[LintCode][System Design] Shape Factory

Problem

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

Example

ShapeFactory sf = new ShapeFactory();
Shape shape = sf.getShape("Square");
shape.draw();

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|    |
|    |
 ----

shape = sf.getShape("Triangle");
shape.draw();

  /\
 /  \
/____\

shape = sf.getShape("Rectangle");
shape.draw();

 ----
|    |
 ----

Solution

class Shape {
public:
    virtual void draw() const=0;

    void drawHorizontalLine() const {
        drawSpace(1);
        for(int i = 0; i < 4; i++) {
            cout << '-';
        }
        drawSpace(1);
        cout << endl;
    }

    void drawVerticalLine() const {
        cout << '|';
        drawSpace(4);
        cout << '|' << endl;
    }

    void drawSpace(int n) const {
        for(int i = 0; i < n; i++) {
            cout << ' ';
        }
    }
};

class Rectangle: public Shape {
public:
    void draw() const {
        drawHorizontalLine();
        drawVerticalLine();
        drawHorizontalLine();
    }
};

class Square: public Shape {
public:
    void draw() const {
        drawHorizontalLine();
        drawVerticalLine();
        drawVerticalLine();
        drawHorizontalLine();
    }
};

class Triangle: public Shape {
public:
    void draw() const {
        drawSpace(2);
        cout << "/\\" << endl;
        drawSpace(1);
        cout << '/';
        drawSpace(2);
        cout << '\\' << endl;
        cout << '/';
        for(int i = 0; i < 4; i++) {
            cout << '_';
        }
        cout << '\\' << endl;
    }
};

class ShapeFactory {
private:
    const string squareType = "Square";
    const string triangleType = "Triangle";
    const string rectType = "Rectangle";

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

        return NULL;
    }
};