Minimax Beta剪枝不起作用，但Minimax单独起作用
Minimax Beta剪枝不起作用，但Minimax单独起作用
提问于 2021-02-09 22:31:35
我的问题是在对Minimax应用Alpha/Beta修剪时。它做了非常奇怪和糟糕的动作。当我使用没有Alpha/Beta的Minimax时，它工作得很好。这两个函数如下所示：
带有Alpha/Beta剪枝的Minimax：
public int minimaxAB(Piece[,] board, int depth, int a, int b, bool maximizingPlayer, bool WhiteToPlay)
{
if (depth == 0)
{
return EvaluatePosition(board, WhiteToPlay);
}
var moves = GenerateMoves(board, WhiteToPlay);
if (maximizingPlayer)
{
int value = int.MinValue;
foreach (var move in moves)
{
int minmaxResult = minimaxAB(move, depth - 1, a, b, false, !WhiteToPlay);
value = Math.Max(value, minmaxResult);
a = Math.Max(a, value);
if (a >= b)
return a;
if (depth == depthB)
{
moveScores.Add(move, minmaxResult);
}
}
return value;
}
else
{
int value = int.MaxValue;
foreach (var move in moves)
{
int minmaxResult = minimaxAB(move, depth - 1, a, b, true, !WhiteToPlay);
value = Math.Min(value, minmaxResult);
b = Math.Min(b, value);
if (b <= a)
return b;
if (depth == depthB)
{
moveScores.Add(move, minmaxResult);
}
}
return value;
}
}没有A/B的Minimax：
public int minimax(Piece[,] board, int depth, bool maximizingPlayer, bool WhiteToPlay)
{
if (depth == 0)
{
int result = EvaluatePosition(board, WhiteToPlay);
return result;
}
var moves = GenerateMoves(board, WhiteToPlay);
if (maximizingPlayer)
{
int value = int.MinValue;
foreach (var move in moves)
{
int minmaxResult = minimax(move, depth - 1, false, !WhiteToPlay);
value = Math.Max(value, minmaxResult);
if (depth == depthB)
{
moveScores.Add(move, minmaxResult);
}
}
return value;
}
else
{
int value = int.MaxValue;
foreach (var move in moves)
{
int minmaxResult = minimax(move, depth - 1, true, !WhiteToPlay);
value = Math.Min(value, minmaxResult);
if (depth == depthB)
{
moveScores.Add(move, minmaxResult);
}
}
return value;
}
}我的求值函数：
public int EvaluatePosition(Piece[,] boardPos, bool ForWhite)
{
int eval_W = 0;
int eval_B = 0;
int eval = 0;
for (int i = 0; i < 8; i++)
{
for (int j = 0; j < 8; j++)
{
if (boardPos[i, j] != Piece.Empty)
{
if (IsPieceWhite(boardPos[i, j]))
{
eval_W += GetPieceWorth(boardPos[i, j]) + DistanceToCenter(i, j);
eval += GetPieceWorth(boardPos[i, j]);
}
else if (IsPieceBlack(boardPos[i, j]))
{
eval_B += GetPieceWorth(boardPos[i, j]) + DistanceToCenter(i, j);
eval -= GetPieceWorth(boardPos[i, j]);
}
}
}
}
if (ForWhite)
return eval_W - eval_B;
else
return eval_B - eval_W;
}我使用的是：minimaxAB(CurrentBoard, depthB, int.MinValue, int.MaxValue, true, whiteToMove);
我知道带有AB的Minimax应该会产生完全相同的结果，但在我的例子中并非如此。我希望有人能发现我做错了什么。
回答 1
Stack Overflow用户
发布于 2021-02-10 23:52:25
我弄明白了，我需要一个白和黑的alpha和beta。这是因为我对白色和黑色移动都调用了minimaxAB函数。
工作方法：
public int minimaxAB(Piece[,] board, int depth, int alpha_White, int beta_White, int alpha_Black, int beta_Black, bool maximizingPlayer, bool WhiteToPlay)
{
if (depth == 0 || !HasKings(board))
{
return EvaluatePosition(board, WhiteToPlay);
}
var moves = GenerateMoves(board, WhiteToPlay);
if (maximizingPlayer)
{
int value = int.MinValue;
foreach (var move in moves)
{
int minmaxResult = minimaxAB(move, depth - 1, alpha_White, beta_White, alpha_Black, beta_Black, false, !WhiteToPlay);
value = Math.Max(value, minmaxResult);
if (WhiteToPlay)
{
alpha_White = Math.Max(alpha_White, value);
if (alpha_White >= beta_White)
return alpha_White;
}
else
{
alpha_Black = Math.Max(alpha_Black, value);
if (alpha_Black >= beta_Black)
return alpha_Black;
}
if (depth == depthB)
{
moveScores.Add(move, minmaxResult);
}
}
return value;
}
else
{
int value = int.MaxValue;
foreach (var move in moves)
{
int minmaxResult = minimaxAB(move, depth - 1, alpha_White, beta_White, alpha_Black, beta_Black, true, !WhiteToPlay);
value = Math.Min(value, minmaxResult);
if (WhiteToPlay)
{
beta_White = Math.Min(beta_White, value);
if (beta_White <= alpha_White)
return beta_White;
}
else
{
beta_Black = Math.Min(beta_Black, value);
if (beta_Black <= alpha_Black)
return beta_Black;
}
if (depth == depthB)
{
moveScores.Add(move, minmaxResult);
}
}
return value;
}
}调用时使用：
minimaxAB(CurrentBoard, depthB, int.MinValue, int.MaxValue, int.MinValue, int.MaxValue, true, whiteToMove);页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/66121002
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