238. Product of Array Except Self

1. Question:

238. Product of Array Except Self

https://leetcode.com/problems/product-of-array-except-self/

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

Example:

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

Note: Please solve it without division and in O(n).

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

2. Solution:

class Solution:
    def productExceptSelf(self, nums):
        """
        :type nums: List[int]
        :rtype: List[int]
        """
        re = []
        if nums is None:
            return re

        size = len(nums)
        re = [1 for v in range(size)]

        for i in range(1, size):
            re[i] = re[i - 1] * nums[i - 1]

        right_product = 1
        for i in range(-1, -size - 1, -1):
            re[i] = re[i] * right_product
            right_product *= nums[i]

        return re

3. Complexity Analysis

Time Complexity : O(N)

Space Complexity: O(1)