We study a popular pencil-and-paper game called morpion solitaire. We present upper and lower bounds for the maximum score attainable for many versions of the game. We also show that, in its most general form, the game is NP-hard and the high score is inapproximable within n1for any > 0 unless P = NP.
Erik D. Demaine, Martin L. Demaine, Arthur Langerm