5.最大交替子序列和

class Solution {
public:
    long long maxAlternatingSum(vector<int>& nums) {
        long long even = nums[0], odd = 0;
        for (int i = 1; i < nums.size(); i++) {
            even = max(even, odd + nums[i]);
            odd = max(odd, even - nums[i]);
        }
        return even;
    }
};

https://leetcode.cn/problems/maximum-alternating-subsequence-sum/