private int GetBoardValueRecursive(OthelloBoard board, int ply,
int notStuck, int alpha, int beta)
{
//MyTrace(ply, "left="+board.EmptySquares+" alpha="+alpha+" beta="+beta);
/* If the game is over */
if (notStuck == 0 || board.EmptySquares == 0)
{
_finalEvaluations++;
int squareDifference = board.PlayerSquares - board.OpponentSquares;
if (squareDifference > 0)
{
return(squareDifference + 1000);
}
if (squareDifference < 0)
{
return(squareDifference - 1000);
}
// Tie
return(0);
}
#if USE_TRANSPOSITION_TABLE
int moveToTryFirst_X = -1, moveToTryFirst_Y = -1;
bool needToTryFirstMove = false;
int boardHashCode = board.GetHashCode();
int transpositionValue = _transpositionTable.LookupEntry(boardHashCode, ply,
alpha, beta, ref moveToTryFirst_X, ref moveToTryFirst_Y);
if (transpositionValue != AlphaBetaOthelloPlayer.INVALID_MOVE)
{
_transpositionHits++;
return(transpositionValue);
}
if (moveToTryFirst_X >= 0)
{
needToTryFirstMove = true;
}
TranspositionTableElementType elementType = TranspositionTableElementType.Alpha;
OthelloMoveWithData bestMove = null;
#endif
if (ply == 0)
{
_boardEvaluations++;
int val = GetBoardValue(board);
#if USE_TRANSPOSITION_TABLE
_transpositionTable.AddEntry(boardHashCode, 0, val,
TranspositionTableElementType.Exact, -1, -1);
#endif
return(val);
}
int count = 0;
for (int y = 0; y < 8; y++)
{
for (int x = 0; x < 8; x++)
{
OthelloMoveWithData move;
#if USE_TRANSPOSITION_TABLE
if (needToTryFirstMove)
{
move = board.GetMoveInfoIfValid(moveToTryFirst_X, moveToTryFirst_Y);
needToTryFirstMove = false;
// Set x to -1 to make sure that (0,0) gets process next time around
x = -1;
// This could happen if we found an incorrect entry in the table
if (move == null)
{
continue;
}
}
else
{
// Skip this move if we've already tried it
if (x == moveToTryFirst_X && y == moveToTryFirst_Y)
{
continue;
}
move = board.GetMoveInfoIfValid(x, y);
if (move == null)
{
continue;
}
}
#else
move = board.GetMoveInfoIfValid(x, y);
if (move == null)
{
continue;
}
#endif
count++;
/* perform the move */
board.PlayMove(move);
//MyTrace(ply, move.X + "," + move.Y + " alpha="+alpha+" beta="+beta);
int val = (-GetBoardValueRecursive(board, ply - 1, 2, -beta, -alpha));
//MyTrace(ply, move.X + "," + move.Y + " alpha="+alpha+" beta="+beta+" val="+val);
board.UnplayMove(move);
if (val >= beta)
{
#if USE_TRANSPOSITION_TABLE
_transpositionTable.AddEntry(boardHashCode, ply, beta,
TranspositionTableElementType.Beta, move.X, move.Y);
#endif
return(BEST_MOVE);
}
if (val > alpha)
{
alpha = val;
#if USE_TRANSPOSITION_TABLE
elementType = TranspositionTableElementType.Exact;
bestMove = move;
#endif
}
}
}
if (count == 0)
{ /* if no possible move */
board.SwitchPlayer();
int val = -GetBoardValueRecursive(board, ply, notStuck - 1, -beta, -alpha);
board.SwitchPlayer();
return(val);
}
#if USE_TRANSPOSITION_TABLE
if (bestMove != null)
{
_transpositionTable.AddEntry(boardHashCode, ply, alpha, elementType, bestMove.X, bestMove.Y);
}
else
{
_transpositionTable.AddEntry(boardHashCode, ply, alpha, elementType, -1, -1);
}
#endif
return(alpha);
}