/*<span style="white-space:pre">	</span>by wbin  2015/12/18

实现n皇后问题的回溯法过程，以java图形界面展示,代码写得略丑，见谅.*/

import java.awt.Color;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.Label;

import javax.swing.JFrame;

public class Main {
	JFrame frame;
	int n=8;			//问题规模
	int waitTime=500;	//时间间隔
	Label mp[][]=new Label[n+1][n+1];
	Thread thread;
	public void create(){
		frame=new JFrame(String.valueOf(n)+"皇后问题");
		frame.setLayout(new GridLayout(n,n));
		Font font=new Font("",Font.BOLD,32);
		for(int i=1;i<=n;i++){
			for(int j=1;j<=n;j++){
				mp[i][j]=new Label();
				if((i+j)%2==0){
					mp[i][j].setBackground(Color.black);
				}
				else{
					mp[i][j].setBackground(Color.white);
				}
				mp[i][j].setFont(font);
				mp[i][j].setForeground(Color.blue);
				frame.add(mp[i][j]); 
			}
		}
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setSize(n*60, n*60); 
		frame.setVisible(true);
		thread=Thread.currentThread();
		
		try {
			dfs(1);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	
	int vis[]=new int[n+1];
	int ans=0;
	public void dfs(int row) throws InterruptedException{
		if(row==n+1){
			ans++;
			System.out.print("第"+ans+"种摆法为：");
			for(int i=1;i<=n;i++){
				System.out.print(vis[i]+",");
			}
			System.out.println();
			for(int i=1;i<=n;i++){
				for(int j=1;j<=n;j++){
					mp[i][j].setForeground(Color.green);
				}
			}
			thread.sleep(3*waitTime);
			for(int i=1;i<=n;i++){
				for(int j=1;j<=n;j++){
					mp[i][j].setForeground(Color.blue);
				}
			}
			return;
		}
		else{
			for(int i=1;i<=n;i++){
				vis[row]=i;
				if(i>1)
					mp[row][i-1].setText("");
				mp[row][i].setText("K");
				boolean state=check(row);
				thread.sleep(waitTime);
				for(int z=1;z<=n;z++){
					for(int j=1;j<=n;j++){
						if((z+j)%2==0){
							mp[z][j].setBackground(Color.black);
						}
						else{
							mp[z][j].setBackground(Color.white);
						}
					}
				}
				if(state){
					dfs(row+1);
				}
				mp[row][i].setText("");
			}
		}
	}
	
	public boolean check(int row){
		boolean flag1=true,flag2=true,flag3=true;
		int row1=1,row2=1,row3=1;
		for(int i=1;i<row;i++){
			if(vis[i]==vis[row]){
				flag1=false;
				row1=i;
			}
			if( (i-row)==(vis[i]-vis[row])){	
				flag2=false;
				row2=i;
			}
			if((i-row)==-(vis[i]-vis[row])){
				flag3=false;
				row3=i;
			}
		}
		if(!flag1){
			for(int i=row;i>=row1;i--)
				mp[i][vis[row]].setBackground(Color.red);
		}
		if(!flag2){
			for(int i=row,j=vis[row];i>=row2;i--,j--){	
				mp[i][j].setBackground(Color.red);
			}
		}
		if(!flag3){
			for(int i=row,j=vis[row];i>=row3;i--,j++){
				mp[i][j].setBackground(Color.red);
			}
		}
		if(!flag1 || !flag2 || !flag3)
			return false;
		return true;
	}
	
	public static void main(String args[]){
		javax.swing.SwingUtilities.invokeLater(new Runnable(){
			@Override
			public void run() {
				// TODO Auto-generated method stub
				(new Main()).create();
			}
		});	
	}
}