Consider the following solitaire game. You are given an m x m board where each one of the m? positions may be empty or occupied by either a red stone or a blue stone. Initially, some configuration of stones is placed on the board. Then, for each column you must remove either all of the red stones in that column or all of the blue stones in that column. (If a column already has only red stones or only blue stones in it then you do not have to remove any further stones from that column.) The objective is to leave at least one stone in each row. Finding a solution that achieves this objective may or may not be possible depending upon the initial configuration.
Let SOLITAIRE = {(G)|G is a game configuration with a solution}. Prove that SOLITAIRE is NP-
complete.