379. Design Phone Directory

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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:

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// 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);

解法1：

用一个hashset存储号码。get的时候用directory.iterator().next()来得到下一个数字。
C++

1

Java

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public class PhoneDirectory {
    HashSet<Integer> directory;
    /** Initialize your data structure here
        @param maxNumbers - The maximum numbers that can be stored in the phone directory. */
    public PhoneDirectory(int maxNumbers) {
        directory = new HashSet<Integer>();
        for (int i = 0; i < maxNumbers; i++) {
            directory.add(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 (directory.size() == 0) {
            return -1;
        }
        int key = directory.iterator().next();
        directory.remove(key);
        return key;
    }
    /** Check if a number is available or not. */
    public boolean check(int number) {
        return directory.contains(number);
    }
    /** Recycle or release a number. */
    public void release(int number) {
        directory.add(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);
 */