407879: GYM102916 C Cyclically Shifted Maze

Let's call a maze a rectangular field of cells, where cells can either be empty or contain a wall, and one can move from an empty cell to its empty neighbour cells in four directions.

Let's call a maze connected if it's possible to reach any its empty cell from any other empty cell by moving in four directions.

There was a connected maze of size $$$n \times m$$$. It was cyclically shifted some rows down and some columns right, but nobody knows the exact shifts. Find all possible shifts.

The first line contains two integers $$$n$$$ and $$$m$$$ ($$$1 \le n, m \le 200$$$) — the sizes of the maze.

Each of the next $$$n$$$ lines contains $$$m$$$ characters "." or "#" — empty cells and walls, correspondingly.

There is at least one empty cell in the maze.

In the first line output a single integer $$$k$$$ ($$$0 \le k \le n \cdot m$$$) — the number of possible shifts.

In each of the next $$$k$$$ lines output two integers $$$r_i$$$ and $$$c_i$$$ ($$$0 \le r_i < n, 0 \le c_i < m$$$) — the number of rows the original maze was shifted down and the number of columns it was shifted right. Pairs ($$$r_i$$$, $$$c_i$$$) should be output in lexicographical order. Original maze must be connected for each of these cases.

5 6
..####
.###..
...#.#
##...#
.###..

9
0 2
0 3
0 4
1 2
1 3
1 4
4 2
4 3
4 4

8 10
##########
..........
#.####..##
..###..##.
#....##...
######..##
....###...
....###...

2
0 5
1 5