Python/project_euler/problem_03/sol1.py

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"""
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Problem:
The prime factors of 13195 are 5,7,13 and 29. What is the largest prime factor
of a given number N?
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e.g. for 10, largest prime factor = 5. For 17, largest prime factor = 17.
"""
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from __future__ import print_function, division
import math
try:
raw_input # Python 2
except NameError:
raw_input = input # Python 3
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def isprime(no):
if no == 2:
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return True
elif no % 2 == 0:
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return False
sq = int(math.sqrt(no)) + 1
for i in range(3, sq, 2):
if no % i == 0:
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return False
return True
def solution(n):
"""Returns the largest prime factor of a given number n.
>>> solution(13195)
29
>>> solution(10)
5
>>> solution(17)
17
>>> solution(3.4)
3
>>> solution(0)
Traceback (most recent call last):
...
ValueError: Parameter n must be greater or equal to one.
>>> solution(-17)
Traceback (most recent call last):
...
ValueError: Parameter n must be greater or equal to one.
>>> solution([])
Traceback (most recent call last):
...
TypeError: Parameter n must be int or passive of cast to int.
>>> solution("asd")
Traceback (most recent call last):
...
TypeError: Parameter n must be int or passive of cast to int.
"""
try:
n = int(n)
except (TypeError, ValueError) as e:
raise TypeError("Parameter n must be int or passive of cast to int.")
if n <= 0:
raise ValueError("Parameter n must be greater or equal to one.")
maxNumber = 0
if isprime(n):
return n
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else:
while n % 2 == 0:
n = n / 2
if isprime(n):
return int(n)
else:
n1 = int(math.sqrt(n)) + 1
for i in range(3, n1, 2):
if n % i == 0:
if isprime(n / i):
maxNumber = n / i
break
elif isprime(i):
maxNumber = i
return maxNumber
if __name__ == "__main__":
print(solution(int(raw_input().strip())))