Leetcode

Leetcode - 628 Maximum Product of Three Numbers

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.

题解：

 　　O(n) 的时间复杂度， 将整个数组扫一遍， 找到最大的三个数， 和最小的两个数（有可能是负数）， 在他们的组合中中找最大。

class Solution {
public:
    int maximumProduct(vector<int>& nums) {
        int ans, fs_m=1000 , sd_m=1000, th_m=1000, fs=-1000, sd=-1000, th=-1000; 
        for(int i=0; i<nums.size(); ++i){
            if(nums[i] >= fs){
                th = sd; 
                sd = fs; 
                fs = nums[i]; 
            }else if(nums[i] >= sd){
                th = sd; 
                sd = nums[i]; 
            }else if(nums[i] > th){
                th = nums[i]; 
            }
            
            if(nums[i] < fs_m){
                th_m = sd_m; 
                sd_m = fs_m; 
                fs_m = nums[i]; 
            }else if(nums[i] <= sd_m){
                th_m = sd_m; 
                sd_m = nums[i]; 
            }else if(nums[i] < th_m){
                th_m = nums[i]; 
            }
        }
        
        ans = max(-1000000000, th*sd*fs); 
        ans = max(ans, fs*sd_m*fs_m); 
        
        return ans; 
    }
};