LeetCode_401. Binary Watch

401. Binary Watch

Easy

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".

package leetcode.easy;

public class BinaryWatch {
	public java.util.List<String> readBinaryWatch(int num) {
		java.util.List<String> ret = new java.util.ArrayList<>(1024);

		for (int hour = 0; hour < 12; ++hour) {
			for (int min = 0; min < 60; ++min) {
				if (Integer.bitCount(hour) + Integer.bitCount(min) == num) {
					ret.add(String.format("%d:%02d", hour, min));
				}
			}
		}

		return ret;
	}

	@org.junit.Test
	public void test() {
		System.out.println(readBinaryWatch(1));
	}
}