(LeetCode)Binary Watch --- 二进制手表

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".

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解题分析：

 题意大概是一个二进制手表的表盘一共有两行指示灯，第一行表示（0 -- 11）小时的信息，第二行表示（0 -- 59）分钟的信息。

输入数字，表示亮灯的数量，然后可以计算二进制中1的个数，转换位置，来计算所有可能性。

解法一：位运算

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

解法二：遍历所有：

    

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