50 lines
1.1 KiB
Python
Executable File
50 lines
1.1 KiB
Python
Executable File
#! /usr/bin/env python3
|
|
|
|
# Factorize numbers.
|
|
# The algorithm is not efficient, but easy to understand.
|
|
# If there are large factors, it will take forever to find them,
|
|
# because we try all odd numbers between 3 and sqrt(n)...
|
|
|
|
import sys
|
|
from math import sqrt
|
|
|
|
def fact(n):
|
|
if n < 1:
|
|
raise ValueError('fact() argument should be >= 1')
|
|
if n == 1:
|
|
return [] # special case
|
|
res = []
|
|
# Treat even factors special, so we can use i += 2 later
|
|
while n % 2 == 0:
|
|
res.append(2)
|
|
n //= 2
|
|
# Try odd numbers up to sqrt(n)
|
|
limit = sqrt(n+1)
|
|
i = 3
|
|
while i <= limit:
|
|
if n % i == 0:
|
|
res.append(i)
|
|
n //= i
|
|
limit = sqrt(n+1)
|
|
else:
|
|
i += 2
|
|
if n != 1:
|
|
res.append(n)
|
|
return res
|
|
|
|
def main():
|
|
if len(sys.argv) > 1:
|
|
source = sys.argv[1:]
|
|
else:
|
|
source = iter(input, '')
|
|
for arg in source:
|
|
try:
|
|
n = int(arg)
|
|
except ValueError:
|
|
print(arg, 'is not an integer')
|
|
else:
|
|
print(n, fact(n))
|
|
|
|
if __name__ == "__main__":
|
|
main()
|