private static KeyValuePair <int, KeyValuePair <int, int> > BestOptionOfSubtree(GameBoard gameBoard)
{
var bestOption = new KeyValuePair <int, KeyValuePair <int, int> >(-2, new KeyValuePair <int, int>());
foreach (var emptySlot in gameBoard.EmptySlots)
{
var tempBoard = (GameBoard)gameBoard.Clone();
tempBoard.Step(emptySlot);
if (tempBoard.IsComplete())
{
return(new KeyValuePair <int, KeyValuePair <int, int> >(tempBoard.Winner, emptySlot));
}
var option = BestOptionOfSubtree(tempBoard).Key;
if (option == gameBoard.Turn)
{
return(new KeyValuePair <int, KeyValuePair <int, int> >(option, emptySlot));
}
if (bestOption.Key == -gameBoard.Turn || bestOption.Key == -2)
{
bestOption = new KeyValuePair <int, KeyValuePair <int, int> >(option, emptySlot);
}
}
return(bestOption);
}
private KeyValuePair <double, KeyValuePair <int, int> > BestOptionOfSubtreeWithCutsAndRestriction(GameBoard gameBoard, int maxDepth, int currentDepth, double parentBest)
{
var currentMultiplier = 1.0 / currentDepth;
var ownBest = -gameBoard.Turn * (double.MaxValue - 1) * currentMultiplier;
var bestSlot = new KeyValuePair <int, int>();
if (gameBoard.EmptySlots.Count != 0)
{
bestSlot = gameBoard.EmptySlots[0];
}
if (gameBoard.IsComplete() || currentDepth == maxDepth)
{
var evaluation = EvaluateGameBoardWithRestriction(gameBoard) * currentMultiplier;
if (gameBoard.Turn * ownBest < gameBoard.Turn * evaluation)
{
ownBest = evaluation;
}
}
else
{
foreach (var emptySlot in gameBoard.EmptySlots)
{
if (!IsSlotInBounds(emptySlot, gameBoard))
{
continue;
}
var tempBoard = (GameBoard)gameBoard.Clone();
tempBoard.Step(emptySlot);
var evaluation = BestOptionOfSubtreeWithCutsAndRestriction(tempBoard, maxDepth, currentDepth + 1, ownBest);
if (gameBoard.Turn * ownBest < gameBoard.Turn * evaluation.Key)
{
ownBest = evaluation.Key;
bestSlot = emptySlot;
}
if (gameBoard.Turn * ownBest >= gameBoard.Turn * parentBest)
{
return(new KeyValuePair <double, KeyValuePair <int, int> >(ownBest, bestSlot));
}
}
}
return(new KeyValuePair <double, KeyValuePair <int, int> >(ownBest, bestSlot));
}