为什么这个脚本在某些情况下会陷入无限循环？

Question

我正在重新编写旧的 python 脚本。虽然运行它通过了一些随机测试用例，但我注意到它会在某些情况下陷入无限循环，但对于其他情况则不会。此脚本适用于 Project Euler Problem 3（适用于问题提示，因此从未注意到随机无限循环）。这将适用于 10、19、51、600851475143。它会陷入 152 的无限循环。我没有尝试过其他的，但认为这足以引起注意 'odd'.

的测试用例

代码如下：

import sys

def largestPrime(n):
    largest_prime = 0 # initialize largest prime
    d = 2 # set first value for factor evaluation

    while n > 1: # n will be divided by each factor later on
        while n % d == 0: # check if n is divisible by factor
            if d > largest_prime: # check if d is greater than largest_prime
                largest_prime = d # if so, set largest_prime = d
                n /= d # if so, can divide n by d to find remaining factors
        d += 1

    return largest_prime


def main():
    # Make a list of command line arguments, omitting the [0] element
    # which is the script itself.
    args = sys.argv[1:]
    if not args: #if list is empty; return message & exit
        print ("Usage: euler003.py 'n'")
        sys.exit(1)

    if len(args) > 1: #if list less than 1; return message & exit
        print ("You've entered too many arguments; Usage: euler001.py 'n'")
        sys.exit(1)

    largest = largestPrime(int(args[0]))
    print (largest)


# This is the standard boilerplate that calls the main() function.    
if __name__ == "__main__":
    main()

Answer 1

将 n/=d 放在 if 之外（但在 while 之内）在 def largestPrime(n): 因为在你的代码中，只有当 d 大于 largest_prime 这是错误的。 n/=d 必须完成到 n % d == 0

while n % d == 0: 
    if d > largest_prime:
       largest_prime = d 
    n /= d 
d += 1

为什么这个脚本在某些情况下会陷入无限循环？

Why does this script get stuck in infinite loop for some cases?

python

while-loop

infinite-loop