```
public class PhoneDirectory {
private boolean[] numbers;
private int index = 0;
private Deque<Integer> stack;
/** Initialize your data structure here
@param maxNumbers - The maximum numbers that can be stored in the phone directory. */
public PhoneDirectory(int maxNumbers) {
numbers = new boolean[maxNumbers] ;
Arrays.fill(numbers, true);
stack = new ArrayDeque<Integer>();
for(int i = 0; i < maxNumbers; i++) {
stack.push(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(stack.size() == 0)
return -1;
int number = stack.pop();
numbers[number] = false;
return number;
}
/** Check if a number is available or not. */
public boolean check(int number) {
return numbers[number];
}
/** Recycle or release a number. */
public void release(int number) {
if(!numbers[number]) {
numbers[number] = true;
stack.push(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);
*/
```