Example #1
0
        // Quick sort using transposition table in ascending order
        List <int[, ]> SortByScore(List <int[, ]> list, int color)
        {
            if (list.Count <= 1)
            {
                return(list);
            }

            List <int[, ]> left   = new List <int[, ]>();
            List <int[, ]> center = new List <int[, ]>();
            List <int[, ]> right  = new List <int[, ]>();

            int[,] refBoard = list[0];
            string refBoardHash = BoardToHash(refBoard);
            double refScore;

            if (transpositionTable.ContainsKey(refBoardHash))
            {
                refScore = transpositionTable[refBoardHash].Score;
            }
            else
            {
                OthelloEvaluator tmpEvaluator = new OthelloEvaluator();
                tmpEvaluator.SetBoard(refBoard);
                refScore = tmpEvaluator.Evaluate(selfColor);
                transpositionTable[refBoardHash] = new TranspositionTableEntry(refBoard, currentDepthMax, refScore, "TEMP");
            }
            center.Add(refBoard);

            foreach (int[,] board in list)
            {
                sortAllCount += 1;
                string boardHash = BoardToHash(board);
                double boardScore;
                if (transpositionTable.ContainsKey(boardHash))
                {
                    boardScore = transpositionTable[boardHash].Score;
                }
                else
                {
                    sortEvalCount += 1;
                    OthelloEvaluator tmpEvaluator = new OthelloEvaluator();
                    tmpEvaluator.SetBoard(board);
                    boardScore = tmpEvaluator.Evaluate(selfColor);
                    transpositionTable[boardHash] = new TranspositionTableEntry(board, currentDepthMax, boardScore, "TEMP");
                }

                if (boardScore < refScore)
                {
                    left.Add(board);
                }
                else if (boardScore > refScore)
                {
                    right.Add(board);
                }
                else
                {
                    center.Add(board);
                }
            }

            left  = SortByScore(left, color);
            right = SortByScore(right, color);

            return(left.Concat(center).Concat(right).ToList());
        }
Example #2
0
        // Alpha beta searching with transposition table
        private double AlphaBeta(int[,] board, int color, int depth = 0, double alpha = double.NegativeInfinity, double beta = double.PositiveInfinity)
        {
            nodeCount += 1;

            evaluator.SetBoard(board);

            // Return evaluation value if reaching depth = depthMax or terminal node
            if (depth >= currentDepthMax)
            {
                return(evaluator.Evaluate(selfColor));
            }


            // Return evaluation when game ends
            List <Pos> newOptions    = evaluator.Availables(color);
            List <Pos> oppNewOptions = evaluator.Availables(StoneColor.OppColor(color));

            if (newOptions.Count == 0 && oppNewOptions.Count == 0)
            {
                int selfStones = evaluator.CountStones(selfColor);
                int oppStones  = evaluator.CountStones(StoneColor.OppColor(selfColor));
                if (selfStones > oppStones)
                {
                    return(double.PositiveInfinity);
                }
                else if (selfStones < oppStones)
                {
                    return(double.NegativeInfinity);
                }
                else
                {
                    return(evaluator.Evaluate(selfColor));
                }
            }


            // When only the opponent can put stone, go to next depth
            if (newOptions.Count == 0)
            {
                depth     += 1;
                color      = StoneColor.OppColor(color);
                newOptions = oppNewOptions;
            }


            // Expand board and store the all child boards in children list
            // Associate the child and the action of that time
            List <int[, ]>            children         = new List <int[, ]>();
            Dictionary <int[, ], Pos> actionChildTable = new Dictionary <int[, ], Pos>();

            foreach (Pos action in newOptions)
            {
                Board childBoard = new Board();
                childBoard.SetBoard(board);
                childBoard.UpdateBoard(action, color);
                children.Add(childBoard.GetBoard());
                actionChildTable.Add(childBoard.GetBoard(), action);
            }


            // Sort children in order of the score
            // In descending order when self turn and in ascending order when opponent turn
            st.Start();
            if (depth <= 3)
            {
                children = OrderBoards(children, color);
            }
            st.Stop();


            // Alpha beta searching
            if (color == selfColor)
            {
                // In self turn, search max value of children

                double score = double.NegativeInfinity;

                foreach (int[,] child in children)
                {
                    // Check if the child is stored in transposition table and the node type is EXACT
                    // If it does, set the value for the score
                    // If not, start alpha-beta-searching in next depth and store the score

                    string childHash = BoardToHash(child);

                    if (transpositionTable.ContainsKey(childHash) && transpositionTable[childHash].Depth >= currentDepthMax && transpositionTable[childHash].NodeType == "EXACT")
                    {
                        transpositionCutCount += 1;
                        score = transpositionTable[childHash].Score;
                    }
                    else
                    {
                        score = AlphaBeta(child, StoneColor.OppColor(color), depth + 1, alpha, beta);
                        transpositionTable[childHash] = new TranspositionTableEntry(child, currentDepthMax, score);
                    }


                    if (score > alpha)
                    {
                        alpha = score;

                        // Get best action
                        if (depth == 0)
                        {
                            foreach (KeyValuePair <int[, ], Pos> kvp in actionChildTable)
                            {
                                if (kvp.Key.Cast <int>().SequenceEqual(child.Cast <int>()))
                                {
                                    bestAction = kvp.Value;
                                }
                            }
                        }
                    }

                    // Beta cut
                    if (alpha >= beta)
                    {
                        betaCutCount += 1;
                        break;
                    }
                }
                return(alpha);
            }
            else
            {
                // If the opponent turn, search minimum value of children

                double score = double.PositiveInfinity;

                foreach (int[,] child in children)
                {
                    string childHash = BoardToHash(child);

                    if (transpositionTable.ContainsKey(childHash) && transpositionTable[childHash].Depth >= currentDepthMax && transpositionTable[childHash].NodeType == "EXACT")
                    {
                        transpositionCutCount += 1;
                        score = transpositionTable[childHash].Score;
                    }
                    else
                    {
                        score = AlphaBeta(child, StoneColor.OppColor(color), depth + 1, alpha, beta);
                        transpositionTable[childHash] = new TranspositionTableEntry(child, currentDepthMax, score);
                    }

                    beta = Math.Min(beta, score);

                    // Alpha cut
                    if (beta <= alpha)
                    {
                        alphaCutCount += 1;
                        break;
                    }
                }
                return(beta);
            }
        }