import java.util.*;
import java.awt.*;
import javax.swing.*;

public class ChessBoard2 {

    // Instance variables.
    int size;
    int[] columns;   // column[r] = which column in row r has a queen, if any
                     // column[r] = -1, if this row has no queen


    // Constructor.

    public ChessBoard2 (int size) 
    {
        this.size = size;
        columns = new int [size];
        for (int i=0; i<size; i++) {
            columns[i] = -1;
        }
    }


    public int size ()
    {
        return size;
    }
    

    public String toString ()
    {
        String str = "Chessboard: \n";
        for (int i=0; i<size; i++) {
            if (columns[i] < 0) {
                for (int k=0; k<size; k++) {
                    str += " O";
                }
            }
            else {
                // columns[i]-1 blanks followed by X followed by (size-columns[i]-1) blanks.
                for (int k=0; k<=columns[i]-1; k++) {
                    str += " O";
                }
                str += " X";
                for (int k=columns[i]+1; k<size; k++) {
                    str += " O";
                }
            }
            str += "\n";
        }
        return str;
    }


    public void addQueen (int row, int col)
    {
        columns[row] = col;
    }
    

    public void removeQueen (int row, int col)
    {
        columns[row] = -1;
    }


    public boolean isForbidden (int row, int col)
    {
        // First, try the row.
        if (columns[row] >= 0) {
            return true;
        }
        
        // Now try the columns.
        for (int c=0; c<size; c++) {
            if (columns[row] == col) {
                return true;
            }
        }

        // Now the diagonals.
        for (int r=0; r<size; r++) {
            if (columns[r] >= 0) {
                if (Math.abs(columns[r]-col) == Math.abs(row-r)) {
                    return true;
                }
            }
        }
        
        return false;
    }

    public void display ()
    {
        // Make the frame and set some of its parameters:
        JFrame f = new JFrame ();
        f.setSize (300,300);
        f.setTitle ("N Queens problem");

        // Create our extension of the JPanel:
        ChessPanel drawPanel = new ChessPanel ();

        // We'll need to pass on the data:
        drawPanel.size = size;
        drawPanel.board = board;

        // Add this to the frame. Notice the strange syntax.
        f.getContentPane().add (drawPanel);

        // Bring up the frame.
        f.setVisible (true);
    }

}



class ChessPanel extends JPanel {
    
    int size;
    int[] columns;

    public void paintComponent (Graphics g)
    {
        // This is required.
        super.paintComponent (g);

        // First, compute the minimum dimension. The board size can't be larger.
        Dimension D = this.getSize();
        int minD = D.height;
        if (D.width < minD) {
            minD = D.width;
        }
        
        // This is the size of each square.
        int cellSize = minD / size;

        // We'll draw an image for each queen.
        ImageTool im = new ImageTool ();
        Image queen = im.readImageFile ("queen.jpg");
        
        // Now draw the chessboard.
        boolean isWhite = true;
        for (int i=0; i<size; i++) {
            for (int j=0; j<size; j++) {

                // Compute top-left.
                int topLeftX = j*cellSize;
                int topLeftY = i*cellSize;
                if (! isWhite) {
                    g.setColor (Color.gray);
                    g.fillRect (topLeftX, topLeftY, cellSize, cellSize);
                }
                g.setColor (Color.black);
                g.drawRect (topLeftX, topLeftY, cellSize, cellSize);

                // Alternate between black and white, except for end-of-row.
                if (j < size-1) {
                    isWhite = !isWhite;
                }

                if (columns[i] == j) {
                    // Draw the queen image.
                    g.drawImage (queen, topLeftX+1, topLeftY+1, cellSize-2, cellSize-2, null);
                }

            } // inner-for
        } // outer-for

    }

}