java - Minimax 算法不返回最佳移动

Question

我正在使用带 alpha-beta 剪枝的极小极大算法编写黑白棋引擎。它工作正常，但我发现了以下问题:

当算法发现位置丢失时，它会按预期返回 -INFINITY，但在在这种情况下，我无法追踪“最佳”走法……位置已经丢失，但无论如何它都应该返回有效走法(最好是能存活更长时间的走法，就像优秀的国际象棋引擎一样)。

代码如下:

private float minimax(OthelloBoard board, OthelloMove best, float alpha, float beta, int depth)
{             
    OthelloMove garbage = new OthelloMove();             
    int currentPlayer = board.getCurrentPlayer();

    if (board.checkEnd())
    {                        
        int bd = board.countDiscs(OthelloBoard.BLACK);
        int wd = board.countDiscs(OthelloBoard.WHITE);

        if ((bd > wd) && currentPlayer == OthelloBoard.BLACK)                
            return INFINITY;
        else if ((bd < wd) && currentPlayer == OthelloBoard.BLACK)                           
            return -INFINITY;            
        else if ((bd > wd) && currentPlayer == OthelloBoard.WHITE)                            
            return -INFINITY;            
        else if ((bd < wd) && currentPlayer == OthelloBoard.WHITE)                            
            return INFINITY;            
        else                             
            return 0.0f;            
    }
    //search until the end? (true during end game phase)
    if (!solveTillEnd )
    {
        if (depth == maxDepth)
            return OthelloHeuristics.eval(currentPlayer, board);
    }

    ArrayList<OthelloMove> moves = board.getAllMoves(currentPlayer);             

    for (OthelloMove mv : moves)
    {                        
        board.makeMove(mv);            
        float score = - minimax(board, garbage, -beta,  -alpha, depth + 1);           
        board.undoMove(mv);             

        if(score > alpha)
        {  
            //Set Best move here
            alpha = score;                
            best.setFlipSquares(mv.getFlipSquares());
            best.setIdx(mv.getIdx());        
            best.setPlayer(mv.getPlayer());                              
        }

        if (alpha >= beta)
            break;                

    }                
    return alpha;
}

我这样调用它:

AI ai = new AI(board, maxDepth, solveTillEnd);

//create empty (invalid) move to hold best move
OthelloMove bestMove = new OthelloMove();
ai.bestFound = bestMove;
ai.minimax(board, bestMove, -INFINITY, INFINITY, 0);

//dipatch a Thread
 new Thread(ai).start();
//wait for thread to finish

OthelloMove best = ai.bestFound();

当搜索丢失的位置(例如，假设它在 10 步之后丢失)时，上面的最佳变量等于作为参数传递的空无效移动...为什么？？

感谢您的帮助!

Answer 1

您的问题是您使用 -INFINITY 和 +INFINITY 作为输赢分数。您的赢/输分数应该高于/低于任何其他位置评估分数，但不等于您的无穷大值。这将保证即使在无可救药的情况下也会选择一步棋。