A sequence of numbers is called a wiggle sequence if 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.
Given a sequence of integers, return the length of the longest subsequence that is a wiggle sequence. A subsequence is obtained by deleting some number of elements (eventually, also zero) from the original sequence, leaving the remaining elements in their original order.
Examples:
Input: [1,7,4,9,2,5]
Output: 6
The entire sequence is a wiggle sequence.
Input: [1,17,5,10,13,15,10,5,16,8]
Output: 7
There are several subsequences that achieve this length. One is [1,17,10,13,10,16,8].
Input: [1,2,3,4,5,6,7,8,9]
Output: 2
Follow up:
Can you do it in O(n) time?
Credits:Special thanks to @agave and @StefanPochmann for adding this problem and creating all test cases.
class Solution:
     def wiggleMaxLength(self, nums):
         """
         :type nums: List[int]
         :rtype: int
         """
         nums = [nums[i] for i in range(len(nums)) if i == 0 or nums[i] != nums[i-1]]
         print(nums)
         total = min(2,len(nums))
         for i in range(1,len(nums)-1):
             if nums[i] > nums[i-1] and nums[i] > nums[i+1]:
                 total += 1
             elif nums[i] < nums[i-1] and nums[i] < nums[i+1]:
                 total += 1
         return total
class Solution:
     def wiggleMaxLength(self, nums):
         """
         :type nums: List[int]
         :rtype: int
         """
         nums = [nums[i] for i in range(len(nums)) if i == 0 or nums[i] != nums[i-1]]
         print(nums)
         total = min(2,len(nums))
         for i in range(1,len(nums)-1):
             if nums[i] > nums[i-1] and nums[i] > nums[i+1]:
                 total += 1
             elif nums[i] < nums[i-1] and nums[i] < nums[i+1]:
                 total += 1
         return total