private GameTreeNode MinMax(GameState currentState, int depth, double alpha, double beta, bool maximizingPlayer)
{
visitedNodes++;
GameTreeNode bestMove = null;
if (depth == 0 || currentState.WinningPlayer != PlayerNumber.None)
{
double evaluation = heuristic.Evaluate(currentState);
bestMove = new GameTreeNode(currentState, evaluation);
}
else if (maximizingPlayer)
{
double maxEval = double.NegativeInfinity;
List <GameState> nextStates = currentState.GetAllPossibleNextStates(PlayerNumber.FirstPlayer);
foreach (var nextState in nextStates)
{
GameTreeNode bestChild = MinMax(nextState, depth - 1, alpha, beta, false);
if (bestChild == null)
{
currentState.GetAllPossibleNextStates(PlayerNumber.FirstPlayer);
}
if (maxEval < bestChild.Evaluation)
{
bestMove = new GameTreeNode(nextState, bestChild.Evaluation);
maxEval = bestChild.Evaluation;
}
alpha = Math.Max(alpha, bestChild.Evaluation);
if (beta <= alpha)
{
break;
}
}
}
else
{
double minEval = double.PositiveInfinity;
List <GameState> nextStates = currentState.GetAllPossibleNextStates(PlayerNumber.SecondPlayer);
foreach (var nextState in nextStates)
{
GameTreeNode bestChild = MinMax(nextState, depth - 1, alpha, beta, true);
if (bestChild == null)
{
currentState.GetAllPossibleNextStates(PlayerNumber.SecondPlayer);
}
if (minEval > bestChild.Evaluation)
{
bestMove = new GameTreeNode(nextState, bestChild.Evaluation);
minEval = bestChild.Evaluation;
}
beta = Math.Min(beta, bestChild.Evaluation);
if (beta <= alpha)
{
break;
}
}
}
return(bestMove);
}
public override void MakeMove()
{
GameTreeNode bestPossibleMove = null;
GameState currentState = game.GameState;
if (playerNumber == PlayerNumber.FirstPlayer)
{
bestPossibleMove = MinMax(currentState, searchDepth, Double.NegativeInfinity, Double.PositiveInfinity, true);
}
else
{
bestPossibleMove = MinMax(currentState, searchDepth, Double.NegativeInfinity, Double.PositiveInfinity, false);
}
game.MakeMove(bestPossibleMove.GameState);
}