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Place light bulbs in the grid so as to light up all the blank
squares. A light illuminates its own square and all the squares in
the same row or column unless blocked by walls (black squares).
Lights may not illuminate each other. Each numbered square must be
orthogonally adjacent to exactly the given number of lights.
Click on a square to place or remove a light. Right-click to place a
dot indicating that you think there is no light in that square.