1464.md

1464. Maximum Product of Two Elements in an Array

Level:

Topic:

Question

Given the array of integers nums, you will choose two different indices i and j of that array. Return the maximum value of (nums[i]-1)*(nums[j]-1).

Input: nums = [3,4,5,2]
Output: 12
Explanation: If you choose the indices i=1 and j=2 (indexed from 0), you will get the maximum value, that is, (nums[1]-1)(nums[2]-1) = (4-1)(5-1) = 3*4 = 12.

Intuition

Keep two counter variables (max1, max2)

• if there is a num >= max2, replace max1 with max2 and update max2
• if there is a num > max1, update max1

[3, 4, 5, 2]
element   max1 max2
   3       3    0
   4       4    3
   5       5    4
   2       5    4

Code

Time: O(n)
Space: O(1)

public int maxProduct(int[] nums) {
    int max1 = 0, max2 = 0;
    for (int num: nums) {
        if (num > max1) {
            max2 = max1;
            max1 = num;
        } else if (num > max2) {
            max2 = num;
        }
    }
    return (max1-1) * (max2-1);
}