eight（hdu-1043）（待修正）

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, several descriptions of configuration of the 8 puzzle. One 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

1 2 3
x 4 6
7 5 8

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. Do not print a blank line between cases.
Sample Input
2 3 4 1 5 x 7 6 8
Sample Output
ullddrurdllurdruldr
超时：

import java.util.HashSet;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;
import java.util.Stack;

public class A
{   
    static int c;
    static int b[]={-1,1,-3,3};
    static int tar=123456789;
    public static void main(String[] args) 
    {
        Scanner sc=new Scanner(System.in);
        HashSet set=new HashSet<>();
        while(sc.hasNext())
        {
            String s;
            int index=0;
            int org=0;;
            for(int i=0;i<9;i++)
            {
                s=sc.next();
                if(!s.equals("x"))
                {
                    org=org*10+Integer.valueOf(s);
                }
                else
                {
                    org=org*10+9;
                    index=i;
                }
            }
            Queue queue=new LinkedList<>();
            queue.add(new state(org,' ',index,null));
            set.add(org);
            boolean sign=true;
            state ans=null;
            while(!queue.isEmpty()&&sign)
            {
                state t=queue.poll();
                int a[]=getArray(t.s);
                for(int i=0;i<4;i++)
                {
                    if(!check(t.x,i))
                        continue;
                    int p=t.x+b[i];
                    int temp=a[t.x];
                    a[t.x]=a[p];
                    a[p]=temp;
                    int m=getS(a);
                    if(m==tar)
                    {
                        sign=false;
                        ans=new state(m,get(i),p,t);
                        break;
                    }
                    else
                        if(!set.contains(m))
                        {
                            queue.add(new state(m,get(i),p,t));
                            set.add(m);
                        }
                    a[p]=a[t.x];
                    a[t.x]=temp;
                }
            }
            if(sign)
                System.out.println("unsolvable");
            else
            {
                Stackstack=new Stack<>();
                while(ans!=null)
                {
                    stack.add(ans);
                    ans=ans.last;
                }
                stack.pop();
                while(!stack.isEmpty())
                    System.out.print(stack.pop().c);
                System.out.println();
            }
            set.clear();
        }
    }
    static int[] getArray(int s)
    {
        int a[]=new int[9];
        int g=100000000;
        for(int i=0;i<9;i++)
        {
            a[i]=s/g;
            s%=g;
            g/=10;
        }
        return a;
    }
    static int getS(int[] a)
    {
        int s=0;
        for(int i=0;i<9;i++)
        {
            s=s*10+a[i];
        }
        return s;
    }
    static char get(int x)
    {
        switch (x)
        {
        case 0: return 'l';
        case 1: return 'r';
        case 2: return 'u';
        case 3: return 'd';
        }
        return 0;
    }
    static boolean check(int x,int t)
    {
        if(t==0)
        {
            if(x==0||x==3||x==6)
                return false;
        }
        else
            if(t==1)
            {
                if(x==2||x==5||x==8)
                    return false;
            }
            else
                if(t==2)
                {
                    if(x==0||x==1||x==2)
                        return false;
                }
                else if(x==6||x==7||x==8)
                        return false;
        return true;
    }
}
class state
{
    int s;
    char  c;
    state last;
    int x;
    state(int s,char c,int x ,state last)
    {
        this.s=s;
        this.c=c;
        this.last=last;
        this.x=x;
    }
}