"""练习 17 进阶版：用 itertools.permutations 枚举不重复数位。"""
from itertools import permutations

digits = "0123456789"
valid_numbers = (
    number for number in permutations(digits, 3)
    if number[0] != "0" and number[2] in "02468"
)
enumeration_count = sum(1 for _ in valid_numbers)
counting_principle_count = 9 * 8 + 4 * 8 * 8
print("enumeration:", enumeration_count)
print("counting principle:", counting_principle_count)