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238. Product Of Array Except Self

Array Prefix Sum

Problem - Product Of Array Except Self

Medium

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.)

Solutions

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class Solution:
    def productExceptSelf(self, nums: List[int]) -> List[int]:
        n = len(nums)
        answer = [0] * n
        left = right = 1

        for i, val in enumerate(nums):
            answer[i] = left
            left *= val

        for i in range(n - 1, -1, -1):
            answer[i] *= right
            right *= nums[i]

        return answer

Submission Stats:

  • Runtime: 19 ms (86.71%)
  • Memory: 23.1 MB (94.07%)