eightqueens.java

八皇后完全代码！显示图像

/*
 * @(#)EightQueens.java	1.0 2004-02-12
 *
 * Copyright 2004, will wang. All rights reserved.
 * email [e-mail]	[e-mail].
 */

import java.awt.*;
import java.awt.event.*;
import java.applet.*;

import java.util.Vector;

public class EightQueens extends Applet {
    Buttons buttons;   // The buttons for calculating and drawing queens
    CheeseCanvas canvas;       // The drawing area 
    Vector answers = new Vector();//
    Answer answer=new Answer();
     int x[]=new int[9];
    int answerNum;
    public void init() {
	setLayout(new BorderLayout());
	canvas = new CheeseCanvas();
	add("Center", canvas);
	add("South", buttons = new Buttons(this,canvas));
    }

    public void destroy() {
        remove(buttons);
        remove(canvas);
    }

    public void start() {
	buttons.setEnabled(true);
    }

    public void stop() {
	buttons.setEnabled(false);
    }

    public void processEvent(AWTEvent e) {
        if (e.getID() == Event.WINDOW_DESTROY) {
            System.exit(0);
        }
    }

    public static void main(String args[]) {
	Frame f = new Frame("EightQueens");
	EightQueens eightQueens = new EightQueens();

	eightQueens.init();
	eightQueens.start();

	f.add("Center", eightQueens);
	f.setSize(320, 320);
	f.show();
    }
    
    public String getAppletInfo() {
        return "EightQueens";
    }
    
    public int doCalculate()throws Exception{
	  int p[] = new int[9];
	  answers.removeAllElements();
	  for (int i = 0; i <= 8; i++)
	    x[i] = 0;
	  try{
	  	backTrack(1);
	  	return answers.size();
	  }catch(Exception exp) {
	  	return 0;
	}
    }
    boolean place(int k)
    {
     	int j;
	for (j = 1; j < k; j++)
	    if ((Math.abs(k - j) == Math.abs(x[j] - x[k])) || (x[j] == x[k])) return false;
	return true;
    }
     void backTrack(int t)
	{
	  if (t>8) {
	  	for (int j = 1; j <= 8; j++){
	  	answer.x[j-1]=x[j];
	}
	  	answers.add(answer);
	  	answer=new Answer();
	  	}
	  else for (int i = 1; i <= 8; i++){
	  	x[t]=i;
	  	if(place(t))backTrack(t+1);
	  	}
	  
	}
    public int showFirst(){
    	try{
    		answer=(Answer)answers.firstElement();
    		canvas.showAnswer(answer,1);
    		return 1;}
    	catch (Exception e){
    		return -1;
    	}
    }
    public int showPrevious(){
    	try{	
    		int index=answers.indexOf(answer) ;
    		if( index==0) return 0; 
    		answer=(Answer)answers.elementAt(index-1);
    		canvas.showAnswer(answer,index);
    		return 1;}
    	catch (Exception e){
    		return -1;
    	}
    }
    public int showNext(){
    	try{	
    		int index=answers.indexOf(answer) ;
    		if( index==answers.size()-1) return 0; 
    		answer=(Answer)answers.elementAt(index+1);
    		canvas.showAnswer(answer,index+2);
    		return 1;}
    	catch (Exception e){
    		return -1;
    	}
    }
    public int showLast(){
    	try{	
    		answer=(Answer)answers.lastElement();
    		canvas.showAnswer(answer,answers.size());
    		return 1;}
    	catch (Exception e){
    		return -1;
    	}
    }
}
class Answer{
    int x[];
    Answer(){
    	x=new int[8];
}
   	
}

class CheeseCanvas extends Canvas {
	Answer grid=null;
	int index=0;
    public void paint(Graphics g) {
	
	drawPanel();
	if (index>0)drawAnswer();
    }
    private void drawPanel(){
    	Graphics g=getGraphics();
    	int i,j;
	g.setColor(Color.black);
	for (i = 1; i <= 8; i++) {
	    for (j =1; j <= 8; j++) {
	    	if (((i+j)&1)==1){//奇数
	    	    g.fillRect((i-1)*40,(j-1)*40,40,40);
	    	}
	    }
	}   
	g.drawRect(0, 0, 320, 320);
    }
    public void showAnswer(Answer gg,int index){
    	grid=gg;
    	this.index=index;
    	repaint();
    	
    }
    
    private void drawAnswer(){
    	Graphics g=getGraphics();
    	int x,y;
    	if (grid==null) return;
    	g.setColor(Color.red);
    	g.drawString("index = " + index, 40, 350);
    	for (int i = 0; i < 8; i++) {    
	    x=(i)*40-15;y=(8-grid.x[i])*40;
	    g.drawLine(x+20,y+28,x+50,y+28);g.drawLine(x+20,y+25,x+15,y+15);
   	    g.drawLine(x+15,y+15,x+28,y+25);g.drawLine(x+28,y+25,x+28,y+10);
	    g.drawLine(x+28,y+10,x+35,y+25);g.drawLine(x+35,y+25,x+42,y+10);
	    g.drawLine(x+42,y+10,x+42,y+25);g.drawLine(x+42,y+25,x+55,y+15);
	    g.drawLine(x+55,y+15,x+50,y+25);
	     try {
                Thread.currentThread().sleep(300);
            } catch (InterruptedException e) {
            }
	    } 
    	}
}

class Buttons extends Panel
                  implements ActionListener {
    CheeseCanvas canvas;
    EightQueens myApp;
    Button bDoit,bFirst,bPrevious,bNext,bLast;
    public Buttons(EightQueens App,CheeseCanvas myCanvas) {
	this.myApp=App;
	this.canvas = myCanvas;
	
	bDoit = new Button("Do it!");
	bDoit.addActionListener(this);
	add(bDoit);
	
	bFirst = new Button("first");
	bFirst.addActionListener(this);
	add(bFirst);
	bFirst.setEnabled(false);
	
	bPrevious = new Button("previous");
	bPrevious.addActionListener(this);
	add(bPrevious);
	bPrevious.setEnabled(false);
	
	bNext = new Button("next");
	bNext.addActionListener(this);
	add(bNext);
	bNext.setEnabled(false);
	
	bLast = new Button("last");
	bLast.addActionListener(this);
	add(bLast);
	bLast.setEnabled(false);
    }

    public void actionPerformed(ActionEvent e) {
	String arg = e.getActionCommand();
	int i;
	try {
		if ("Do it!".equals(arg)) {
		    myApp.doCalculate();
		    if (myApp.showFirst()==1){
		    	bFirst.setEnabled(false);
    			bPrevious.setEnabled(false);
    			bNext.setEnabled(true);
    			bLast.setEnabled(true);
		    	}
		} else if ("first".equals(arg)) {
		    if (myApp.showFirst()==1){
		    	bFirst.setEnabled(false);
    			bPrevious.setEnabled(false);
    			bNext.setEnabled(true);
    			bLast.setEnabled(true);
		    	}
		} else if ("next".equals(arg)) {
		    if (myApp.showNext()==0){
    			bNext.setEnabled(false);
    			bLast.setEnabled(false);
    		    }else{
    		    	bFirst.setEnabled(true);
    			bPrevious.setEnabled(true);
    		        bNext.setEnabled(true);
    			bLast.setEnabled(true);
		    	}
		} else if ("previous".equals(arg)) {
		    if (myApp.showPrevious()==0){
		    	bFirst.setEnabled(false);
    			bPrevious.setEnabled(false);
    		   }else{
    			bFirst.setEnabled(true);
    			bPrevious.setEnabled(true);
    			bNext.setEnabled(true);
    			bLast.setEnabled(true);
		    	}
		} else if ("last".equals(arg)) {
		    if (myApp.showLast()==1){
		    	bFirst.setEnabled(true);
    			bPrevious.setEnabled(true);
    			bNext.setEnabled(false);
    			bLast.setEnabled(false);
		    	}
		} else {
		    
		}
	} catch(Exception exp) {
	}
    }
}