Decompose the board at narrow aisles

[bernardosulzbach]

Or corridors, I don't know how to call these things.

D D D   D D
D D D C D D D
D D D     D

At the C above, we can split the board B into two smaller boards (B_L and B_R).

D D D
D D D C
D D D

  D D
C D D D
    D

In order to account for all possible solutions, we need to consider clicking C and not clicking C. Also, if C is up, then it may be lowered by the left or the right, but not by both sides. If it is down, it must not be raised. When solving the split boards, C must not be clicked, as clicking it was considered during the split.