leetcode-376 Wiggle Subsequence

Example 1:

Input: [1,7,4,9,2,5]
Output: 6
Explanation: The entire sequence is a wiggle sequence.
Example 2:

Input: [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: [1,2,3,4,5,6,7,8,9]
Output: 2

class Solution {
public:
    int wiggleMaxLength(vector<int>& nums) {
        if(nums.size() < 2)
            return nums.size();
        
        int prevdiff = nums[1]-nums[0];
        int count = prevdiff != 0 ? 2 : 1;
        for(int i=2; i<nums.size(); i++){
            int diff = nums[i]-nums[i-1];
            if((diff > 0 && prevdiff <= 0) || (diff < 0 && prevdiff >= 0)){
                count++;
                prevdiff = diff;
            }
        }
        return count;
    }
};