[CareerCup] 8.4 Parking Lot 停車場問題

 

8.4 Design a parking lot using object-oriented principles.

 

LintCode上的原題，請參見我的另一篇博客Parking Lot 停車場問題。

這道題讓我們實現一個停車位的數據結構，由於題目沒給任何多余的信息，所以自由度很大，比如能停放什么種類的車，或是否是多層的等等。根據書中描述，這里我們做如下假設：

1. 停車場有多層，每層有多行停車位

2. 停車場可以停摩托車，小轎車和公交車

3. 停車場有摩托車位，緊湊型車位，和大型車位

4. 摩托車可以停在任何位置

5. 小轎車可以停在緊湊型車位和大型車位

6. 公交車只能停在同一行中連續的五個大型車位上，不能停在小位置上

有了這么多條件，我們就可以開始寫各種類了。首先可定要有個基本類Vehicle，然后摩托車，小轎車和公交車都可以派生出來，每個派生類和基類不同的是需要的空位數不同，還有就是車型不同，那么就要把基類的判斷是否能停在當前位置設為虛函數，在派生類中分別實現出來。我們還要用枚舉類VehicleSize來標識車型。然后就是要有停車場類ParkingLot，層類Level，停車位類ParkingSpot，它們之間錯綜復雜的關系請參見下列代碼：

 

enum class VehicleSize { Motorcycle, Compact, Large };

class Vehicle;
class Level;

class ParkingSpot {
public:
    ParkingSpot(Level *lvl, int r, int n, VehicleSize s): _level(lvl), _row(r), _spotNumber(n), _spotSize(s) {} // ...
    bool isAvailable() { return _vehicle == nullptr; };
    bool canFitVehicle(Vehicle *vehicle) {} // ...
    bool park(Vehicle *v) {} // ...
    int getRow() { return _row; }
    int getSpotNumber() { return _spotNumber; }
    void removeVehicle() {} // ... 

private:
    Vehicle *_vehicle = nullptr;
    VehicleSize _spotSize;
    int _row;
    int _spotNumber;
    Level *_level = nullptr;
};

class Vehicle {
public:
    Vehicle() {}
    int getSpotsNeeded() { return _spotsNeeded; }
    VehicleSize getSize() { return _size; }
    void parkInSpot(ParkingSpot s) { _parkingSpots.push_back(s); }
    void clearSpots() {} // ...
    virtual bool canFitInSpot(ParkingSpot spot) {}

protected:
    vector<ParkingSpot> _parkingSpots;
    string _licensePlate;
    int _spotsNeeded;
    VehicleSize _size;
};

class Bus: public Vehicle {
public:
    Bus() {
        _spotsNeeded = 5;
        _size = VehicleSize::Large;
    }
    bool canFitInSpot(ParkingSpot spot) { }
};

class Car: public Vehicle {
public:
    Car() {
        _spotsNeeded = 1;
        _size = VehicleSize::Compact;
    }
    bool canFitInSpot(ParkingSpot spot) { }
};

class Motorcycle: public Vehicle {
public:
    Motorcycle() {
        _spotsNeeded = 1;
        _size = VehicleSize::Motorcycle;
    }
    bool canFitInSpot(ParkingSpot spot) { }
};

class Level {
public:
    Level() {}
    Level(int flr, int numberSpots): _floor(flr), _availableSpots(numberSpots) {}
    Level(const Level* lvl) {
        *this = *lvl;
    }
    int availableSpots() { return _availableSpots; }
    bool parkVehicle(Vehicle vehicle) {} // ...
    void spotFreed() { ++_availableSpots; }

private:
    int _floor;
    vector<ParkingSpot> _spots;
    int _availableSpots = 0;
    static const int _SPOTS_PER_ROW = 10;
    bool parkStartingAtSpot(int num, Vehicle v) {} // ...
    int findAvailableSpots(Vehicle vehicle) {} // ...
};

class ParkingLot {
public:
    ParkingLot() {} // ...
    bool parkVehicle(Vehicle vehicle) {} // ...

private:
    vector<Level> _levels;
    const int _NUM_LEVELS = 5;
};