0238: Product of Array Except Self

Problem Statement

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 input is generated such that answer[i] 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.)

Code Solution

class Solution:
    def productExceptSelf(self, nums):
        N = len(nums)
        res = [1] * N
        prod = 1
        for ix in range(0, N, 1):
            res[ix] *= prod
            prod *= nums[ix]
        prod = 1
        for ix in range(N - 1, -1, -1):
            res[ix] *= prod
            prod *= nums[ix]
        return res