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.

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"]

Approach:

C++

#include <bits/stdc++.h>
using namespace std;

vector<string> readBinaryWatch(int num)
{
    vector<string> res;
    char str[10];
    for (int i = 0; i < 1 << 10; i++)
    {
        int s = 0;
        for (int j = 0; j < 10; j++)
        {
            if (i >> j & 1)
            {
                s++;
            }
        }
        if (s == num)
        {
            int a = i >> 6, b = i & 63;
            if (a < 12 && b < 60)
            {

                string str = "";
                if (b < 10)
                    str = str + to_string(a) + ":" + "0" + 
               to_string(b);
                else
                    str = str + to_string(a) + ":" +
                     to_string(b);

                res.push_back(str);
            }
        }
    }
    return res;
}

int main()
{
    int n = 1;

    vector<string> res = readBinaryWatch(n);

    cout << "[";
    for (int i = 0; i < res.size(); i++)
    {
        cout << res[i];
        if (i != res.size() - 1)
            cout << ",";
    }
    cout << "]";

    return 0;
}