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Colour some squares black, so as to meet the following conditions:
No two black squares are orthogonally adjacent.
No group of white squares is separated from the rest of the grid by
black squares.
Each numbered cell can see precisely that many white squares in
total by looking in all four orthogonal directions, counting itself.
(Black squares block the view. So, for example, a 2 clue must be
adjacent to three black squares or grid edges, and in the fourth
direction there must be one white square and then a black one beyond
it.)
Left-click to colour a square black. Right-click to mark a square
with a dot, if you know it should not be black.