Leetcode-401. Binary Watch

Description:

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.

Examples:

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".

C++ Solution:

class Solution {
public:
    vector<string> readBinaryWatch(int num) {
        vector<string> re;
        for(int h = 0; h < 12; h++)
        {
            for(int m = 0; m < 60; m++)
            {
                if(bitset<10>(h<<6
4000
|m).count() == num)
                {
                    re.emplace_back(to_string(h)+(m<10? ":0":":")+to_string(m));
                }
            }
        }
        return re;
    }
};