Wiggle Subsequence

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?

class Solution {
public:
int wiggleMaxLength(vector<int>& nums) {
int n=nums.size();
if(n<=2) return n;
int nextWanted=0;
int maxLen=1;
for(int i=1;i<n;i++){
if(nums[i]>nums[i-1]&&(nextWanted==0||nextWanted==-1)){
nextWanted=1;
maxLen++;
}else if(nums[i]<nums[i-1]&&(nextWanted==0||nextWanted==1)){
nextWanted=-1;
maxLen++;
}
}
return maxLen;

}

};