379. 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);

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);

}

}