def factorial(n):
    if type(n) is int or type(n) is float:
        if n == 1 or n == 0:
            return 1
        elif n < 0:
            return None
        else:
            return factorial(int(n-1)) * int(n)
    else:
        return None


def digits_r2l(n):
    if type(n) is not int or n < 0:
        return None
    elif n < 10:
        return str(n)
    else:
        s = str(n % 10)
    return s + " " + digits_r2l(n // 10)


def digits_l2r(n):
    if type(n) is not int or n < 0:
        return None
    elif n < 10:
        return str(n)
    else:
        s = str(n % 10)
    return digits_l2r(n // 10) + " " + s



#################################################
def verifier(test_name, actual, expected):
    print(test_name)
    if actual != expected:
        print("=======> FAILED! <=======")
        print(f"Got value <{actual}>")
        print(f"Expected value is <{expected}>")
    else:
        print("PASSED")
    print()


fact_tests = [(0, 1),
              (1, 1),
              (7, 5040),
              (-1, None),
              (1.1, 1),
              (5.4, 120),
              ("Str", None),
              (True, None)]

dr2l_tests = [(100, "0 0 1"),
              (9871, "1 7 8 9"),
              (1, "1"),
              (-100, None),
              (1.1, None),
              (5.4, None),
              ("Str", None),
              (True, None)]

dl2r_tests = [(100, "1 0 0"),
              (9871, "9 8 7 1"),
              (1, "1"),
              (-100, None),
              (1.1, None),
              (5.4, None),
              ("Str", None),
              (True, None)]


for i in range(len(fact_tests)):
    verifier(f"Factorial test {i+1}", factorial(fact_tests[i][0]), fact_tests[i][1])

for i in range(len(dr2l_tests)):
    verifier(f"DR2L test {i+1}", digits_r2l(dr2l_tests[i][0]), dr2l_tests[i][1])

for i in range(len(dl2r_tests)):
    verifier(f"DL2R test {i+1}", digits_l2r(dl2r_tests[i][0]), dl2r_tests[i][1])