使用枚举法验证6174猜想

from string import digits
from itertools import combinations


for item in combinations(digits, 4):
    times = 0
    while True:
        big = int(''.join(sorted(item, reverse=True)))
        little = int(''.join(sorted(item)))
        difference = big-little
        times = times+1
        if difference == 6174:
            if times > 7:
                print(times)
            break
        else:
            item = str(difference)

如果什么都没打印,则证明猜想