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Design Phone Directory

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Description

Solution

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class PhoneDirectory {
public:
    unordered_map<int, list<int>::iterator > setting;
    list<int> lis;
    /** 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) {
            lis.push_back(i);
            setting[i] = lis.begin();
        }
    }
    
    /** Provide a number which is not assigned to anyone.
        @return - Return an available number. Return -1 if none is available. */
    int get() {
        if (lis.empty()) return -1;
        int ret = *(lis.begin());
        setting.erase(ret);
        lis.pop_front();
        return ret;
    }
    
    /** Check if a number is available or not. */
    bool check(int number) {
        return setting.find(number) != setting.end();
    }
    
    /** Recycle or release a number. */
    void release(int number) {
        if (setting.count(number) != 0) return;
        lis.push_front(number);
        setting[number] = lis.begin();
    }
};

/**
 * 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);
 */