Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum.

Example:

Input: [-2,1,-3,4,-1,2,1,-5,4],
Output: 6
Explanation: [4,-1,2,1] has the largest sum = 6.

 

Greedy, 每个小步骤都pick局部最优。这里的话track一个local sum，如果local sum都小于零了直接把local sum更新为0，因为扫到下一个数的时候，它本身都比它加这串小于0的数要大呀。

leetcode的OJ不需要考虑input为空的情况，实际写的时候要问清楚

 

实现：

class Solution {
public:
    int maxSubArray(vector<int>& nums) {
        
        int maxSum = nums[0];
        int localSum = 0;
        
        for (int num : nums){
            localSum += num;
            maxSum = max(maxSum, localSum);
            localSum = max(0, localSum);
        }
        
        return maxSum;
        
    }
};