Given an integer array, find three numbers whose product is maximum and output the maximum product.

Example 1:

Input: [1,2,3]
Output: 6

Example 2:

Input: [1,2,3,4]
Output: 24

Note:

1. The length of the given array will be in range [3,104] and all elements are in the range [-1000, 1000].
2. Multiplication of any three numbers in the input won‘t exceed the range of 32-bit signed integer.

找出3个数，使他们的乘积最大，数字会有负数

C++（79ms）：

 1 class Solution {
 2 public:
 3     int maximumProduct(vector<int>& nums) {
 4         sort(nums.begin(),nums.end()) ;
 5         int a = nums[0] * nums[1] * nums[nums.size()-1] ;
 6         int b = nums[nums.size()-3] * nums[nums.size()-2] * nums[nums.size()-1] ;
 7         if (a >= b)
 8             return a ;
 9         else
10             return b ;
11     }
12 };