238. Product of Array Except Self.py

"""
238. 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."""

class Solution:
    def productExceptSelf(self, nums: List[int]) -> List[int]:
        answer = []
        previous = 1
        left = [1]
        right = [1]
        for value in range(len(nums)-1):
            product = previous * nums[value]
            previous = product
            left.append(previous)
        previous = 1
        nums = nums[::-1]
        for value in range(len(nums)-1):
            product = previous * nums[value]
            previous = product
            right.append(product)
        right= right[::-1]
        for x,y in zip(left, right):
            answer.append(x*y)
        return answer