[LeetCode]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”.

2ms:

public List<String> readBinaryWatch(int num) {
String[][] hour = {{"0"},
{"1","2","4","8"},
{"3","5","6","9","10"},
{"7","11"}};
String[][] minute = {{"00"},//0
{"01","02","04","08","16","32"},//1
{"03","05","06","09","10","12","17","18","20","24","33","34","36","40","48"},//2
{"07","11","13","14","19","21","22","25","26","28","35","37","38","41","42","44","49","50","52","56"},//3
{"15","23","27","29","30","39","43","45","46","51","53","54","57","58"},//4
{"31","47","55","59"}//5

4000
};
List<String> result = new ArrayList<String>();
for(int i=0;i<=num&&i<hour.length;i++){
if((num-i)>=minute.length)
continue;
String[] h_ = hour[i];
String[] m_ = minute[num-i];
for(int j=0;j<h_.length;j++){
for(int k=0;k<m_.length;k++){
result.add(h_[j]+":"+m_[k]);
}
}
}
return result;
}