# 379.Design-Phone-Directory

## 379. Design Phone Directory

## 题目地址

[https://leetcode.com/problems/design-phone-directory/](https://leetcode.com/problems/design-phone-directory/)

## 题目描述

```
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);
```

## 代码

### Approach #1

```java
class PhoneDirectory {

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

  /** Provide a number which is not assigned to anyone.
      @return - Return an available number. Return -1 if none is available. */
  public int get() {
        Integer ret = queue.poll();
    if (ret == null)    return -1;
    used.add(ret);
    return ret;
  }

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

  /** Recycle or release a number. */
  public void release(int number) {
        if (used.remove(number)) {
      queue.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);
*/
```
