# 379 Design Phone Directory

### Problem:

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);
``````

### Solutions:

``````public class PhoneDirectory {
private HashSet<Integer> used;
private Queue<Integer> available;
/** Initialize your data structure here
@param maxNumbers - The maximum numbers that can be stored in the phone directory. */
public PhoneDirectory(int maxNumbers) {
used = new HashSet<Integer>();
for (int i = 0; i < maxNumbers; 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 (available.isEmpty()) {
return -1;
}
int next = available.poll();
return next;
}

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

/** Recycle or release a number. */
public void release(int number) {
if (used.contains(number)) {
used.remove((Integer) 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);
*/
``````
``````public class PhoneDirectory {
private int[] numbers;
private boolean[] used;
private int max;
private int next;
/** Initialize your data structure here
@param maxNumbers - The maximum numbers that can be stored in the phone directory. */
public PhoneDirectory(int maxNumbers) {
max = maxNumbers;
numbers = new int[max];
for (int i = 0; i < max; i ++) {
numbers[i] = i;
}
used = new boolean[max];
next = 0;
}

/** Provide a number which is not assigned to anyone.
@return - Return an available number. Return -1 if none is available. */
public int get() {
if (next < max) {
int result = numbers[next ++];
used[result] = true;
return result;
}
return -1;
}

/** Check if a number is available or not. */
public boolean check(int number) {
return number < max && number >= 0 && !used[number];
}

/** Recycle or release a number. */
public void release(int number) {
if (used[number]) {
next --;
numbers[next] = number;
used[number] = false;
}
}
}

/**
* 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);
*/
``````