為什么在某些情況下此腳本陷入無限循環？

Question

我正在重新制作舊的python腳本。 通過一些隨機測試用例運行它時，我注意到在某些情況下它會陷入無限循環，而在其他情況下則不會。 該腳本適用於項目Euler問題3（可用於提示問題，因此從未注意到隨機無限循環）。 這將適用於10、19、51、600851475143。它陷入152的無限循環中。

這是代碼：

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

將n/=d放置在def largestPrime(n): if （但在while內def largestPrime(n):因為在您的代碼中，僅當d大於largest_prime時才執行n/=d ，這是錯誤的。 必須完成n/=d直到n % d == 0

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