输出由1，2，3，4组成的互不相同且无重复的三位数！
#方式一
lst = ['1', '2', '3', '4']
res = []
for i in lst:
for j in lst:
for k in lst:
# print(set(i + j + k))
if len(set(i + j + k)) == 3:
print(set(i + j + k))
res.append(int(i + j + k))
print(res)
print(len(res))
#方式二
count = 0
for i in range(1, 5):
for j in range(1, 5):
for k in range(1, 5):
if (i != j) and (i != k) and (j != k):
count += 1
print(count)
#方式三
lst = "1234”
res = 0
for i in lst:
for j in lst:
for k in lst:
# print(set(i + j + k))
if len(set(i + j + k)) == 3:
print(set(i + j + k))
res += 1
print(res)
#a 与 b必须是两个相同类型的可迭代对象
a = "1"
b = "2"
print(set(a + b)) # {'1', '2'}
a = "123"
b = "2"
print(set(a + b)) # {'1', '2', '3'}
a = ['1', '3', 2]
b = ['2']
print(set(a + b)) # {'2', '3', 2, '1'}