379. Design Phone Directory

JIAKAOBO

LeetCode

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Problem

Design a Phone Directory which supports the following operations:

1. get: Provide a number which is not assigned to anyone.
2. check: Check if a number is available or not.
3. 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);

Code

class PhoneDirectory {
    HashSet<Integer> set;
    Queue<Integer> queue;
    public PhoneDirectory(int maxNumbers) {
        set = new HashSet<>();
        queue = new LinkedList<>();
        for(int i = 0; i < maxNumbers; i++){
            set.add(i);
            queue.add(i);
        }
    }

    public int get() {
        if(queue.size() != 0){
            int num = queue.poll();
            set.remove(num);
            return num;
        } else {
            return -1;
        }
    }

    public boolean check(int number) {
        return set.contains(number);
    }

    public void release(int number) {
        if(set.add(number)){
            queue.offer(number);
        }
    }
}

class PhoneDirectory {
    int maxNumbers;
    HashSet<Integer> set;
    public PhoneDirectory(int maxNumbers) {
        this.maxNumbers = maxNumbers;
        // set中放已经在用的数字
        set = new HashSet<>();
    }

    public int get() {
        for(int i = 0; i < maxNumbers; i++) {
            if(!set.contains(i)) {
                set.add(i);
                return i;
            }
        }

        return -1;
    }

    public boolean check(int number) {
        return !set.contains(number);
    }

    public void release(int number) {
        if(set.contains(number)) {
            set.remove(number);
        }
    }
}