Product of Array Except Self

Given an integer array nums, return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i].

The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer.

You must write an algorithm that runs in O(n) time and without using the division operation.

Example 1:

Input: nums = [1,2,3,4]
Output: [24,12,8,6]

Example 2:

Input: nums = [-1,1,0,-3,3]
Output: [0,0,9,0,0]

Constraints:

• 2 <= nums.length <= 105
• -30 <= nums[i] <= 30
• The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer.

Follow up: Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)

Solution

class Solution {
    public int[] productExceptSelf(int[] nums) {
        int len = nums.length;
        int result[] = new int [len];
        Arrays.fill(result,1);
        int pre = 1;
        int post = 1;
        for(int i = 0; i < len-1; i++) {
            pre *= nums[i];
            result[i + 1] *= pre;
        }

        for(int j = len-1; j >= 1; j--) {
            post *= nums[j];
            result[j - 1] *= post; 
        }
        
        return result;
    }
}