Minimax.Connect4/MinMaxABFourInARowBoard.cs

using FourInARow;

namespace MinMaxAB;

public class MinMaxABFourInARowBoard
{
    protected int EvaluateScoreDiff((int player, int computer) scores)
    {
        //Console.WriteLine($"V: {scores.computer} {scores.player}");

        if (scores.player == 0 && scores.computer == 0) return 0;

        if (scores.computer > 0)
        {
            return scores.computer switch
            {
                1 => 1,
                2 => 10,
                3 => 100,
                _ => 0
            };
        }

        if (scores.player > 0)
        {
            return scores.player switch
            {
                1 => -1,
                2 => -10,
                3 => -100,
                _ => 0
            }; ;
        }

        return 0;
    }

    // public int CountSequences(GameBoard board, Player player)
    // {
    //     int score = 0;
    //     int hscore = 0;
    //     int vscore = 0;
    //     int dscore = 0;
    //     int rscore = 0;

    //     for (int col = 0; col < board.dimensions.Columns; col++)
    //     {
    //         for (int row = 0; row < board.dimensions.Rows; row++)
    //         {
    //             if (row < board.dimensions.Columns - 4)
    //             {
    //                 int computer = 0;
    //                 int p = 0;
    //                 int c2 = 0;
    //                 int p2 = 0;

    //                 for (int k = 0; k < 4; k++)
    //                 {
    //                     if (board.cells[col, row + k] == player) computer++;
    //                     else if (board.cells[col, row + k] != Player.None) p++;

    //                     if (col < board.dimensions.Rows - 4)
    //                     {
    //                         if (board.cells[col + k, row + k] == player) c2++;
    //                         else if (board.cells[col + k, row + k] != Player.None) p2++;
    //                     }
    //                 }

    //                 hscore += EvaluateScoreDiff((p, computer));
    //                 dscore += EvaluateScoreDiff((p2, c2));
    //             }

    //             if (col < board.dimensions.Rows - 4)
    //             {
    //                 int computer = 0;
    //                 int p = 0;

    //                 for (int k = 0; k < 4; k++)
    //                 {
    //                     if (board.cells[col + k, row] == player) computer++;
    //                     else if (board.cells[col + k, row] != Player.None) p++;
    //                 }

    //                 vscore += EvaluateScoreDiff((p, computer));
    //             }

    //             if (col >= 3 && row < board.dimensions.Columns - 4)
    //             {
    //                 int computer = 0;
    //                 int p = 0;

    //                 for (int k = 0; k < 4; k++)
    //                 {
    //                     if (board.cells[col - k, row + k] == player) computer++;
    //                     else if (board.cells[col - k, row + k] != Player.None) p++;
    //                 }

    //                 rscore += EvaluateScoreDiff((p, computer));
    //             }
    //         }
    //     }
    //     return score;
    // }

    public int CountSequences(GameBoard board, Player player)
    {
        int score = 0;

        // Direction vectors for all 4 directions:
        // Horizontal, Vertical, Diagonal, Reverse Diagonal
        int[,] directions = new int[,] {
        { 0, 1 },  // Horizontal: right
        { 1, 0 },  // Vertical: down
        { 1, 1 },  // Diagonal: down-right
        { -1, 1 }  // Reverse Diagonal: up-right
    };

        for (int row = 0; row < board.dimensions.Rows; row++)
        {
            for (int col = 0; col < board.dimensions.Columns; col++)
            {
                // Check all 4 directions from current position
                for (int dir = 0; dir < 4; dir++)
                {
                    int rowDir = directions[dir, 0];
                    int colDir = directions[dir, 1];

                    // Check if we can fit a sequence of 4 in this direction
                    int endRow = row + (3 * rowDir);
                    int endCol = col + (3 * colDir);

                    if (endRow >= 0 && endRow < board.dimensions.Rows &&
                        endCol >= 0 && endCol < board.dimensions.Columns)
                    {
                        int aiCount = 0;
                        int humanCount = 0;

                        // Check the sequence of 4 cells in current direction
                        for (int k = 0; k < 4; k++)
                        {
                            int currentRow = row + (k * rowDir);
                            int currentCol = col + (k * colDir);

                            if (board.cells[currentCol, currentRow] == player)
                                aiCount++;
                            else if (board.cells[currentCol, currentRow] != Player.None)
                                humanCount++;
                        }

                        // Score the sequence
                        score += EvaluateScoreDiff((humanCount, aiCount));
                    }
                }
            }
        }

        return score;
    }

    private int EvaluateMinMax(GameBoard board, Player player, int depth, bool maxPlayer = false, int alpha = int.MinValue, int beta = int.MaxValue)
    {
        var currentWinner = board.GetWinner();

        if (currentWinner == player) return (depth + 1) * 100_000;
        if (currentWinner! == GameBoard.Opposite(player)) return -(depth + 1) * 100_000;
        if (!board.HasEmptyColumns()) return 0;

        //if (depth == 0) return CountSequences(board, player);
        if (depth == 0)
        {
            return CountSequences(board, player); ;
        }

        int best = maxPlayer ? int.MinValue : int.MaxValue;

        for (int i = 0; i < board.dimensions.Columns; i++)
        {
            if (!board.PlaceCoin(maxPlayer ? player : GameBoard.Opposite(player), i)) continue;

            int x = EvaluateMinMax(board, player, depth - 1, !maxPlayer, alpha, beta);
            best = maxPlayer ? Math.Max(best, x) : Math.Min(best, x);
            board.RemoveFromTop(i);

            if (maxPlayer) alpha = Math.Max(alpha, best);
            else beta = Math.Min(beta, best);

            if (beta <= alpha) i++;
        }

        return best;
    }

    public int GetBestMove(GameBoard board, Player player, int depth)
    {
        List<(int Column, int Score)> moves = [];
        // Parallel.For(0, board.dimensions.Columns, new ParallelOptions() { MaxDegreeOfParallelism = 1 }, i =>
        Parallel.For(0, board.dimensions.Columns, i =>
        {
            var newBoard = (board.Clone() as GameBoard)!;
            if (!newBoard.PlaceCoin(player, i)) return;
            moves.Add((i, EvaluateMinMax(newBoard, player, depth)));
        });
        // for (int i = 0; i < board.dimensions.Columns; i++)
        // {
        //     Console.Write($"\rAI Thinking {(float)i / board.dimensions.Columns:p0}...");
        //     if (!PlaceCoin(player, i)) continue;
        //     moves.Add((i, EvaluateMinMax(player, depth, maxPlayer, alpha, beta)));
        //     RemoveFromTop(i);
        // }

        int maxScore = moves.Max(move => move.Score);
        var bestMoves = moves.Where(move => move.Score == maxScore).OrderBy(move => Math.Abs(move.Column - board.dimensions.Columns / 2)).ToArray();
        // Console.WriteLine(string.Join(" | ", moves.OrderBy(m => m.Column).Select(m => $"{m.Column}:{m.Score}")));
        return bestMoves.ChooseRandom().Column;
    }
}