Colour all squares either blue or black, so as to meet the following conditions:
No two black squares are orthogonally adjacent.
No group of blue squares is separated from the rest of the grid by black squares.
Each numbered cell can see precisely that many blue squares in total by looking in all four orthogonal directions, counting itself. (Black squares block the view. For example, a 2 clue must be adjacent to three black squares or grid edges, and in the fourth direction there must be one blue square and then a black one beyond it.)
If a cell has a red border, it means it has broken one of the above rules
Left-click to mark a square blue, right-click to mark it black, middle click to clear it.
On mobile, tapping a cell multiple times will toggle its colour