Eight_pku_1077(广搜).java

Eight

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 21718		Accepted: 9611		Special Judge

Description

The 15-puzzle has been around for over 100 years; even if you don't know it by that name, you've seen it. It is constructed with 15 sliding tiles, each with a number from 1 to 15 on it, and all packed into a 4 by 4 frame with one tile missing. Let's call the missing tile 'x'; the object of the puzzle is to arrange the tiles so that they are ordered as:

 1  2  3  4 

 5  6  7  8 

 9 10 11 12 

13 14 15  x

where the only legal operation is to exchange 'x' with one of the tiles with which it shares an edge. As an example, the following sequence of moves solves a slightly scrambled puzzle:

 1  2  3  4    1  2  3  4    1  2  3  4    1  2  3  4 

 5  6  7  8    5  6  7  8    5  6  7  8    5  6  7  8 

 9  x 10 12    9 10  x 12    9 10 11 12    9 10 11 12 

13 14 11 15   13 14 11 15   13 14  x 15   13 14 15  x 

           r->           d->           r->

The letters in the previous row indicate which neighbor of the 'x' tile is swapped with the 'x' tile at each step; legal values are 'r','l','u' and 'd', for right, left, up, and down, respectively.

Not all puzzles can be solved; in 1870, a man named Sam Loyd was famous for distributing an unsolvable version of the puzzle, and

frustrating many people. In fact, all you have to do to make a regular puzzle into an unsolvable one is to swap two tiles (not counting the missing 'x' tile, of course).

In this problem, you will write a program for solving the less well-known 8-puzzle, composed of tiles on a three by three

arrangement.

Input

You will receive a description of a configuration of the 8 puzzle. The description is just a list of the tiles in their initial positions, with the rows listed from top to bottom, and the tiles listed from left to right within a row, where the tiles are represented by numbers 1 to 8, plus 'x'. For example, this puzzle

is described by this list:

 1 2 3 x 4 6 7 5 8

Output

You will print to standard output either the word ``unsolvable'', if the puzzle has no solution, or a string consisting entirely of the letters 'r', 'l', 'u' and 'd' that describes a series of moves that produce a solution. The string should include no spaces and start at the beginning of the line.

Sample Input

 2  3  4  1  5  x  7  6  8

Sample Output

ullddrurdllurdruldr

/*

 * 感言：广搜，题不是太标准，搜索方向顺序不同，结果不同，

 * 不过可以AC，但是有可能会超时

 *

 */

import java.util.ArrayDeque;

import java.util.HashMap;

import java.util.Map;

import java.util.Queue;

import java.util.Scanner;

public class Main{

	static Map<String,Integer> map=new HashMap<String, Integer>();

	static Queue<BFS> q=new ArrayDeque<BFS>();

	static String end="12345678x";

	static char g[]=new char[]{'u','l','d','r'};

	static int d[][]=new int[][]{{-1,0},{0,-1},{1,0},{0,1}};//方向不同结果不同

	public static void main(String[] args) {

		Scanner input=new Scanner(System.in);

		String s[][]=new String[3][3];

		while(input.hasNext()){

			map.clear();

			q.clear();

			BFS text=new BFS();

			for(int i=0;i<3;i++){

				for(int j=0;j<3;j++){

					s[i][j]=input.next();

					if(s[i][j].equals("x")){

						text.setX(i);

						text.setY(j);

					}

				}

			}

			text.setS(s);

			map.put(text.getKey(), 0);

			q.add(text);

			System.out.println(bfs(q));

		}

	}

	private static String bfs(Queue<BFS> q2) {

		while(!q2.isEmpty()){

			BFS text=q2.poll();

			if(end.equals(text.getKey())){

				return text.getPath().toString();

			}

			for(int i=0;i<4;i++){

				int x=text.getX()+d[i][0];

				int y=text.getY()+d[i][1];

				if(x<0||x>=3||y<0||y>=3)

					continue;

				String f[][]=text.copys();

				f[text.getX()][text.getY()]=f[x][y];

				f[x][y]="x";

				BFS st=new BFS();

				st.setX(x);

				st.setY(y);

				st.setS(f);

				st.getPath().append(text.getPath()).append(g[i]);

				String key=st.getKey();

				if(!map.containsKey(key)){

					q2.add(st);

					map.put(key, 0);

				}

			}

		}

		return "unsolvable";

	}

}

class BFS{

	private Integer x,y;

	private String s[][];

	private StringBuilder path=new StringBuilder();

	public String[][] copys(){

		String c[][]=new String[3][3];

		for(int i=0;i<3;i++)

			for(int j=0;j<3;j++){

				c[i][j]=s[i][j];

			}

		return c;

	}

	public String getKey(){

		StringBuilder a=new StringBuilder();

		for(int i=0;i<3;i++){

			for(int j=0;j<3;j++){

				a.append(s[i][j]);

			}

		}

		return a.toString();

	}

	public int getX() {

		return x;

	}

	public void setX(int x) {

		this.x = x;

	}

	public int getY() {

		return y;

	}

	public void setY(int y) {

		this.y = y;

	}

	public String[][] getS() {

		return s;

	}

	public void setS(String[][] s) {

		this.s = s;

	}

	public StringBuilder getPath() {

		return path;

	}

	public void setPath(StringBuilder path) {

		this.path = path;

	}

}

巴特西

Eight_pku_1077(广搜).java

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