private double ScoreOpponentState(IGameTree <MOVE> state, int ply, double minimum, double maximum)
{
Debug.Assert(ply >= 0);
Debug.Assert(!state.IsAITurn);
if (ply == 0 || state.ValidMoves.Count == 0)
{
return(state.Score);
}
else
{
var worst = double.PositiveInfinity;
foreach (var validMove in state.ValidMoves)
{
var successorState = state.MakeMove(validMove);
var successorStateScore = ScoreState(successorState, ply - 1, minimum, worst);
if (successorStateScore < worst)
{
worst = successorStateScore;
if (worst <= minimum)
{
return(worst);
}
}
}
return(worst);
}
}
public MOVE GetBestMove(IGameTree <MOVE> state)
{
if (!state.IsAITurn)
{
throw new InvalidOperationException("It is not the AI's turn");
}
else if (state.ValidMoves.Count == 0)
{
throw new InvalidOperationException("No valid moves");
}
else
{
var best = default(MOVE);
var bestScore = double.NegativeInfinity;
foreach (var move in state.ValidMoves)
{
var successorState = state.MakeMove(move);
var successorStateScore = ScoreState(successorState, this._ply - 1);
if (successorStateScore > bestScore)
{
best = move;
bestScore = successorStateScore;
}
}
return(best);
}
}
private double ScoreAIState(IGameTree <MOVE> state, int ply, double minimum, double maximum)
{
Debug.Assert(ply >= 0);
Debug.Assert(state.IsAITurn);
if (state.ValidMoves.Count == 0)
{
return(state.Score);
}
else
{
var best = double.NegativeInfinity;
foreach (var validMove in state.ValidMoves)
{
var successorState = state.MakeMove(validMove);
var successorStateScore = ScoreState(successorState, ply - 1, best, maximum);
if (successorStateScore > best)
{
best = successorStateScore;
if (best >= maximum)
{
return(best);
}
}
}
return(best);
}
}
private double ScoreOpponentState(IGameTree <MOVE> state, int ply)
{
Debug.Assert(ply >= 0);
Debug.Assert(!state.IsAITurn);
if (ply == 0 || state.ValidMoves.Count == 0)
{
return(state.Score);
}
else
{
return(state.ValidMoves.Min(move => ScoreState(state.MakeMove(move), ply - 1)));
}
}