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59 lines
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Markdown
Executable File
59 lines
2.0 KiB
Markdown
Executable File
# [978. Longest Turbulent Subarray](https://leetcode.com/problems/longest-turbulent-subarray/)
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## 题目
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A subarray `A[i], A[i+1], ..., A[j]` of `A` is said to be *turbulent* if and only if:
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- For `i <= k < j`, `A[k] > A[k+1]` when `k` is odd, and `A[k] < A[k+1]` when `k` is even;
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- **OR**, for `i <= k < j`, `A[k] > A[k+1]` when `k` is even, and `A[k] < A[k+1]` when `k` is odd.
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That is, the subarray is turbulent if the comparison sign flips between each adjacent pair of elements in the subarray.
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Return the **length** of a maximum size turbulent subarray of A.
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**Example 1:**
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Input: [9,4,2,10,7,8,8,1,9]
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Output: 5
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Explanation: (A[1] > A[2] < A[3] > A[4] < A[5])
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**Example 2:**
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Input: [4,8,12,16]
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Output: 2
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**Example 3:**
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Input: [100]
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Output: 1
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**Note:**
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1. `1 <= A.length <= 40000`
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2. `0 <= A[i] <= 10^9`
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## 题目大意
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当 A 的子数组 A[i], A[i+1], ..., A[j] 满足下列条件时，我们称其为湍流子数组：
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若 i <= k < j，当 k 为奇数时， A[k] > A[k+1]，且当 k 为偶数时，A[k] < A[k+1]；
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或 若 i <= k < j，当 k 为偶数时，A[k] > A[k+1] ，且当 k 为奇数时， A[k] < A[k+1]。
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也就是说，如果比较符号在子数组中的每个相邻元素对之间翻转，则该子数组是湍流子数组。
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返回 A 的最大湍流子数组的长度。
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提示：
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- 1 <= A.length <= 40000
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- 0 <= A[i] <= 10^9
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## 解题思路
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- 给出一个数组，要求找出“摆动数组”的最大长度。所谓“摆动数组”的意思是，元素一大一小间隔的。
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- 这一题可以用滑动窗口来解答。用一个变量记住下次出现的元素需要大于还是需要小于前一个元素。也可以用模拟的方法，用两个变量分别记录上升和下降数字的长度。一旦元素相等了，上升和下降数字长度都置为 1，其他时候按照上升和下降的关系增加队列长度即可，最后输出动态维护的最长长度。
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