Circle selection in an Integer[][] matrix - Java [closed]

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I have a matrix with n columns, n rows and every element is initialized with 0.

I want to select the largest circle in that matr开发者_C百科ix, and set the values to 1.

000010000
000111000
000111000
001111100
011111110     The drawing isnt't very artistic (or correct)...  
001111100        matrix: 9*9
000111000        largest circle
000111000
000010000

Can you help me with the java algorithm ?

Language: Java

Thank you, Horatiu

---

The most efficient way to find proper pixels of a circle boundary is the Bresenhamn's algorithm or Mid Point Circle Algorithm; http://en.wikipedia.org/wiki/Midpoint_circle_algorithm#Optimization

this is how I change that to fit yours:

public class Circle {
    private char[][] px;
    private char cEmpty='.';
    private char cFilled='#';
    public static void main(String[] args) {
        new Circle(15);
    }
    public Circle(int size)
    {
        px=new char[size][size];
        for(int i=0;i<size;i++)
            for(int j=0;j<size;j++)
                px[i][j]=cEmpty;
        calc(size/2,size/2,size/2-1);
        for(int i=0;i<size;i++){
            for(int j=0;j<size;j++)
                System.out.print(px[i][j]);
            System.out.println();
        }
    }

    public void calc(int cx, int cy, int radius)
    {
      int error = -radius;
      int x = radius;
      int y = 0;
      while (x >= y)
      {
        plot8points(cx, cy, x, y);   
        error += y;
        ++y;
        error += y;
        if (error >= 0)
        {
          --x;
          error -= x;
          error -= x;
        }
      }
    }

    void plot8points(int cx, int cy, int x, int y)
    {
      plot4points(cx, cy, x, y);
      if (x != y) plot4points(cx, cy, y, x);
    }
    void plot4points(int cx, int cy, int x, int y)
    {
      setPixel(cx + x, cy + y);
      if (x != 0) setPixel(cx - x, cy + y);
      if (y != 0) setPixel(cx + x, cy - y);
      if (x != 0 && y != 0) setPixel(cx - x, cy - y);
    }
    void setPixel(int x, int y){
        px[x][y]=cFilled;
    }
}

---

Here's a naive algorithm. It fills in each point to a 0 or 1 depending upon whether it lies inside or outside the circle.

public static void main(String[] args)
{
    int[][] matrix = new int[9][];
    double midPoint = (matrix.length-1)/2.0;
    for (int col = 0; col < matrix.length; col++)
    {
        int[] row = new int[matrix.length];
        double yy = col-midPoint;
        for (int x=0; x<row.length; x++)
        {
           double xx = x-midPoint;
           if (Math.sqrt(xx*xx+yy*yy)<=midPoint)
             row[x] = 1;
           System.out.print(row[x]);
        }
        matrix[col] = row;
        System.out.println();
    }

}