376. 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.

class Solution {public:    int wiggleMaxLength(vector<int>& nums) {        int n = nums.size();    if(n == 0) return 0;        int s1[n],s2[n];        s1[0] = 1;        s2[0] = 1;        for(int i = 1; i < n; i ++)        {        if(nums[i] > nums[i-1])        {        s1[i] = s2[i - 1] + 1;        s2[i] = s2[i - 1];        }        else if(nums[i] < nums[i-1])        {        s2[i] = s1[i - 1] + 1;        s1[i] = s1[i - 1];                }        else        {        s1[i] = s1[i-1];        s2[i] = s2[i-1];        }        }        return max(s1[n-1],s2[n-1]);    }};