private static MinimaxBestMove FindBestMove(IGameBoard b, long alpha, long beta, int depthLeft)
{
if (depthLeft == 0 || b.IsFinished == true)
{
return(new MinimaxBestMove()
{
Weight = b.BoardWeight,
Move = null
});
}
else
{
MinimaxBestMove move = new MinimaxBestMove();
move.Move = null;
if (b.CurrentPlayer == 1)
{
move.Weight = long.MinValue;
}
else if (b.CurrentPlayer == 2)
{
move.Weight = long.MaxValue;
}
foreach (var m in b.GetPossibleMoves())
{
b.ApplyMove(m);
long w = FindBestMove(b, alpha, beta, depthLeft - 1).Weight;
b.UndoLastMove();
if ((b.CurrentPlayer == 1) && w > alpha)
{
move.Weight = w;
move.Move = m;
alpha = w;
}
else if ((b.CurrentPlayer == 2) && w < beta)
{
move.Weight = w;
move.Move = m;
beta = w;
}
if (!(alpha < beta))
{
return(move);
}
}
return(move);
}
}
//private static MinimaxBestMove FindBestMove(IGameBoard b, int depthLeft, bool maximize) {
private static MinimaxBestMove FindBestMove(IGameBoard b, int depthLeft, bool maximize, int alpha, int beta)
{
// Implement the minimax algorithm.
// Your first attempt will not use alpha-beta pruning. Once that works,
// implement the pruning as discussed in the project notes.
// maximize = player 1
// !maximize = player 2
if (depthLeft == 0 || b.IsFinished)
{
return(new MinimaxBestMove()
{
Weight = b.Weight,
Move = null
});
}
//int bestWeight = maximize ? int.MinValue : int.MaxValue;
IGameMove bestMove = null;
foreach (var m in b.GetPossibleMoves())
{
b.ApplyMove(m);
MinimaxBestMove w = FindBestMove(b, depthLeft - 1, !maximize, alpha, beta);
b.UndoLastMove();
if (maximize && w.Weight > alpha)
{
alpha = w.Weight;
bestMove = m;
}
else if (!maximize && w.Weight < beta)
{
beta = w.Weight;
bestMove = m;
}
if (alpha >= beta)
{
break;
}
}
return(new MinimaxBestMove()
{
Weight = maximize ? alpha : beta,
Move = bestMove
});
}
private static MinimaxBestMove FindBestMove(IGameBoard b, int depthLeft, bool isMaximizing, long alpha, long beta)
{
if (depthLeft == 0 || b.IsFinished)
{
return(new MinimaxBestMove()
{
Weight = b.BoardWeight,
Move = null
});
}
//long bestWeight = isMaximizing ? long.MinValue : long.MaxValue;
//long local_alpha = int.MinValue;
//long local_beta = int.MaxValue;
//alpha = long.MinValue;
//beta = long.MaxValue;
IGameMove bestMove = null;
foreach (IGameMove move in b.GetPossibleMoves())
{
b.ApplyMove(move);
MinimaxBestMove w = FindBestMove(b, depthLeft - 1, !isMaximizing, alpha, beta);
b.UndoLastMove();
if (isMaximizing && w.Weight > alpha)
{
//bestWeight = w.Weight;
bestMove = move;
alpha = w.Weight;
//local_alpha = w.Weight;
}
else if (!isMaximizing && w.Weight < beta)
{
//bestWeight = w.Weight;
bestMove = move;
beta = w.Weight;
//local_beta = w.Weight;
}
if (!(alpha < beta))
{
if (isMaximizing)
{
return(new MinimaxBestMove()
{
Weight = beta,
Move = bestMove
});
}
else
{
return(new MinimaxBestMove()
{
Weight = alpha,
Move = bestMove
});
}
}
}
/*
* return new MinimaxBestMove()
* {
* Weight = bestWeight,
* Move = bestMove
* };
*/
if (isMaximizing)
{
return(new MinimaxBestMove()
{
//Weight = local_alpha,
Weight = alpha,
Move = bestMove
});
}
else
{
return(new MinimaxBestMove()
{
//Weight = local_beta,
Weight = beta,
Move = bestMove
});
}
}
private static MinimaxBestMove FindBestMove(IGameBoard b, int depthLeft, bool maximize, int alpha, int beta)
{
// Implement the minimax algorithm.
// Your first attempt will not use alpha-beta pruning. Once that works,
// implement the pruning as discussed in the project notes.
MinimaxBestMove move = new MinimaxBestMove();
//tree empty
if (depthLeft == 0 || b.IsFinished)
{
move = new MinimaxBestMove();
move.Weight = b.Weight;
move.Move = null;
return(move);
}
//initializaitons
int bestWeight = int.MaxValue;
IGameMove bestMove = null;
if (maximize)
{
bestWeight *= -1;
}
var possMoves = b.GetPossibleMoves();
foreach (var possMove in possMoves)
{
b.ApplyMove(possMove);
//return best move
MinimaxBestMove w = FindBestMove(b, depthLeft - 1, !maximize, alpha, beta);
b.UndoLastMove();
//update alpha
if (maximize && w.Weight > alpha)
{
alpha = w.Weight;
bestWeight = w.Weight;
bestMove = possMove;
//return if alpha not less than beta
if (alpha >= beta)
{
w.Weight = beta;
w.Move = bestMove;
return(w);
}
}
//update beta
else if (!maximize && w.Weight < beta)
{
beta = w.Weight;
bestWeight = w.Weight;
bestMove = possMove;
//return if alpha not less than beta
if (alpha >= beta)
{
w.Weight = alpha;
w.Move = bestMove;
return(w);
}
}
move.Weight = bestWeight;
move.Move = bestMove;
}
return(move);
}
