不重复的三位数

# 有1、2、3、4个数字，能组成多少个互不相同且无重复数字的三位数？都是多少？

def three_number():
    ll = [1, 2, 3, 4]
    count = 0
    for a in ll:
        for b in ll:
            for c in ll:
                if (a != b) and (a != c) and (b != c):
                    count += 1
                    print('{}{}{}'.format(a, b, c))
    return count