Binary Watch

//401
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.

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".

#include <iostream>
#include <vector>
#include <bitset>
#include <string>

using namespace std;

class Solution {
public:
    vector<string> readBinaryWatch(int num) {
        //permutation
        vector<string> res;
        for(int h=0;h<12;h++){
            for(int m=0;m<60;m++){
                if(bitset<10>(h<<6 | m).count()==num){
                    //left move,right->left become empty
                    //becom 10 bit h--4 bit ，m--6 bit
                    res.push_back(to_string(h)+(m<10 ? ":0":":")+to_string(m));
                }
            }
        }
        return res;
    }
};

int main(){
    int num=1;
    vector<string> res;
    res=Solution().readBinaryWatch(num);
    for(int i=0;i<res.size();i++){
        for(int j=0;j<res[i].size();j++){
            cout<<res[i][j]<<" ";
        }
        cout<<endl;
    }
    return 0;
}