八皇后問題，都知道吧。循環套遞歸，比漢諾塔還寒，暈歸暈，索性弄出來了，撒花~~~


public class Das_n_Damen_Problem extends ChessMiniJava{
??? static int n;
??? static boolean flag;
?static boolean[][] Platzierung;
?static boolean[] a;
?static boolean[] b;
?static boolean[] c;
?
?public static void main(String[] args){
??write("Wie viele Damen?");
??n=read();
???? flag=false;
??Platzierung=new boolean[n][n];
??a=new boolean[n];
??b=new boolean[2*n];
??c=new boolean[2*n];
??re(0);
?}
?
?public static void re(int i){
??if(flag)
???return;
??for(int iSpalte=0;iSpalte<n;iSpalte++){
???if(a[iSpalte]==false && b[i-iSpalte+n]==false && c[i+iSpalte]==false){
????Platzierung[i][iSpalte]=true;
????a[iSpalte]=true;
????b[i-iSpalte+n]=true;
????c[i+iSpalte]=true;
????if(i==n-1){
?????paintField(Platzierung);
?????flag=true;
?????return;
????}
????else{
?????re(i+1);
????}
???Platzierung[i][iSpalte]=false;
???a[iSpalte]=false;
???b[i-iSpalte+n]=false;
???c[i+iSpalte]=false;
???}
??}
?}
}


附上ChessMiniJava源代碼：
import java.awt.GridLayout;
import javax.swing.JPanel;
import javax.swing.JFrame;

import java.awt.Color;
import java.awt.Font;
import java.awt.Point;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GradientPaint;
import java.awt.RenderingHints;

public class ChessMiniJava extends MiniJava{
??? private static class Field extends JPanel {
??????? boolean black,queen; Point p;
??????? public Field(boolean black,boolean queen){
??????????? this.black=black;
??????????? this.queen=queen;
??????????? p = getLocation();
??????? }
?public void paint(Graphics g) {
??super.paint(g);
??if (black) g.setColor(Color.BLACK);
??????????????? else g.setColor(Color.WHITE);
??????????????? g.fillRect(p.getLocation().x,p.getLocation().y,getWidth()*2,getHeight());
??????????????? g.setColor(Color.RED);

??????????????? GradientPaint gradient = new GradientPaint(0, 0, Color.YELLOW, getWidth(), 0, Color.RED);
??????????????? ((Graphics2D)g).setPaint(gradient);
??????????????? ((Graphics2D)g).setRenderingHint(RenderingHints.KEY_ANTIALIASING,
??????????????????????? RenderingHints.VALUE_ANTIALIAS_ON);
??????????????? if (queen) {
??????????????????? g.fillOval((int)(getWidth()*.1),(int)(getHeight()*.7),(int)(getWidth()*.8),(int)(getHeight()*.2));
??????????????????? int[] x = {(int)(getWidth()*.1), (int)(getWidth()*.9), (int)(getWidth()*.9), (int)(getWidth()*.7), (int)(getWidth()*.5), (int)(getWidth()*.3), (int)(getWidth()*.1)};
??????????????????? int[] y = {(int)(getHeight()*.8),(int)(getHeight()*.8),(int)(getHeight()*.2),(int)(getHeight()*.6),(int)(getHeight()*.2),(int)(getHeight()*.6),(int)(getHeight()*.2)};
??????????????????? g.fillPolygon(x,y,7);
??????????????? }
?}
??? }
??? public static void paintField(boolean[][] field){
??????? JFrame myFrame = new JFrame("Spielfeld");
??????? JPanel pan = new JPanel();
??????? java.util.Set<Integer> s1 = new java.util.HashSet<Integer>(),s2=new java.util.HashSet<Integer>(),s3 = new java.util.HashSet<Integer>(),s4=new java.util.HashSet<Integer>();
??????? pan.setLayout(new GridLayout(field.length,field.length));
??????? for (int x = 0 ; x < field.length; x ++){
??????????? for (int y = 0; y < field[x].length; y++){
??????????????? pan.add(new Field((x+y)%2 ==1,field[x][y]));
??????????????? if (field[x][y]) { s1.add(x);s2.add(y);s3.add(x+y);s4.add(field.length-1-y+x);};
??????????? }
??????? }
??????? boolean sol=(s1.size()==field.length)&&(field.length==s2.size())&&(field.length==s3.size())&&(field.length==s4.size());
??????? if (System.getProperty("SOL","nowshow").equals("show")){
??????????? if (sol) pan.setBorder(javax.swing.BorderFactory.createLineBorder(Color.GREEN,5));
??????????? else pan.setBorder(javax.swing.BorderFactory.createLineBorder(Color.RED,5));
??????? }
??????? myFrame.add(pan);
??????? myFrame.setSize(400,400);
??????? myFrame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
??????? myFrame.setVisible(true);
??? }
}