Design Phone Directory

 1 public class PhoneDirectory {
 2     private boolean[] nums;
 3     private Queue<Integer> queue;
 4     /** Initialize your data structure here
 5         @param maxNumbers - The maximum numbers that can be stored in the phone directory. */
 6     public PhoneDirectory(int maxNumbers) {
 7         nums = new boolean[maxNumbers];
 8         queue = new LinkedList<>();
 9         for (int i = 0; i < maxNumbers; i++) {
10             queue.offer(i);
11         }
12     }
13
14     /** Provide a number which is not assigned to anyone.
15         @return - Return an available number. Return -1 if none is available. */
16     public int get() {
17         if (queue.isEmpty()) {
18             return -1;
19         }
20         int result = queue.poll();
21         nums[result] = true;
22         return result;
23     }
24
25     /** Check if a number is available or not. */
26     public boolean check(int number) {
27         return !nums[number];
28     }
29
30     /** Recycle or release a number. */
31     public void release(int number) {
32         if (!nums[number]) {
33             return;
34         }
35         nums[number] = false;
36         queue.offer(number);
37     }
38 }
39
40 /**
41  * Your PhoneDirectory object will be instantiated and called as such:
42  * PhoneDirectory obj = new PhoneDirectory(maxNumbers);
43  * int param_1 = obj.get();
44  * boolean param_2 = obj.check(number);
45  * obj.release(number);
46  */