LeetCode[递归]53. Maximum Subarray 数组最大和

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

.
代码
class Solution
{
public:
int max(int a,int b)
{
return a > b?a:b;
}
int maxSubArray(vector<int>& nums)
{
if(nums.empty()) return 0;
return maxsub(nums,0,(int)nums.size() - 1);
}
int maxsub(vector<int>&nums,int left,int right)
{
if(left >= right) return nums[left];
int mid = left +(right - left)/2;//这里很重要
int lmax = maxsub(nums,left,mid-1);
int rmax = maxsub(nums,mid+1,right);
int mmax = nums[mid],t = mmax;
int i;
for(i = mid - 1;i >= left;i--)
{
t += nums[i];
mmax = max(mmax,t);
}
t = mmax;
for(i = mid+1;i <=right;i++)
{
t += nums[i];
mmax = max(mmax,t);
}
return max(mmax,max(lmax,rmax));
}
};