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
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.
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 map=new HashMap();
static Queue q=new ArrayDeque();
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 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)){