A wiggle sequence is a sequence where the differences between successive numbers strictly alternate between positive and negative. The first difference (if one exists) may be either positive or negative. A sequence with one element and a sequence with two non-equal elements are trivially wiggle sequences.
\n\n[1, 7, 4, 9, 2, 5] is a wiggle sequence because the differences (6, -3, 5, -7, 3) alternate between positive and negative.[1, 4, 7, 2, 5] and [1, 7, 4, 5, 5] are not wiggle sequences. The first is not because its first two differences are positive, and the second is not because its last difference is zero.A subsequence is obtained by deleting some elements (possibly zero) from the original sequence, leaving the remaining elements in their original order.
\n\nGiven an integer array nums, return the length of the longest wiggle subsequence of nums.
\n
Example 1:
\n\n\nInput: nums = [1,7,4,9,2,5]\nOutput: 6\nExplanation: The entire sequence is a wiggle sequence with differences (6, -3, 5, -7, 3).\n\n\n
Example 2:
\n\n\nInput: nums = [1,17,5,10,13,15,10,5,16,8]\nOutput: 7\nExplanation: There are several subsequences that achieve this length.\nOne is [1, 17, 10, 13, 10, 16, 8] with differences (16, -7, 3, -3, 6, -8).\n\n\n
Example 3:
\n\n\nInput: nums = [1,2,3,4,5,6,7,8,9]\nOutput: 2\n\n\n
\n
Constraints:
\n\n1 <= nums.length <= 10000 <= nums[i] <= 1000\n
Follow up: Could you solve this in O(n) time?
如果连续数字之间的差严格地在正数和负数之间交替，则数字序列称为 摆动序列 。第一个差（如果存在的话）可能是正数或负数。仅有一个元素或者含两个不等元素的序列也视作摆动序列。
\n\n例如， [1, 7, 4, 9, 2, 5] 是一个 摆动序列 ，因为差值 (6, -3, 5, -7, 3) 是正负交替出现的。
[1, 4, 7, 2, 5] 和 [1, 7, 4, 5, 5] 不是摆动序列，第一个序列是因为它的前两个差值都是正数，第二个序列是因为它的最后一个差值为零。子序列 可以通过从原始序列中删除一些（也可以不删除）元素来获得，剩下的元素保持其原始顺序。
\n\n给你一个整数数组 nums ，返回 nums 中作为 摆动序列 的 最长子序列的长度 。
\n\n
示例 1：
\n\n\n输入：nums = [1,7,4,9,2,5]\n输出：6\n解释：整个序列均为摆动序列，各元素之间的差值为 (6, -3, 5, -7, 3) 。\n\n\n
示例 2：
\n\n\n输入：nums = [1,17,5,10,13,15,10,5,16,8]\n输出：7\n解释：这个序列包含几个长度为 7 摆动序列。\n其中一个是 [1, 17, 10, 13, 10, 16, 8] ，各元素之间的差值为 (16, -7, 3, -3, 6, -8) 。\n\n\n
示例 3：
\n\n\n输入：nums = [1,2,3,4,5,6,7,8,9]\n输出：2\n\n\n
\n\n
提示：
\n\n1 <= nums.length <= 10000 <= nums[i] <= 1000\n\n
进阶：你能否用 O(n) 时间复杂度完成此题?
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