how can we do this? :-/
i could only figure out that ,in your example (1,2,3,4)
for,1 to be filled,2 should be filled .
for 2 to be filled,1 or 3 should be filled.
for 3 to be filled,2 and 4 should be filled.
and for 4 to be filled,3 should be filled.
for corner rooms,the probability that they are filled is 1/nC2
for other rooms,the probabioty that they are filled is 2/nC2 (considering their adjacent rooms)
pls help further in solving and correct me :)