/// <summary>
/// Runs the minimax algoritm with alpha beta pruning
/// </summary>
/// <param name="board">The board.</param>
/// <param name="depth">The depth.</param>
/// <param name="alpha">The alpha.</param>
/// <param name="beta">The beta.</param>
/// <param name="isMax">if set to <c>true</c> [is maximum].</param>
/// <param name="rootPlayer">The root player.</param>
/// <returns>Minimax value for this board state</returns>
private static int Minimax(CheckerBoard board, int depth, int alpha, int beta, bool isMax, PlayerColor rootPlayer)
{
List <CheckersMove> possibleMoves = board.GetMovesForPlayer();
if (depth == 0 || possibleMoves.Count == 0)
{
return(Score(board, rootPlayer));
}
int value = 0;
if (isMax)
{
value = int.MinValue;
foreach (CheckersMove move in possibleMoves)
{
CheckersMove moveToMake = move;
CheckerBoard boardToMakeMoveOn = board;
do
{
boardToMakeMoveOn = (CheckerBoard)boardToMakeMoveOn.GetMinimaxClone();
boardToMakeMoveOn.MakeMoveOnBoard((CheckersMove)moveToMake.GetMinimaxClone());
moveToMake = moveToMake.NextMove;
}while (moveToMake != null);
int result = Minimax(boardToMakeMoveOn, depth - 1, alpha, beta, false, rootPlayer);
value = Math.Max(result, value);
alpha = Math.Max(alpha, value);
if (alpha >= beta)
{
Logger.Debug("Branch was pruned");
break;
}
}
}
else
{
value = int.MaxValue;
foreach (CheckersMove move in possibleMoves)
{
CheckersMove moveToMake = move;
CheckerBoard boardToMakeMoveOn = board;
do
{
boardToMakeMoveOn = (CheckerBoard)boardToMakeMoveOn.GetMinimaxClone();
boardToMakeMoveOn.MakeMoveOnBoard((CheckersMove)moveToMake.GetMinimaxClone());
moveToMake = moveToMake.NextMove;
}while (moveToMake != null);
int result = Minimax(boardToMakeMoveOn, depth - 1, alpha, beta, true, rootPlayer);
value = Math.Min(result, value);
beta = Math.Min(alpha, value);
if (alpha >= beta)
{
Logger.Debug("Branch was pruned");
break;
}
}
}
return(value);
}
/// <summary>
/// Initial minimax starting method. This method kicks off the algoritm and finds the best move for the current player.
/// If two or more moves have the same value, the best move is choosen randomly from the moves
/// </summary>
/// <param name="board">The board.</param>
/// <returns>Best move for the current player</returns>
public static CheckersMove MinimaxStart(CheckerBoard board)
{
int alpha = int.MinValue;
int beta = int.MaxValue;
thinking = true;
List <CheckersMove> possibleMoves = board.GetMovesForPlayer();
List <int> values = new List <int>();
Logger.Info(string.Format("Max is {0}", board.CurrentPlayerTurn));
if (possibleMoves.IsNullOrEmpty())
{
return(null);
}
foreach (CheckersMove move in possibleMoves)
{
CheckersMove moveToMake = move;
CheckerBoard boardToMakeMoveOn = board;
do
{
Logger.Debug("Board Before");
Logger.Debug(boardToMakeMoveOn.ToString());
boardToMakeMoveOn = (CheckerBoard)boardToMakeMoveOn.GetMinimaxClone();
boardToMakeMoveOn.MakeMoveOnBoard((CheckersMove)moveToMake.GetMinimaxClone());
moveToMake = moveToMake.NextMove;
Logger.Debug("Board After");
Logger.Debug(boardToMakeMoveOn.ToString());
}while (moveToMake != null);
values.Add(Minimax(boardToMakeMoveOn, Settings.AIDepth - 1, alpha, beta, false, board.CurrentPlayerTurn));
}
int maxHeuristics = int.MinValue;
foreach (int value in values)
{
if (value >= maxHeuristics)
{
maxHeuristics = value;
}
}
//filter the list of moves based on max value
List <CheckersMove> bestMoves = new List <CheckersMove>();
for (int i = 0; i < values.Count; i++)
{
if (values[i] == maxHeuristics)
{
bestMoves.Add(possibleMoves[i]);
}
}
counter = 0;
thinking = false;
Logger.Info("Node Values: " + string.Join(",", values.Select(x => x.ToString()).ToArray()));
return(bestMoves[Rng.Next(bestMoves.Count)]);
}
/// <summary>
/// Get all of the horizontal moves. The vertical moves are dependant on the vertical modifier. The direction of the hotizontal move is dependant on the modifier
/// </summary>
/// <param name="currentLocation">The current location.</param>
/// <param name="checkerBoard">The checker board.</param>
/// <param name="oneAdjacentRow">The one adjacent row.</param>
/// <param name="verticalModifier">The vertical modifier.</param>
/// <param name="horizontalModifier">The horizontal modifier.</param>
/// <returns>List of moves</returns>
private List <CheckersMove> ProcessBoardHorizontal(CheckersPoint currentLocation, CheckerBoard checkerBoard, int oneAdjacentRow, int verticalModifier, int horizontalModifier)
{
List <CheckersMove> list = new List <CheckersMove>();
int adjacentCol = currentLocation.Column + (1 * horizontalModifier);
//Check our bounds
if (adjacentCol >= 0 && adjacentCol < 8)
{
CheckerPiece possibleCheckerOnPossiblePoint = checkerBoard.BoardArray[oneAdjacentRow][adjacentCol].CheckersPoint.Checker;
if (possibleCheckerOnPossiblePoint == null || possibleCheckerOnPossiblePoint is NullCheckerPiece)
{
//we can go here
list.Add(new CheckersMove(currentLocation, new CheckersPoint(oneAdjacentRow, adjacentCol)));
}
else
{
//can we jump this guy?
if ((possibleCheckerOnPossiblePoint is IRedPiece && this is IBlackPiece) ||
(possibleCheckerOnPossiblePoint is IBlackPiece && this is IRedPiece))
{
//go another row up and another column to the right
int twoAdjacentRow = oneAdjacentRow + (1 * verticalModifier);
int twoColAdjacent = adjacentCol + (1 * horizontalModifier);
//Check bounds
if (twoColAdjacent >= 0 && twoColAdjacent < 8 && twoAdjacentRow >= 0 && twoAdjacentRow < 8)
{
CheckerPiece possibleCheckerOnPossibleJumpPoint = checkerBoard.BoardArray[twoAdjacentRow][twoColAdjacent].CheckersPoint.Checker;
if (possibleCheckerOnPossibleJumpPoint == null || possibleCheckerOnPossibleJumpPoint is NullCheckerPiece)
{
//we can go here
CheckersMove jumpMove = new CheckersMove(currentLocation, new CheckersPoint(twoAdjacentRow, twoColAdjacent), new CheckersPoint(oneAdjacentRow, adjacentCol));
//This is a jump move
//Get all possible moves for destination point
//For each possible move that is a jump move, make a new move and link it
//make the move on a temp clone of the board and pass that to find any more multimoves
CheckerBoard clonedBoard = (CheckerBoard)checkerBoard.GetMinimaxClone();
clonedBoard.MakeMoveOnBoard((CheckersMove)jumpMove.GetMinimaxClone(), false);
List <CheckersMove> movesAfterJump = this.GetPossibleMoves(jumpMove.DestinationPoint, clonedBoard);
List <CheckersMove> processedList = GetJumpMoves(movesAfterJump);
if (processedList.Count > 0)
{
foreach (CheckersMove move in processedList)
{
CheckersMove clonedMove = (CheckersMove)jumpMove.GetMinimaxClone();
clonedMove.NextMove = move;
list.Add(clonedMove);
}
}
else
{
list.Add(jumpMove);
}
}
}
}
}
}
return(list);
}
