Binary Watch

问题：

A binary watch has 4 LEDs on the top which represent the hours (0-11), and the 6 LEDs on the bottom represent theminutes (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 = 1Return: ["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".

代码：

class Solution {public:    vector<string> readBinaryWatch(int num) {                vector<string> ans;        for(int i=0; i<12; i++)        {            for(int j=0; j<60; j++)            {                int temp=bitset<10>(i).count()+bitset<10>(j).count();                if(temp==num)                {                    string tmp;                    tmp=to_string(i) + (j < 10 ? ":0" : ":") + to_string(j);                    ans.push_back(tmp);                }            }        }        return ans;    }};

分析：

数据量较小容易遍历，学习到一点就时位操作，计算一个数字二进制形式中1的个数，使用函数bitset<10>(i).count()来计算