Array & Hashing
04. 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.
Examples
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 <= 10^5
- -30 <= nums[i] <= 30
- The input is generated such that answer[i] fits 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.)
from typing import List
class Solution:
def productExceptSelf(self, nums: List[int]) -> List[int]:
n: int = len(nums)
answer: List[int] = [1] * n # final result
# Step 1: compute prefix products (left to right)
prefix: int = 1
for i in range(n):
answer[i] = prefix
prefix *= nums[i]
# Step 2: compute suffix products (right to left)
suffix: int = 1
for i in range(n - 1, -1, -1):
answer[i] *= suffix
suffix *= nums[i]
return answerKeyboard shortcuts
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