628. Maximum Product of Three Numbers

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.

解题思路：

　　排序后两种情况，3个都是正数最大，2个是负数最小，一个是正数最大比大小。

　　

class Solution {
public:
    int maximumProduct(vector<int>& nums) {

        if(nums.size()<3) return 0;
        if(nums.size()==3) return nums[0]*nums[1]*nums[2];
        int max_product=1;
        int max_neg=1;
        int n =nums.size();
        sort(nums.begin(),nums.end());

        if(nums[n-3]>=0)
        max_product = nums[n-3]*nums[n-2]*nums[n-1];

        if(nums[1]<=0)
            max_neg=nums[0]*nums[1]*nums[n-1];

        return max_product>=max_neg?max_product:max_neg;


    }
};