Leetcode: Design Phone Directory

Design a Phone Directory which supports the following operations:

get: Provide a number which is not assigned to anyone.
check: Check if a number is available or not.
release: Recycle or release a number.
Example:

// Init a phone directory containing a total of 3 numbers: 0, 1, and 2.
PhoneDirectory directory = new PhoneDirectory(3);

// It can return any available phone number. Here we assume it returns 0.
directory.get();

// Assume it returns 1.
directory.get();

// The number 2 is available, so return true.
directory.check(2);

// It returns 2, the only number that is left.
directory.get();

// The number 2 is no longer available, so return false.
directory.check(2);

// Release number 2 back to the pool.
directory.release(2);

// Number 2 is available again, return true.
directory.check(2);

my HashSet+ ArrayList, 删除的时候把要删的index与末尾对调。get()其实不需要random, 因为anyone is ok

 public class PhoneDirectory {
     ArrayList<Integer> arr;
     HashSet<Integer> set;

     /** Initialize your data structure here
         @param maxNumbers - The maximum numbers that can be stored in the phone directory. */
     public PhoneDirectory(int maxNumbers) {
         arr = new ArrayList<Integer>();
         set = new HashSet<Integer>();
         for (int i=0; i<maxNumbers; i++) {
             arr.add(i);
             set.add(i);
         }
     }

     /** Provide a number which is not assigned to anyone.
         @return - Return an available number. Return -1 if none is available. */
     public int get() {
         if (arr.size() == 0) return -1;
         Random random = new Random();
         int index = random.nextInt(arr.size());
         int temp = arr.get(index);
         arr.set(index, arr.get(arr.size()-1));
         arr.set(arr.size()-1, temp);
         arr.remove(arr.size()-1);
         set.remove(temp);
         return temp;
     }

     /** Check if a number is available or not. */
     public boolean check(int number) {
         return set.contains(number);
     }

     /** Recycle or release a number. */
     public void release(int number) {
         if (!set.contains(number)) {
             arr.add(number);
             set.add(number);
         }
     }
 }

 /**
  * Your PhoneDirectory object will be instantiated and called as such:
  * PhoneDirectory obj = new PhoneDirectory(maxNumbers);
  * int param_1 = obj.get();
  * boolean param_2 = obj.check(number);
  * obj.release(number);
  */

HashSet+ Queue网上vote最高的solution,

 public class PhoneDirectory {

     Set<Integer> used = new HashSet<Integer>();
     Queue<Integer> available = new LinkedList<Integer>();
     int max;
     public PhoneDirectory(int maxNumbers) {
         max = maxNumbers;
         for (int i = 0; i < maxNumbers; i++) {
             available.offer(i);
         }
     }

     public int get() {
         Integer ret = available.poll();
         if (ret == null) {
             return -1;
         }
         used.add(ret);
         return ret;
     }

     public boolean check(int number) {
         if (number >= max || number < 0) {
             return false;
         }
         return !used.contains(number);
     }

     public void release(int number) {
         if (used.remove(number)) {
             available.offer(number);
         }
     }
 }

 /**
  * Your PhoneDirectory object will be instantiated and called as such:
  * PhoneDirectory obj = new PhoneDirectory(maxNumbers);
  * int param_1 = obj.get();
  * boolean param_2 = obj.check(number);
  * obj.release(number);
  */