Example #1
0
        /// <summary>
        /// The constructor calculates the score if this is a leaf node. Otherwise it builds the rest
        /// of the branch.
        /// </summary>
        /// <param name="game">The game state at this point in the path.</param>
        /// <param name="move">The move taken to get to this game state.</param>
        public MinMaxNode(Game game, Tuple <int, int> move = null)
        {
            this.Move  = move;
            this._game = game;

            // If the game is over, set the scores relative to the X side. When evaluating for O later on,
            // we will just negate the scores as needed.
            if (this._game.IsXWin)
            {
                this._xScore = 1.0;
            }
            else if (this._game.IsOWin)
            {
                this._xScore = -1.0;
            }
            else if (this._game.IsTie)
            {
                this._xScore = 0.0;
            }
            else
            {
                // If we got here, it's because the game is not over. Walk the board and try each of the paths.
                this._children = new List <MinMaxNode>();

                for (int row = 0; row < 3; row++)
                {
                    for (int column = 0; column < 3; column++)
                    {
                        if (this._game.Board.IsEmptyAt(row, column))
                        {
                            // If we can move here, then copy the game, simulate the move, and add the node to the children.
                            Game copy = this._game.Copy();
                            copy.Mark(row, column);

                            // NOTE: Due to the nature of Tic-Tac-Toe, we know that all boards of the same configuration are
                            // identical. To optimize the performance, this step caches each board state by its serialized string
                            // and just reuses identical boards instead of creating new ones and iterating their paths redundantly.
                            if (MinMaxNode._useCache && MinMaxNode._nodeCache.ContainsKey(copy.Board.Serialize()))
                            {
                                this._children.Add(MinMaxNode._nodeCache[copy.Board.Serialize()]);
                            }
                            else
                            {
                                MinMaxNode node = new MinMaxNode(copy, Tuple.Create(row, column));
                                this._children.Add(node);

                                if (MinMaxNode._useCache)
                                {
                                    MinMaxNode._nodeCache.Add(copy.Board.Serialize(), node);
                                }
                            }
                        }
                    }
                }
            }
        }
Example #2
0
        public Tuple <int, int> GetMove(Game game)
        {
            MinMaxNode minMax = new MinMaxNode(game);

            return(minMax.GetMove(game.IsXTurn));
        }