1019 数字黑洞 (20分)

输入样例 1：

6767
输出样例 1：

7766 - 6677 = 1089
9810 - 0189 = 9621
9621 - 1269 = 8352
8532 - 2358 = 6174
输入样例 2：

2222

解体心得：

1. 在初次写str2list时没有考虑到输入是‘123’这样的情形；

# -*- coding: utf-8 -*-
import sys


def str2list(in_str):
    result = [c for c in in_str]
    result = ['0'] * (4 - len(result)) + result
    return result


def kaprekar_process(in_str):
    asc_num = sorted(str2list(in_str))
    des_num = sorted(asc_num, reverse=True)
    difference = int(''.join(des_num)) - int(''.join(asc_num))
    while difference != 0 and difference != 6174:
        print('%04d - %04d = %04d' % (int(''.join(des_num)), int(''.join(asc_num)), difference))
        asc_num = sorted(str2list(str(difference)))
        des_num = sorted(asc_num, reverse=True)
        difference = int(''.join(des_num)) - int(''.join(asc_num))
    print('%04d - %04d = %04d' % (int(''.join(des_num)), int(''.join(asc_num)), difference))


if __name__ == '__main__':
    input_str = sys.stdin.readline().strip()
    kaprekar_process(input_str)