682. Maximum Product of Three Numbers

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

Example 1:

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

Example 2:

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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.

解法1：

这题用3Sum smaller的思路，不过是简化了的版本。每对应一个数字，只需要考虑如果是负数时最小的乘积和如果是正数时最大的乘积。
C++

1

Java

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public class Solution {
    public int maximumProduct(int[] nums) {
        if (nums.length == 0 ) {
            return 0;
        }
        Arrays.sort(nums);  // sort ascending
        int res = Integer.MIN_VALUE;
        int n = nums.length;
        for (int i = 0; i < nums.length - 2; i++) {
            if (nums[i] < 0) {
                res = Math.max(res, nums[i] * nums[i + 1] * nums[n - 1]);
            } else if (nums[i] > 0) {
                res = Math.max(res, nums[n - 1] * nums[n - 2] * nums[i]);
            } else {
                res = Math.max(res, 0);
            }
        }
        return res;
    }
}