LeetCode#628: Maximum Product of Three Numbers

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Description

Given an integer array, find three numbers whose product is maximum and output the maximum product.

Example

Input: [1,2,3]
Output: 6

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.

Solution

这道题需要注意最大值不一定是最大的三个数相乘，当最小的两个数为负数时，有可能是最小的两个数与最大的一个数相乘，比如：{-2, -5, 1, 2, 3}，最大值应该为-2 * -5 * 3 = 30 而不是 1 * 2 * 3 = 6。

public class Solution {
    public int maximumProduct(int[] nums) {
    	int max1 = Integer.MIN_VALUE;
    	int max2 = Integer.MIN_VALUE;
    	int max3 = Integer.MIN_VALUE;
    	
    	int min1 = Integer.MAX_VALUE;
    	int min2 = Integer.MAX_VALUE;
    	
    	for(int i = 0; i < nums.length; i++) {
    		if(nums[i] > max1) {
    			max3 = max2;
    			max2 = max1;
    			max1 = nums[i];
    		} else if(nums[i] > max2) {
    			max3 = max2;
    			max2 = nums[i];
    		} else if(nums[i] > max3) {
    			max3 = nums[i];
    		}
    		if(nums[i] < min1) {
    			min2 = min1;
    			min1 = nums[i];
    		} else if(nums[i] < min2){
    			min2 = nums[i];
    		}
    	}
    	return Math.max(max1 * max2 * max3, min1 * min2 * max1);
    }
}