Python/project_euler/problem_003/sol1.py
Paulo S. G. Ferraz 1400cb86ff
Remove duplicate is_prime related functions (#5892)
* Fixes (#5434)

* Update ciphers.rabin_miller.py
         maths.miller_rabin.py

* Fixing ERROR maths/miller_rabin.py - ModuleNotFoundError and changing project_euler's isPrime to is_prime function names

* Update sol1.py

* fix: try to change to list

* fix pre-commit

* fix capital letters

* Update miller_rabin.py

* Update rabin_miller.py

Co-authored-by: John Law <johnlaw.po@gmail.com>
2022-04-09 01:40:45 +08:00

105 lines
2.5 KiB
Python

"""
Project Euler Problem 3: https://projecteuler.net/problem=3
Largest prime factor
The prime factors of 13195 are 5, 7, 13 and 29.
What is the largest prime factor of the number 600851475143?
References:
- https://en.wikipedia.org/wiki/Prime_number#Unique_factorization
"""
import math
def is_prime(num: int) -> bool:
"""
Returns boolean representing primality of given number num.
>>> is_prime(2)
True
>>> is_prime(3)
True
>>> is_prime(27)
False
>>> is_prime(2999)
True
>>> is_prime(0)
Traceback (most recent call last):
...
ValueError: Parameter num must be greater than or equal to two.
>>> is_prime(1)
Traceback (most recent call last):
...
ValueError: Parameter num must be greater than or equal to two.
"""
if num <= 1:
raise ValueError("Parameter num must be greater than or equal to two.")
if num == 2:
return True
elif num % 2 == 0:
return False
for i in range(3, int(math.sqrt(num)) + 1, 2):
if num % i == 0:
return False
return True
def solution(n: int = 600851475143) -> int:
"""
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 than or equal to one.
>>> solution(-17)
Traceback (most recent call last):
...
ValueError: Parameter n must be greater than or equal to one.
>>> solution([])
Traceback (most recent call last):
...
TypeError: Parameter n must be int or castable to int.
>>> solution("asd")
Traceback (most recent call last):
...
TypeError: Parameter n must be int or castable to int.
"""
try:
n = int(n)
except (TypeError, ValueError):
raise TypeError("Parameter n must be int or castable to int.")
if n <= 0:
raise ValueError("Parameter n must be greater than or equal to one.")
max_number = 0
if is_prime(n):
return n
while n % 2 == 0:
n //= 2
if is_prime(n):
return n
for i in range(3, int(math.sqrt(n)) + 1, 2):
if n % i == 0:
if is_prime(n // i):
max_number = n // i
break
elif is_prime(i):
max_number = i
return max_number
if __name__ == "__main__":
print(f"{solution() = }")