Maximum Subarray**

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.

public int maxSubArray(int[] nums) {
        int length = nums.length;
        long max = nums[0];
        long tmpsum = 0;
        for (int i = 0; i < length; i++) {
            tmpsum+=nums[i];
            max = Math.max(max,tmpsum);
            if (tmpsum<0){
                tmpsum=0;
            }
        }
        return (int)max;
    }

很巧妙的：如果array[i...j]为最大和子串，则i<=k<=j，array[i...k]>0