401. 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 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 = 1
Return: ["1:00", "2:00", "4:00", "8:00", "0:01", "0:02", "0:04", "0:08", "0:16", "0:32"]

public class Solution {    public List<String> readBinaryWatch(int num) {        List<String> s=new ArrayList<>();        for(int h=0;h<12;h++)        {            for(int m=0;m<60;m++)            {                if(Integer.bitCount(h*64+m)==num)                {                    s.add(String.format("%d:%02d",h,m));                }            }        }        return s;    }}