Two Not Touch: Star Battle

75 boards, from a gentle six-by-six to nine-by-nine with two stars a line. Every one has a single answer, and every one can be reached by reasoning.

Star Battle, also called Two Not Touch or Queens: place stars on the grid so that every row, every column and every shape holds the same number, and no two stars ever touch — not even at a corner.

Every board here has exactly one answer, and every board can be reached by reasoning. That is not a promise in a description: a solver that shares no code with the generator counts the solutions and refuses anything with more than one, and a second solver that does no searching at all has to finish the board from empty before it is allowed into the app. A puzzle you could only crack by trying a placement and undoing it never ships.

75 boards in five sets, from a gentle six-by-six to nine-by-nine with two stars a line.

Tap a square once to mark it empty, twice to place a star. That is the whole of it.

What this app does and does not do:

• No advertising.
• No in-app purchases and no subscription.
• No account and no sign-up.
• Works without a connection. The app itself sends nothing anywhere.
• Collects nothing about you.
• Which boards you have finished is kept on your device.