# Binary Watch

Binary Watch bit manipulation

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.

``````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"]
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".
``````

Binary Watch Solution

``````public class BinaryWatch {
ArrayList<String> allTimes = new ArrayList<String>();

//iterate through all possible time combinations
for(int i = 0; i < 12; i++) {
for(int j = 0; j < 60; j++) {
//if the current number and n have the same number of bits the time is possible
if(Integer.bitCount(i * 64 + j) == num) {
//add the current time to all times arraylist