[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=0;
};

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;
    }
};