Join the islands with bridges running straight up, down, left or right.
The number on an island says exactly how many bridge ends it must have.
Two islands may be joined by one bridge or two, never more. Bridges
must not cross each other, and must not pass over an island.
You are done when every island can be reached from every other one.
Tap between two islands to cycle one bridge → two → none.
Press Z to undo.
An island turns red when it already has more bridges
than its number allows, or when it can no longer reach its number. Crossed bridges turn red too.
Nothing stops you making these moves — the colour is just there to catch your eye.
There is a paperback of these puzzles, built by the same generator. Every puzzle in it is checked by computer to have exactly one solution.
See the book
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Every puzzle is generated automatically, and only those a dedicated solver has
proved to have exactly one solution are published here.