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.