Leetcode: Design Phone Directory

 1 public class PhoneDirectory { 2     ArrayList<Integer> arr; 3     HashSet<Integer> set; 4  5     /** Initialize your data structure here 6         @param maxNumbers - The maximum numbers that can be stored in the phone directory. */ 7     public PhoneDirectory(int maxNumbers) { 8         arr = new ArrayList<Integer>(); 9         set = new HashSet<Integer>();10         for (int i=0; i<maxNumbers; i++) {11             arr.add(i);12             set.add(i);13         }14     }15     16     /** Provide a number which is not assigned to anyone.17         @return - Return an available number. Return -1 if none is available. */18     public int get() {19         if (arr.size() == 0) return -1;20         Random random = new Random();21         int index = random.nextInt(arr.size());22         int temp = arr.get(index);23         arr.set(index, arr.get(arr.size()-1));24         arr.set(arr.size()-1, temp);25         arr.remove(arr.size()-1);26         set.remove(temp);27         return temp;28     }29     30     /** Check if a number is available or not. */31     public boolean check(int number) {32         return set.contains(number);33     }34     35     /** Recycle or release a number. */36     public void release(int number) {37         if (!set.contains(number)) {38             arr.add(number);39             set.add(number);40         }41     }42 }43 44 /**45  * Your PhoneDirectory object will be instantiated and called as such:46  * PhoneDirectory obj = new PhoneDirectory(maxNumbers);47  * int param_1 = obj.get();48  * boolean param_2 = obj.check(number);49  * obj.release(number);50  */

 1 public class PhoneDirectory { 2  3     Set<Integer> used = new HashSet<Integer>(); 4     Queue<Integer> available = new LinkedList<Integer>(); 5     int max; 6     public PhoneDirectory(int maxNumbers) { 7         max = maxNumbers; 8         for (int i = 0; i < maxNumbers; i++) { 9             available.offer(i);10         }11     }12     13     public int get() {14         Integer ret = available.poll();15         if (ret == null) {16             return -1;17         }18         used.add(ret);19         return ret;20     }21     22     public boolean check(int number) {23         if (number >= max || number < 0) {24             return false;25         }26         return !used.contains(number);27     }28     29     public void release(int number) {30         if (used.remove(number)) {31             available.offer(number);32         }33     }34 }35 36 /**37  * Your PhoneDirectory object will be instantiated and called as such:38  * PhoneDirectory obj = new PhoneDirectory(maxNumbers);39  * int param_1 = obj.get();40  * boolean param_2 = obj.check(number);41  * obj.release(number);42  */