## 题目描述：

LeetCode 401. Binary Watch

A binary watch has 4 LEDs on the top which represent the hours (0-11), and the 6 LEDs on the bottom represent the minutes (0-59).

Each LED represents a zero or one, with the least significant bit on the right.

For example, the above binary watch reads "3:25".

Given a non-negative integer n which represents the number of LEDs that are currently on, return all possible times the watch could represent.

Example:

```Input: n = 1
Return: ["1:00", "2:00", "4:00", "8:00", "0:01", "0:02", "0:04", "0:08", "0:16", "0:32"]```

Note:

• The order of output does not matter.
• The hour must not contain a leading zero, for example "01:00" is not valid, it should be "1:00".
• The minute must be consist of two digits and may contain a leading zero, for example "10:2" is not valid, it should be "10:02".

## 解题思路：

10盏灯泡的燃亮情况可以通过0-1024进行表示，然后计数二进制1的个数即可。

## Python代码：

``````class Solution(object):
"""
:type num: int
:rtype: List[str]
"""
ans = []
for x in range(1024):
if bin(x).count('1') == num:
h, m = x >> 6, x & 0x3F
if h < 12 and m < 60:
ans.append('%d:%02d' % (h, m))
return ans
``````

## Python代码：

``````class Solution(object):
"""
:type num: int
:rtype: List[str]
"""
ans = []
for h in range(12):
for m in range(60):
if (bin(h)+ bin(m)).count('1') == num:
ans.append('%d:%02d' % (h, m))
return ans
``````

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