Constraint Programming Models for Solitaire Battleships

The Solitaire Battleships puzzle is described, and a range of constraint programming models are presented. The aim in building these models was to solve difficult instances of the puzzle from CSPLib, without resorting to searching for the solution. These are instances that existing rule-based software for Solitaire Battleships, Fathom It!, cannot solve. The puzzle is quite a challenge to model successfully using CP; a basic model is presented that requires some search even for easy instances. The search effort is much reduced by using regular constraints, at the expense of an increase in run-time. Finally, some of the CSPLib instances have been successfully solved without search, by using shaving. Since Fathom It! already does something very like shaving, this seems a promising route to solving a greater range of instances.