[Home|Training|Problems|Contests|C Language] | [Login|Register] |

Problems Status Rank |
Problem 1012
Eight
Time Limit: 1000ms
Memory Limit: 65536kb 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 xwhere 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 8is 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 |

University of Science and Technology of China

Online Judge for ACM/ICPC

Processed in 1.7ms with 1 query(s).

Online Judge for ACM/ICPC

Processed in 1.7ms with 1 query(s).