static GameBoard CalculateMaxMove(GameBoard parent)
{
/* Alpha values are stored in the max nodes
* Alpha value = max(children's Beta Values of min nodes)
* Because we want to minimize opponent moves *
*/
if (parent.GetChildren().Count <= 0)
{
CalculateMoves(parent);
}
GameBoard best_child = null;
if (parent.GetChildren().Count > 0)
{
best_child = parent.GetChildren().ElementAt(0); //best is first child
foreach (GameBoard child in parent.GetChildren())
{
if (CalculateMoves(child) >= parent.GetAlphaBetaValue()) //get max
{
best_child = child; //new best child
parent.SetAlphaBetaValue(best_child.GetAlphaBetaValue());
}
}
return best_child;
}
return null;
}
static GameBoard CalculateMinMove(GameBoard parent)
{
/* Beta values are stored in the min nodes
* Beta value = min(alpha Values of max nodes)
* Because we want to maximize our moves
*
*/
if (parent.GetChildren().Count <= 0)
{
CalculateMoves(parent);
}
GameBoard worst_child = null;
if (parent.GetChildren().Count > 0)
{
worst_child = parent.GetChildren().ElementAt(0);
foreach (GameBoard child in parent.GetChildren())
{
if (CalculateMoves(child) <= parent.GetAlphaBetaValue())
{
worst_child = child;
parent.SetAlphaBetaValue(worst_child.GetAlphaBetaValue());
}
}
return worst_child;
}
return null;
}
static int CalculateAlphaBeta(GameBoard parent, int depth, int alpha, int beta, GameBoard.MinMax player)
{
int moves = 0;
if (parent.GetChildren().Count == 0) //if there are no children for this node
{
moves = CalculateMoves(parent);
}
else
{
moves = parent.GetChildren().Count;
}
if (moves == 0 || depth == 0) //terminal node
{
return parent.GetAlphaBetaValue(); //return non null value
}
if (player == GameBoard.MinMax.Max) //max player
{
foreach (GameBoard child in parent.GetChildren())
{
//children are min nodes
alpha = Math.Max(alpha, CalculateAlphaBeta(child, depth-1, alpha, beta, child.GetNodeType()));
child.SetAlphaBetaValue(alpha);
if(beta <= alpha)
{
parent.GetChildren().Remove(child);
break;
}
}
return alpha;
}
else //min player
{
foreach (GameBoard child in parent.GetChildren())
{
//children are max nodes
beta = Math.Min(beta, CalculateAlphaBeta(child, depth-1, alpha, beta, child.GetNodeType()));
child.SetAlphaBetaValue(beta);
if (beta <= alpha)
{
parent.GetChildren().Remove(child);
break;
}
}
return beta;
}
}