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

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

神马复杂度为n^2,n^3的解法肯定是会超时的,ok目标为O(n);

LeetCode : Maximum Product Subarray