The sliding window part clicked pretty fast.
Use a sliding window (two pointers) to maintain a subarray where the difference between the maximum and minimum elements is at most the limit. Efficiently track the max and min within the window using monotonic deques, expanding the right pointer and shrinking the left when the condition is violated. Keep track of the maximum window length seen.
Pro tip: Mention that the monotonic deque approach gives O(n) time, which is optimal, and briefly compare it to the O(n log n) multiset approach to show awareness of trade-offs. Also, clarify that the condition 'absolute difference between any two elements' is equivalent to max - min <= limit.
Confirm that the subarray must be contiguous and that the condition applies to all pairs, which simplifies to max - min <= limit. Ask about input size to determine if O(n) is necessary.
Use two monotonic deques: one for maintaining the maximum (decreasing order) and one for the minimum (increasing order) in the current window. This allows O(1) amortized access to the max and min.
Initialize left = 0, maxLen = 0. Iterate right from 0 to n-1, updating the deques. While max - min > limit, increment left and remove elements from deques if they fall out of the window. Update maxLen with the current window size.
Explain that each element is added and removed from each deque at most once, giving O(n) time and O(n) space. Discuss edge cases like empty array, limit = 0, or all elements equal.
Walk through a small example to verify correctness, then summarize the approach and its efficiency. Mention alternative approaches (e.g., multiset) and why the deque method is preferred.
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