8.4 Design a parking lot using object-oriented principles.

 

LintCode上的原题，请参见我的另一篇博客Parking Lot 停车场问题。

这道题让我们实现一个停车位的数据结构，由于题目没给任何多余的信息，所以自由度很大，比如能停放什么种类的车，或是否是多层的等等。根据书中描述，这里我们做如下假设：

1. 停车场有多层，每层有多行停车位

2. 停车场可以停摩托车，小轿车和公交车

3. 停车场有摩托车位，紧凑型车位，和大型车位

4. 摩托车可以停在任何位置

5. 小轿车可以停在紧凑型车位和大型车位

6. 公交车只能停在同一行中连续的五个大型车位上，不能停在小位置上

有了这么多条件，我们就可以开始写各种类了。首先可定要有个基本类Vehicle，然后摩托车，小轿车和公交车都可以派生出来，每个派生类和基类不同的是需要的空位数不同，还有就是车型不同，那么就要把基类的判断是否能停在当前位置设为虚函数，在派生类中分别实现出来。我们还要用枚举类VehicleSize来标识车型。然后就是要有停车场类ParkingLot，层类Level，停车位类ParkingSpot，它们之间错综复杂的关系请参见下列代码：

 

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 _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 _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 _levels;

const int _NUM_LEVELS = 5;

};

 

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