2893 -- M × N Puzzle

The Eight Puzzle, among other sliding-tile puzzles, is one of the famous problems in artificial intelligence. Along with chess, tic-tac-toe and backgammon, it has been used to study search algorithms.

The Eight Puzzle can be generalized into an M × N Puzzle where at least one of M and N is odd. The puzzle is constructed with MN − 1 sliding tiles with each a number from 1 to MN − 1 on it packed into a M by N frame with one tile missing. For example, with M = 4 and N = 3, a puzzle may look like:

1	6	2
4	0	3
7	5	9
10	8	11

Let's call missing tile 0. The only legal operation is to exchange 0 and the tile with which it shares an edge. The goal of the puzzle is to find a sequence of legal operations that makes it look like:

1	2	3
4	5	6
7	8	9
10	11	0

The following steps solve the puzzle given above.

START

1	6	2
4	0	3
7	5	9
10	8	11

DOWN
⇒

1	0	2
4	6	3
7	5	9
10	8	11

LEFT
⇒

1	2	0
4	6	3
7	5	9
10	8	11

UP
⇒

1	2	3
4	6	0
7	5	9
10	8	11

…

RIGHT
⇒

1	2	3
4	0	6
7	5	9
10	8	11

UP
⇒

1	2	3
4	5	6
7	0	9
10	8	11

UP
⇒

1	2	3
4	5	6
7	8	9
10	0	11

LEFT
⇒

1	2	3
4	5	6
7	8	9
10	11	0

GOAL

Given an M × N puzzle, you are to determine whether it can be solved.

The input consists of multiple test cases. Each test case starts with a line containing M and N (2 ≤ M, N ≤ 999). This line is followed by M lines containing N numbers each describing an M × N puzzle.

The input ends with a pair of zeroes which should not be processed.