【LeetCode 628】 Maximum Product of Three Numbers

题目描述

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:

The length of the given array will be in range [3,104] and all elements are in the range [-1000, 1000].
Multiplication of any three numbers in the input won’t exceed the range of 32-bit signed integer.

思路

根据数据范围，考虑负数的情况。

代码

class Solution {
public:
    int maximumProduct(vector<int>& nums) {
        int n = nums.size();
        vector<int> neg;
        vector<int> pos;
        
        for (int i=0; i<nums.size(); ++i) {
            if (i < 0 || nums.empty()) break;
            if (nums[i] < 0) {
                neg.push_back(nums[i]);
            }else {
                pos.push_back(nums[i]);
            }
        }
        sort(pos.begin(), pos.end());
        sort(neg.begin(), neg.end());
        
        int n1 = pos.size();
        int n2 = neg.size();
        
        int res = INT_MIN;
        if (n1 >= 3)
            res = max(res, pos[n1-1] * pos[n1-2] * pos[n1-3]);
        if (n2 == n) 
            res = max(res, neg[n2-1] * neg[n2-2] * neg[n2-3]);
        if (n2 >= 2 && n1 >= 1) 
            res = max(res, neg[0] * neg[1] * pos[n1-1]);
        return res;
    }
};