Description
https://leetcode.com/problems/product-of-array-except-self/
Given an array nums
of n integers where n > 1, return an array output
such that output[i]
is equal to the product of all the elements of nums
except nums[i]
.
Example:
Input:[1,2,3,4]
Output:[24,12,8,6]
Constraint: It’s guaranteed that the product of the elements of any prefix or suffix of the array (including the whole array) fits in a 32 bit integer.
Note: Please solve it without division and in O(n).
Follow up:
Could you solve it with constant space complexity? (The output array does not count as extra space for the purpose of space complexity analysis.)
Explanation
one pass to get products before the target number, one pass to get products after the target number
Python Solution
class Solution:
def productExceptSelf(self, nums: List[int]) -> List[int]:
post_products = []
j = 0
for i in range(len(nums) - 1, -1, -1):
if i == len(nums) - 1:
post_products.append(nums[i])
else:
post_products.append(post_products[j - 1] * nums[i])
j += 1
post_products = post_products[::-1]
pre_products = []
for i in range(0, len(nums)):
if i == 0:
pre_products.append(nums[i])
else:
pre_products.append(pre_products[i - 1] * nums[i])
result = []
for i in range(0, len(nums)):
if i == 0:
result.append(1 * post_products[i + 1])
elif i == len(nums) - 1:
result.append(pre_products[i - 1] * 1)
else:
result.append(pre_products[i - 1] * post_products[i + 1])
return result
- Time complexity: O(N).
- Space complexity: O(N).
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