Suppose you've been asked to verify a museum's security is up to standard.

You're given a floor plan with the positions of all guards and walls:

4 6
0 0 g
0 1 w
1 1 g
2 2 w
2 3 g

The first line describes the dimensions of the museum, which is a m x n
rectangle (in this case, 4 x 6). m and n are always greater than 0.

Subsequent lines correspond to positions of guards (designated as "g") and
walls (designated as "w"). For example, "0 0 g" designates there is a
guard at (0, 0).

Guards do not move, but can guard any line of rooms that are:

directly to the north, east, south, or west of them
unobstructed (i.e., there is no wall in between them)

For example, the guard at (0, 0) can only guard (1, 0), (2, 0), and (3, 0).

Whereas the guard at (2, 3) can guard (0, 3), (1, 3), (2, 4), (2, 5), and (3, 3).

The above museum looks something like:

0 	1 	2 	3 	4 	5

0 g w -
1 - g - - - -
2 - - w g - -
3 - - -

Guarded rooms have been marked with a "-".

Given a museum, please print your solution in the following format:

false
0 2
0 4
0 5
3 2
3 4
3 5

The first line should be "false" if the museum has unguarded rooms, and "true"
if the museum has no unguarded rooms.

If "false", subsequent lines should be coordinates of unguarded rooms.

Unguarded rooms should be ordered in ascending order by (x, y).

Anybody can tell the approach for this problem?