Wiggle Subsequence

A wiggle sequence is one where the differences between successive numbers strictly alternate between positive and negative. Given an integer array nums, return the length of the longest wiggle subsequence (you can delete elements, not necessarily contiguous). A single-element array is trivially a wiggle sequence.

Examples
Input: [1,7,4,9,2,5]
Output: 6
Hints

Wiggle Subsequence

A wiggle sequence is one where the differences between successive numbers strictly alternate between positive and negative. Given an integer array nums, return the length of the longest wiggle subsequence (you can delete elements, not necessarily contiguous). A single-element array is trivially a wiggle sequence.