题目原型：
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.
click to show more practice.
More practice:If you have figured out the O(n) solution, try coding another solution using the divide and conquer approach, which is more subtle.
基本思路：
令数组为A，从前往后累加得tmp，sum为最大的累加和。
1、如果A[i]>A[i]+tmp,表示，加了还不如不加，那么初始化tmp，令tmp=A[i]。若tmp>sum，则更新sum 。
2、否则，累加tmp，同时注意更新sum。
public int maxSubArray(int[] A)
{
if(A.length==0||A==null)
return 0;
int sum = A[0];
int tmp = A[0];
for(int i = 1;i
tmp+A[i])
{
tmp = A[i];
}
else
{
tmp+=A[i];
}
if(sum