使用归并排序和快速排序：时间复杂度为O(nlogn)，快排132ms，归并880ms，stl 的sort() 80ms

考虑到负数，最大值有两种情况：两个负数一个正数相乘，或者三个正数相乘，取两个的最大值

class Solution {public:    int findpivot(vector
     
      &nums,int start,int end){        int pivot=nums[start];        int i=start,j=end;        while(i
      
       =pivot)                j--;            nums[i]=nums[j];            while(i
       
        <=pivot)                i++;            nums[j]=nums[i];        }        nums[i]=pivot;        return i;    }    void quicksort(vector
        
         &nums,int start,int end){        if(start>=end) return;        int pivotkey=findpivot(nums,start,end);        quicksort(nums,start,pivotkey-1);        quicksort(nums,pivotkey+1,end);    }            void merge(vector
         
          &nums,int start,int mid,int end){        vector
          
            tmp; int i=start,j=mid+1; while(i<=mid&&j<=end){ if(nums[i]
           

&nums,int start,int end){ if(start==end) return; int mid=(end-start)/2+start; mergesort(nums,start,mid); mergesort(nums,mid+1,end); merge(nums,start,mid,end); } int maximumProduct(vector

& nums) { int len=nums.size(); if(len<3) return 0; //mergesort(nums,0,len-1); quicksort(nums,0,len-1); //sort(nums.begin(),nums.end()); return max(nums[0]*nums[1]*nums[len-1],nums[len-3]*nums[len-2]*nums[len-1]); } };