编辑代码

def cal(num, plate1="a", plate2="b", plate3="c"):
    if num == 1:
        print("{}->{}".format(plate1, plate3))
    else:
        cal(num-1, plate1, plate3, plate2)
        print("{}->{}".format(plate1, plate3))
        cal(num - 1, plate2, plate1, plate3)


if __name__ == '__main__':
    cal(3)