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0239-sliding-window-maximum.adoc

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239. Sliding Window Maximum

{leetcode}/problems/sliding-window-maximum/[LeetCode - Sliding Window Maximum^]

Given an array nums, there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Return the max sliding window.

Example:
Input: nums = [1,3,-1,-3,5,3,6,7], and k = 3
Output: [3,3,5,5,6,7]
Explanation:

Window position                Max
---------------               -----
[1  3  -1] -3  5  3  6  7       3
 1 [3  -1  -3] 5  3  6  7       3
 1  3 [-1  -3  5] 3  6  7       5
 1  3  -1 [-3  5  3] 6  7       5
 1  3  -1  -3 [5  3  6] 7       6
 1  3  -1  -3  5 [3  6  7]      7

Note:

You may assume k is always valid, 1 ≤ k ≤ input array’s size for non-empty array.

Follow up:

Could you solve it in linear time?

思路分析

最佳解决方案是单调栈：下面最大，单调递增。

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使用单调栈，即使数组最大元素在最前面也没事，可以通过判断栈的长度，超过指定长度则将第一个元素删除，那么第一个元素就是当前窗口的最大值。

一刷
link:{sourcedir}/_0239_SlidingWindowMaximum.java[role=include]
二刷
link:{sourcedir}/_0239_SlidingWindowMaximum_2.java[role=include]

思考题

思考一下动态规划解法的正确性！