Daily Coding Problem Solution 2 This problem was asked by Uber.

Given an array of integers, return a new array such that each element at index i of the new array is the product of all the numbers in the original array except the one at i.

For example, if our input was [1, 2, 3, 4, 5], the expected output would be [120, 60, 40, 30, 24]. If our input was [3, 2, 1], the expected output would be [2, 3, 6].

Follow-up: what if you can’t use division?

### A Pythonic Attempt

``````import copy
import functools

mylist1 = [1, 2, 3, 4, 5]
output1 = [120, 60, 40, 30, 24]

mylist2 = [3, 2, 1]
output2 = [2, 3, 6]

def prod_arr(mylist):
# pythonic
ans = []
for i, num in enumerate(mylist):
copied = copy.deepcopy(mylist)
copied.remove(num)
ans.append(functools.reduce(lambda a,b : a*b, copied))
return ans

def prod_arr2(mylist):
# barebones
ans = []
for i, num in enumerate(mylist):
prod = 1
for i2, num2 in enumerate(mylist):
if i2 != i:
prod *= num2
ans.append(prod)
return ans

assert prod_arr(mylist1) == output1, 'fail'
assert prod_arr(mylist2) == output2, 'fail'

assert prod_arr2(mylist1) == output1, 'fail'
assert prod_arr2(mylist2) == output2, 'fail'

``````

### The Real Solution Online

``````def products(nums):
# Generate prefix products
prefix_products = []
for num in nums:
if prefix_products:
prefix_products.append(prefix_products[-1] * num)
else:
prefix_products.append(num)

# Generate suffix products
suffix_products = []
for num in reversed(nums):
if suffix_products:
suffix_products.append(suffix_products[-1] * num)
else:
suffix_products.append(num)
suffix_products = list(reversed(suffix_products))

# Generate result
result = []
for i in range(len(nums)):
if i == 0:
result.append(suffix_products[i + 1])
elif i == len(nums) - 1:
result.append(prefix_products[i - 1])
else:
result.append(prefix_products[i - 1] * suffix_products[i + 1])
return result

``````