238. Product of Array Except Self

Product of Array Except Self

Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].

Solve it without division and in O(n).

For example, given [1,2,3,4], return [24,12,8,6].

Follow up: Could you solve it with constant space complexity? (Note: The output array does not count as extra space for the purpose of space complexity analysis.)

Solution

public class Solution {
     public int[] productExceptSelf(int[] nums) {
        if (nums == null) return null;

        int size = nums.length;
        int[] result = new int[size];

        for (int i = 1; i <= size - 1; i++) {
            if (i == 1) {
                result[i] = nums[i - 1];
            } else {
                result[i] = result[i - 1] * nums[i - 1];
            }
        }

        int left = nums[size - 1];
        for (int i = size - 2; i >= 0; i--) {
            if (i==0) result[i] = left;
            else {
            result[i] *= left;}
            left *= nums[i];
        }
        return result;
    }
}