//return move
private int CalculateNextMove(bool firstPlayer, bool turnPlayer, int level, int maxLevel, ref int alpha, ref int beta, Board board)
{
//its just on max level
if (level == maxLevel)
{
return(CalculateCurrentBoard(turnPlayer, board));
}
int localAlpha = alpha;
int localBeta = beta;
int bestResult = firstPlayer == turnPlayer ? int.MinValue : int.MaxValue;
int result = 0;
int bestMove = 0;
for (int i = 0; i < board.NumberOfColumns; i++)
{
Board locBoard = board.Clone();
bool? win = false;
bool put = false;
if (locBoard.PutToken(i))
{
if (locBoard.Result == Result.Draw)
{
win = null;
}
else if (locBoard.Result == Result.None)
{
win = false;
}
else
{
win = true;
}
put = true;
//time to go back in tree
if (win != false || level == maxLevel)
{
if (win == true)
{
result = firstPlayer == turnPlayer ? int.MaxValue : int.MinValue;
}
//draw, so calculate result for turnPlayer
else if (win == null)
{
result = 0;
}
}
//go deeper
else
{
//increase in case of next starting (turn) player
if (firstPlayer == turnPlayer)
{
level++;
}
result = CalculateNextMove(!firstPlayer, turnPlayer, level, maxLevel, ref alpha, ref beta, locBoard);
}
}
if (!put)
{
continue;
}
//there was minimize, so beta is new
if (firstPlayer == turnPlayer)
{
//now we want to maximize
if (result > bestResult)
{
bestResult = result;
if (alpha < bestResult)
{
alpha = bestResult;
}
bestMove = i;
}
if (win == false)
{
level--;
}
if (alpha == int.MaxValue || alpha >= localBeta)
{
break;
}
beta = localBeta;
}
else
{
//minimize
if (result < bestResult)
{
bestResult = result;
if (beta > bestResult)
{
beta = bestResult;
}
bestMove = i;
}
if (beta == int.MinValue || beta <= localAlpha)
{
break;
}
alpha = localAlpha;
}
}
return((level == 0 && firstPlayer == turnPlayer) ? bestMove : bestResult);
}
