Minimax 工作正常，但 Alpha-beta 剪枝不行

问题描述

我正在尝试使 Alpha-beta 修剪工作，但与我的 Minimax 函数相比，它给了我完全错误的动作。这是我的 Minimax 函数，它现在运行良好。

float Minimax(char[,] _board,int depth,bool isMax) {
    if (depth == 0 || isFull(_board)) {
        EvaluateBoard(_board);
    }

    if (isMax) {
        float bestscore = -Mathf.Infinity;
        float score = -Mathf.Infinity;

        for (int i = 0; i < 7; i++) {
            char[,] board = (char[,]) _board.Clone();
            if (Play(board,i,false)) {
                score = Minimax(board,depth - 1,false);
                bestscore = Mathf.Max(score,bestscore);
            }
        }
        return bestscore;
    } else {
        float bestscore = Mathf.Infinity;
        float score = Mathf.Infinity;

        for (int i = 0; i < 7; i++) {
            char[,true)) {
                score = Minimax(board,true);
                bestscore = Mathf.Min(score,bestscore);
            }
        }
        return bestscore;
    }
}

这是我的 Alphabeta 修剪函数

float ABPruning(char[,float alpha,float beta,bool isMax) {
    if (depth == 0 || isFull(_board)) {
        return EvaluateBoard(_board);
    }
    if (isMax) {
        float bestscore = -Mathf.Infinity;
        
        for (int i = 0; i < 7; i++) {
            char[,false)) {
                bestscore = ABPruning(board,alpha,beta,false);
                alpha = Mathf.Max(alpha,bestscore);
                if (beta<=alpha) {
                    return bestscore;
                }

            }
        }
        return bestscore;
    } else {
        float bestscore = Mathf.Infinity;

        for (int i = 0; i < 7; i++) {
            char[,true)) {
                bestscore = ABPruning(board,true);
                beta = Mathf.Min(beta,bestscore);
                if (beta<=alpha) {
                    break;
                }

            }
        }
        return bestscore;
    }
}

两者都使用相同的评估，不确定这里有什么问题。感谢您的帮助。

解决方法

不清楚您是否正在尝试实施 Fail-hard or Fail-soft methods，但我认为是后者。如果是这样，那么虽然我无法为您测试，但我认为这就是您想要的：

float ABPruning(char[,] _board,int depth,float alpha,float beta,bool isMax) {
    if (depth == 0 || isFull(_board)) {
        return EvaluateBoard(_board);
    }
    if (isMax) {
        float bestScore = -Mathf.Infinity;
        
        for (int i = 0; i < 7; i++) {
            char[,] board = (char[,]) _board.Clone();
            if (Play(board,i,false)) {
                bestScore = Mathf.Max(bestScore,ABPruning(board,depth - 1,alpha,beta,false));
                alpha = Mathf.Max(alpha,bestScore);
                if (bestScore>=beta) {
                    break;
                }
            }
        }
        return bestScore;
    } else {
        float bestScore = Mathf.Infinity;

        for (int i = 0; i < 7; i++) {
            char[,true)) {
                bestScore = Mathf.Min(bestScore,true));
                beta = Mathf.Min(beta,bestScore);
                if (bestScore<=alpha) {
                    break;
                }
            }
        }
        return bestScore;
    }
}