379. Design Phone Directory

• Difficulty: Medium

• Topics: Linked List, Design

• Similar Questions:

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); </pre> </p>

Solutions:

class PhoneDirectory {
public:
    /** Initialize your data structure here
        @param maxNumbers - The maximum numbers that can be stored in the phone directory. */
    PhoneDirectory(int maxNumbers) {
        for (int i = 0; i < maxNumbers; ++i) {
            phones.insert(i);
        }
    }

    /** Provide a number which is not assigned to anyone.
        @return - Return an available number. Return -1 if none is available. */
    int get() {
        auto it = phones.begin(); // constant time complexity
        if (it == phones.end()) {
            return -1;
        }

        int val = *it;
        phones.erase(it);
        return val;
    }

    /** Check if a number is available or not. */
    bool check(int number) {
        return phones.count(number) > 0;
    }

    /** Recycle or release a number. */
    void release(int number) {
        phones.insert(number);
    }
private:
    unordered_set<int> phones;

};

/**
 * Your PhoneDirectory object will be instantiated and called as such:
 * PhoneDirectory* obj = new PhoneDirectory(maxNumbers);
 * int param_1 = obj->get();
 * bool param_2 = obj->check(number);
 * obj->release(number);
 */