Poj 1077 eight (one-way search)

Eight

Time limit:1000 ms		Memory limit:65536 K
Total submissions:18387		Accepted:8182		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 got 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:

 
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 4 1 2 3 4 4 4
5 6 7 8 5 6 7 8 5 6 6 7 8 5 6 7 8
9x10 12 9 10x12 9 10 11 12 9 10 11 12
13 14 11 15 13 14 11 15 13 14x15 14
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 extends 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 3x4 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 shoshould include no spaces and start at the beginning of the line.

Sample Input

 
2 3 4 1 5x7 6 8
 

Sample output

 
Ullddrurdllurdruldr
 

Source

Write it in various methods in south central USA 1998. Write a new Code :

 /*  Poj 1077 eight one-way search, from the forward start to find the target point Kanto expand as the hash value AC g ++ 8876 K 96 Ms */  # Include <Stdio. h> # Include < String . H> # Include <Iostream> # Include < String > Using   Namespace  STD;  Const   Int Maxn = 362881 ; // 9! = 362880  Struct  Node {  Int S [ 9  ];  Int Pre; //  Record previous Node      Int Dir; //  Record the direction from the previous node to this node  } Que [maxn];  Bool  Hash [maxn];  Int Path [maxn];  Int FAC [] = { 1 , 1 , 2 , 6 , 24 , 120 , 720 , 5040 , 40320 , 362880 }; //  Kangtuo //  0! 1! 2! 3! 4! 5! 6! 7! 8! 9!  Int Cantor ( Int * S ){  Int Sum = 0  ;  For ( Int I = 0 ; I < 9 ; I ++ ){  Int Num =0  ;  For ( Int J = I + 1 ; J < 9 ; J ++ )  If (S [J] < S [I]) num ++ ; Sum + = (Num * FAC [ 9 -I- 1  ]);}  Return SUM ;}  Int Move [ 4 ] [ 2 ] = {{- 1 , 0 },{ 1 , 0 },{ 0 ,- 1 },{ 0 , 1 }}; //  U, D, L, R  Void Output ( Int  Len ){  For ( Int I = len- 1 ; I> = 0 ; I -- ){  If (Path [I] = 0 ) Printf ( "  U  "  );  Else   If (Path [I] =1 ) Printf ( "  D  "  );  Else   If (Path [I] = 2 ) Printf ( "  L  "  );  Else   If (Path [I] = 3 ) Printf ( " R  "  );} Printf (  "  \ N  "  );}  Void  BFS (){  Int Front =- 1 , Rear = 0  ; Que [  0 ]. Pre =- 1  ; Que [ 0 ]. Dir =- 1  ; Memset (hash,  False , Sizeof  (Hash); hash [Cantor (que [  0 ]. S)] = True  ;  If (Cantor (que [ 0 ]. S) = 0 ) {Output ( 0 ); Return  ;} While (Front < Rear) {front ++ ;  Int  TMP;  For (TMP = 0 ; TMP < 9 ; TMP ++ )  If (Que [Front]. s [TMP] = 9  )  Break  ; Int X = tmp/ 3  ;  Int Y = TMP % 3  ;  For ( Int I = 0 ; I < 4 ; I ++ ){  Int Tx = x + move [I] [ 0  ];  Int Ty = Y + move [I] [ 1  ];  If (TX < 0 | TX> 2 | Ty < 0 | Ty> 2 ) Continue  ; Que [rear + 1 ] = Que [Front]; que [rear + 1 ]. Pre = Front; que [rear +1 ]. Dir = I; que [rear + 1 ]. S [TMP] = que [rear + 1 ]. S [TX * 3 + Ty]; que [rear + 1 ]. S [TX * 3 + Ty] = 9  ;  Int Now = Cantor (que [rear + 1  ]. S ); If (Now = 0 ) //  Reach target  {  Int Len = 0  ;  Int T = rear + 1  ;  While (Que [T]. Pre! =- 1  ) {Path [Len ++] =Que [T]. dir; t = Que [T]. Pre;} output (LEN );  Return  ;}  If (! Hash [now]) {rear ++ ; Hash [now] = True  ;}}}}  Int  Main (){  // Freopen ("in.txt", "r", stdin );  //  Freopen ("out.txt", "W", stdout );      Char STR [ 10  ];  While (Scanf ( "  % S  " , & Str )! = EOF ){  If (STR [ 0 ] = '  X ' ) Que [ 0 ]. S [ 0 ] = 9  ;  Else Que [ 0 ]. S [ 0 ] = STR [ 0 ]- '  0  '  ;  For ( Int I =1 ; I < 9 ; I ++ ) {Scanf (  "  % S  " ,& Str );  If (STR [ 0 ] = '  X  ' ) Que [ 0 ]. S [I] = 9  ; Else Que [ 0 ]. S [I] = STR [ 0 ]- '  0  '  ;} BFS ();}  Return   0  ;}