/// <summary>
/// Calculate the heuristic for the state of the board, recursively.
/// </summary>
/// <param name="board">The current state of the board in the search.</param>
/// <param name="depth">The current depth of the search.</param>
/// <param name="nodesVisitedCount">The total number of nodes visited.</param>
/// <param name="move">The best move.</param>
/// <returns>The heuristic for this node in the search.</returns>
private int CalculateMiniMaxHeuristic(Board board, int depth,
ref int nodesVisitedCount, out Move move)
{
// safety-check the board parameter
if (board == null)
{
throw new ArgumentNullException("board");
}
bool myTurn = board.CurrentColor == BoardColor;
BoardColors currentColor = myTurn ? BoardColor :
(BoardColor == BoardColors.White ? BoardColors.Black : BoardColors.White);
int heuristic = myTurn ? Int32.MaxValue * -1 : Int32.MaxValue;
nodesVisitedCount++;
move = new Move(-1, -1);
// cut short the algorithm if it's time to give up
if (nodesVisitedCount >= nodesVisitedLimit)
{
return(0);
}
// at the bottom of the tree, just calculate the value
if (depth <= 0)
{
return(CalculateMiniMaxHeuristic(board));
}
for (int row = 0; row < board.BoardSize; row++)
{
for (int column = 0; column < board.BoardSize; column++)
{
Move newMove = new Move(row, column);
Board newBoard = board.CheckMove(BoardColor, newMove);
if (newBoard != null)
{
Move deeperMove; // we only care about moves in the top level
int newHeuristic = CalculateMiniMaxHeuristic(newBoard,
depth - 1, ref nodesVisitedCount, out deeperMove);
if (nodesVisitedCount >= nodesVisitedLimit)
{
move = newMove;
return(0);
}
if ((myTurn && (newHeuristic > heuristic)) ||
(!myTurn && (newHeuristic < heuristic)))
{
move = newMove;
heuristic = newHeuristic;
}
}
}
}
return(heuristic);
}
