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.


Note: Notice how the left and right are computed after
     updating the current ans[i] element, so that ans[i]
     is not contributing to the products.
      Also note, how left and right needs to start at 1


def productExceptSelf(nums: List[int]):
   
    ans = []
    left = 1        
    for n in nums:
        ans.append(left)
        left *= n
   
    L = len(nums)
    right = 1        
    for i in reversed(range(L)):
        ans[i] *= right
        right *= nums[i]
   
    return ans

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