```
class Solution(object):
def readBinaryWatch(self, num):
"""
:type num: int
:rtype: List[str]
"""
leds = [8, 4, 2, 1, 32, 16, 8, 4, 2, 1]
res = []
indices = itertools.combinations(range(10), num)
for index in indices:
hour = sum([leds[i] for i in index if i < 4])
minute = sum([leds[i] for i in index if i > 3])
if hour > 11 or minute > 59:
continue
res.append('{}:{:02d}'.format(hour, minute))
return res
```