Created
January 14, 2009 00:03
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A Python solution to Project Euler Problem 3
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def factors(num): | |
"""Generates the factors for num. | |
By PEZ, from a description by BradC over at Stackoverflow.com | |
http://stackoverflow.com/questions/439814#439850 | |
""" | |
from math import sqrt | |
def _candidates(): | |
"""Generates the sequence 2, then all odd ints starting with 3""" | |
c = 2 | |
yield c | |
c += 1 | |
while True: | |
yield c | |
c += 2 | |
start = num | |
candidates = _candidates() | |
candidate = candidates.next() | |
sqrt_num = sqrt(num) | |
while candidate < sqrt_num: | |
while num % candidate == 0: | |
yield candidate | |
num /= candidate | |
sqrt_num = sqrt(num) | |
if candidate > sqrt_num: | |
yield num | |
return | |
candidate = candidates.next() | |
if num < start: | |
yield num | |
if __name__=='__main__': | |
# The number 600851475143 takes 0.002 secs to factor on my MacBook | |
from timeit import Timer | |
t = Timer("print list(factors(600851475143))", "from __main__ import factors") | |
print "%.5f" % t.timeit(1) | |
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