379. Design Phone Directory
Tags: ‘Linked List’, ‘Design’
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);
Solution
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);
}
}
}