计算1！- 2！+3！-……+n!

Question

计算1！- 2！+3！-……+n!麻烦用Python解答一下叭！感谢！

Answer 1

# -*- coding: utf-8 -*-

def fac(n):
    if n == 1:
        return 1
    return n * fac(n - 1)


def fun(n):
    sum = 0
    for i in range(1, n + 1):
        if i % 2 == 0:
            sum -= fac(i)
        else:
            sum += fac(i)
    return sum


if __name__ == '__main__':
    print(fun(3))