Given an integer array nums, return the length of the longest wiggle sequence.
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 fewer than two elements is trivially a wiggle sequence.
- For example,
[1, 7, 4, 9, 2, 5]is a wiggle sequence because the differences(6, -3, 5, -7, 3)are alternately positive and negative. - In contrast,
[1, 4, 7, 2, 5]and[1, 7, 4, 5, 5]are not wiggle sequences, the first because its first two differences are positive and the second because its last difference is zero.
A subsequence is obtained by deleting some elements (eventually, also zero) from the original sequence, leaving the remaining elements in their original order.
Example 1:
Input: nums = [1,7,4,9,2,5] Output: 6 Explanation: The entire sequence is a wiggle sequence.
Example 2:
Input: nums = [1,17,5,10,13,15,10,5,16,8] Output: 7 Explanation: There are several subsequences that achieve this length. One is [1,17,10,13,10,16,8].
Example 3:
Input: nums = [1,2,3,4,5,6,7,8,9] Output: 2
Constraints:
1 <= nums.length <= 10000 <= nums[i] <= 1000
Follow up: Could you solve this in O(n) time?