[LintCode] Shape Factory 形状工厂

Factory is a design pattern in common usage. Implement a ShapeFactory that can generate correct shape.

You can assume that we have only tree different shapes: Triangle, Square and Rectangle.

Example

ShapeFactory sf = new ShapeFactory();

Shape shape = sf.getShape("Square");

shape.draw();

>>  ----

>> |    |

>> |    |

>>  ----

shape = sf.getShape("Triangle");

shape.draw();

>>   /\

>>  /  \

>> /____\

shape = sf.getShape("Rectangle");

shape.draw();

这道题让我们求形状工厂，实际上就是Factory pattern的一个典型应用，说得是有一个基类Shape，然后派生出矩形，正方形，和三角形类，每个派生类都有一个draw，重写基类中的draw，然后分别画出派生类中的各自的形状，然后在格式工厂类中提供一个派生类的字符串，然后可以新建对应的派生类的实例，没啥难度，就是考察基本的知识。

class Shape {
public:
    virtual void draw() const=;
};

class Rectangle: public Shape {
public:
    void draw() const {
        cout << " ---- " << endl;
        cout << "|    |" << endl;
        cout << " ---- " << endl;
    }
};

class Square: public Shape {
public:
    void draw() const {
        cout << " ---- " << endl;
        cout << "|    |" << endl;
        cout << "|    |" << endl;
        cout << " ---- " << endl;
    }
};

class Triangle: public Shape {
public:
    void draw() const {
        cout << "  /\\ " << endl;
        cout << " /  \\ " << endl;
        cout << "/____\\ " << endl;
    }
};

class ShapeFactory {
public:
    /**
     * @param shapeType a string
     * @return Get object of type Shape
     */
    Shape* getShape(string& shapeType) {
        if (shapeType == "Square") return new Square();
        else if (shapeType == "Triangle") return new Triangle();
        else if (shapeType == "Rectangle") return new Rectangle();
        else return NULL;
    }
};