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45 lines
1.9 KiB
Markdown
Executable File
45 lines
1.9 KiB
Markdown
Executable File
# [239. Sliding Window Maximum](https://leetcode.com/problems/sliding-window-maximum/)
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## 题目
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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.
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**Example:**
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Input: nums = [1,3,-1,-3,5,3,6,7], and k = 3
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Output: [3,3,5,5,6,7]
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Explanation:
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Window position Max
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--------------- -----
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[1 3 -1] -3 5 3 6 7 3
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1 [3 -1 -3] 5 3 6 7 3
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1 3 [-1 -3 5] 3 6 7 5
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1 3 -1 [-3 5 3] 6 7 5
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1 3 -1 -3 [5 3 6] 7 6
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1 3 -1 -3 5 [3 6 7] 7
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**Note:**
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You may assume *k* is always valid, 1 ≤ k ≤ input array's size for non-empty array.
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**Follow up:**
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Could you solve it in linear time?
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## 题目大意
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给定一个数组 nums，有一个大小为 k 的滑动窗口从数组的最左侧移动到数组的最右侧。你只可以看到在滑动窗口 k 内的数字。滑动窗口每次只向右移动一位。返回滑动窗口最大值。
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## 解题思路
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- 给定一个数组和一个窗口为 K 的窗口，当窗口从数组的左边滑动到数组右边的时候，输出每次移动窗口以后，在窗口内的最大值。
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- 这道题最暴力的方法就是 2 层循环，时间复杂度 O(n * K)。
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- 另一种思路是用优先队列，每次窗口以后的时候都向优先队列里面新增一个节点，并删除一个节点。时间复杂度是 O(n * log n)
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- 最优的解法是用双端队列，队列的一边永远都存的是窗口的最大值，队列的另外一个边存的是比最大值小的值。队列中最大值左边的所有值都出队。在保证了双端队列的一边即是最大值以后，时间复杂度是 O(n)，空间复杂度是 O(K)
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