Window Maximum is a Google classic that returns the max of every length-k window. The optimal answer maintains a monotonic decreasing deque of indices for amortised O(n) time.
Find the maximum in every sliding window of size k using a monotonic decreasing deque that maintains candidate indices in O(n) total time. The hardest and most elegant deque problem — mastering this unlocks Shortest Subarray with Sum At Least K and Jump Game VI.
Find the maximum in every sliding window of size k in O(n) using a monotonic decreasing deque of indices — the classic hard problem that separates senior engineers from the rest.
Find the shortest subarray whose sum is at least k, even with negative numbers, using a monotone increasing deque on prefix sums — the canonical hard problem where a simple sliding window fails.