精通算法系列-二进制手表

原题为:

// 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".

答案如下：

public class Solution {    public List<String> readBinaryWatch(int num) {        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                    allTimes.add(String.format("%d:%02d", i, j));                }            }        }        return allTimes;    }}