Boats are out at sea, each filling one square, and lighthouses stand guard. Each lighthouse number tells you how many boats are in its row and its column put together.
Boats keep their distance: they never touch each other or a lighthouse, not even diagonally. And every boat sails in sight of at least one lighthouse — in the same row or column.
Start with the 0s and the squares no lighthouse can see; then the counts and the no-touching rule pin down every boat.
Place one-square boats so each lighthouse counts the boats in its row and column; boats never touch and are always in sight of a lighthouse.
The full guide, with a worked example and common mistakes: How to play Lighthouses.
No — a lighthouse counts every boat in its whole row and column.
Yes — every boat here fills exactly one square.
Yes — every puzzle is checked so that logic alone finds every boat.