Eight
Time Limit: 10000/5000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 8747 Accepted Submission(s): 2387
Special Judge
Problem 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, 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
Source
South Central USA 1998 (Sepcial Judge Module By JGShining)
Recommend
JGShining
思路：
用map存取走過的狀態 總共有9！個狀態
然後用123456780 倒推所有能走到終態的狀態
注意
int dir[4][2]={{-1,0},{1,0},{0,-1},{0,1}};
char fx[] = {'d', 'u', 'r', 'l'};
-1 0對應的方向是down
x減小 x是指橫 那麼應該是向上 應該是up
但是由於是倒推 輸出也要逆序輸出
因為要從終態123456780推出其它狀態 所以輸出要逆序輸出 上就是下 下就是上 左就是右 右就是左
#include<stdio.h>
#include<string>
#include<queue>
#include<map>
using namespace std;
struct haha
{
int pos;
string path;
string str;
haha()
{
pos=0;
}
}q,temp;
int dir[4][2]={1,0,-1,0,0,1,0,-1},pos;
string begin;
char fx[4]={'u','d','l','r'};
map<string,struct haha>mp;
void BFS()
{
int i;
queue<struct haha>que;
q.path="";
q.pos=pos;
q.str=begin;
string mid;
mp[begin].pos=1;
que.push(q);
while(!que.empty())
{
temp=que.front();
que.pop();
for(i=0;i<4;i++)
{
int x=temp.pos/3+dir[i][0];
int y=temp.pos%3+dir[i][1];
if(x<0||x>2||y<0||y>2) continue;
mid=temp.str;
pos=temp.pos;//重
if(i==0)
{
mid[pos+3]=temp.str[pos];
mid[pos]=temp.str[pos+3];
q.pos=pos+3;
}
else if(i==1)
{
mid[pos-3]=temp.str[pos];
mid[pos]=temp.str[pos-3];
q.pos =pos-3;//
}
else if(i==2)
{
mid[pos+1]=temp.str[pos];
mid[pos]=temp.str[pos+1];
q.pos =pos+1;
}
else
{
mid[pos-1]=temp.str[pos];
mid[pos]=temp.str[pos-1];
q.pos =pos-1;
}
if(mp[mid].pos==0)
{
q.path=temp.path;
q.path+=fx[i];
q.str=mid;
mp[mid].path=q.path;
mp[mid].pos=1;
que.push(q);
}
}
}
}
int main()
{
int i ,cnt=0;
char s[2];
begin="12345678x";
pos=8;
BFS();
begin="";
while(scanf("%s",s)!=EOF)
{
cnt++;
begin+=s[0];
if(cnt==9)
{
if(mp[begin].pos==0)
printf("unsolvable\n");
else
{
for(i=mp[begin].path.size()-1;i>=0;i--)
printf("%c",mp[begin].path[i]);
printf("\n");
}
begin="";cnt=0;
}
}
return 0;
