Question

I am supposed to modified this Sierpinski’s triangle program to count the number of triangles. So i tried to increment count every time it make a triangle, but, somehow my count doesn’t increment.

public class SierpinskiTriangle extends Applet 
{  

    public int SeirpTri(Graphics g, int x1, int y1, int x2, int y2, int x3, int y3, int n, int count)  
    {
        this.setBackground(new Color(0,0,0));
        this.setSize(700, 500);
        if ( n == 0 )
        {
            g.setColor(new Color(0, 255, 0));
            g.drawLine(x1, y1, x2, y2);     // if n = 0 draw the triangle
            g.drawLine(x2, y2, x3, y3);
            g.drawLine(x3, y3, x1, y1);        
            return 1;     
        }

        int xa, ya, xb, yb, xc, yc;   // make 3 new triangles by connecting the midpoints of
        xa = (x1 + x2) / 2;             //. the previous triangle 
        ya = (y1 + y2) / 2;
        xb = (x1 + x3) / 2;
        yb = (y1 + y3) / 2;
        xc = (x2 + x3) / 2;
        yc = (y2 + y3) / 2; 
        SeirpTri(g, x1, y1, xa, ya, xb, yb, n - 1, count++);   // recursively call the function using the 3 triangles
        SeirpTri(g, xa, ya, x2, y2, xc, yc, n - 1, count++);
        SeirpTri(g, xb, yb, xc, yc, x3, y3, n - 1, count++);
        return count;
    }

    public void paint(Graphics g)    
    {
        int recursions = 3;
        int count=1;
        // call the recursive function sending in the number of recursions
        SeirpTri(g, 319, 0, 0, 479, 639, 479, recursions, count);

        // Counting triangles using math algorithm;
        int count2 = 1;
        if (recursions ==0) {
            count2 =1;
        }
        else {
            count2 = (int) Math.pow(3,(recursions-1)) * 3;
        }
        System.out.println("Correct answer is: " +count2);
        System.out.println("Answer using recurvise is: " +count*3);
    }        
}

Answer 1

You return count, but never look at the result of calling SeirpTri.

Instead of:

SeirpTri(g, x1, y1, xa, ya, xb, yb, n - 1, count++);   // recursively call the function using the 3 triangles
SeirpTri(g, xa, ya, x2, y2, xc, yc, n - 1, count++);
SeirpTri(g, xb, yb, xc, yc, x3, y3, n - 1, count++);
return count;

try something like:

return
    SeirpTri(g, x1, y1, xa, ya, xb, yb, n - 1)
    + SeirpTri(g, xa, ya, x2, y2, xc, yc, n - 1)
    + SeirpTri(g, xb, yb, xc, yc, x3, y3, n - 1);

You don’t need the count parameter at all. Each SeirpTri invocation only needs to know aboult the triangles it and its “children” (on the call tree) have created. The “root” call (in paint) will return the grand total.