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.

 解法 :
          將這一串的array先做排序，這樣就可以讓最後面的三個數字的積或是最前面的兩個數跟最後一個數的積變成最大值(ex. [-9,-8,1,9])

class Solution {
public:
    int maximumProduct(vector<int>& nums) {
        
        if (nums.size() < 3)
        {
            return 0;
        }
        
        sort(nums.begin(), nums.end());
        
        int firsthree =  nums[0] * nums[1] * nums[nums.size() -1]
            ,lastthree = nums[nums.size() -1] * nums[nums.size() -2] * nums[nums.size() -3];
            
        return firsthree >  lastthree ?  firsthree : lastthree;
    }
};