LeetCode/238_Product_of_Array_Except_Self.py at main · AnmolPatel20/LeetCode · GitHub

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"""
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.)
"""

class Solution:
    def productExceptSelf(self, nums: List[int]) -> List[int]:
        result = [1] * (len(nums)) #Giving each pos the initial value
        prefix = 1
        for i in range(len(nums)):
            result[i] = prefix
            prefix *= nums[i]

        postfix = 1
        for i in range(len(nums)-1,-1,-1):
            result[i] *= postfix #mul with the already prefix in res
            postfix *= nums[i]

        return result