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: 6The entire sequence is a wiggle sequence.Input: [1,17,5,10,13,15,10,5,16,8]Output: 7There 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;                    }    };