[leetcode]152. Maximum Subarray

题目链接：https://leetcode.com/problems/maximum-subarray/description/

Find the contiguous subarray within an array (containing at least one number) which has the largest sum.

For example, given the array [-2,1,-3,4,-1,2,1,-5,4],
the contiguous subarray [4,-1,2,1] has the largest sum = 6.

思路：动态规划。每一步维护局部最优解maxm和全局最优解res，因为在每一步中，如果遇到负数，相加之前肯定比原值小，比当前值可能大、可能小。所以，对于每一步相加，要处理局部和全局的关系，

状态转移方程：maxm=max(maxm+nums[i] ,nums[i])

                         res=max(res,maxm)

class Solution{public:    int maxSubArray(vector<int>& nums)    {        int len=nums.size();        if (len==1)            return nums[0];        int maxm=nums[0],res=nums[0];        for(int i=1;i<len;i++)        {            maxm=max(maxm+nums[i],nums[i]);            res=max(res,maxm);        }        return res;    }};