求一个数组中的连续的和最大的子数组。采用滑动窗口解决。sum 如果小于0，置为0，再加上当前值。然后再与max相比，取大的-Seeking a continuous array and the largest sub-array. Sliding window resolved. If the sum is less than 0, set to 0, plus the current value. Then compared to the max, whichever is greater