alpha-beta剪枝搜索

// basic Alpha-Beta search;

　move bestmove;






int alphabeta(int depth, int alpha, int beta, bool isMyTurn) ...{






　if (gameOver || depth == 0) ...{


　　return evaluation();


　}




generateLegalMoves();




// you may change the search order to make the search faster






　for (each move m) ...{


　　do move m;


　　score = -alphabeta(depth - 1, -beta, -alpha, ! isMyTurn );




　　if (score > alpha) ...{




alpha = score;




if(at the Level 1) 　




　　bestmove = m;


　　}


　　undo move-m;




　　if (alpha >= beta) ...{


　　　break;


　　}


　}


　return alpha;


}

Initial call : alphabeta(depth, - infinite, infinite, isMyTurn);

不理解上面的代码的话，看看下面的极小极大搜索

极小极大搜索


//极大搜索




int Max(int depth)




...{


　int best = -INFINITY;


　if (depth == 0)




...{


　　return evaluation();


　}


　generateLegalMoves();




　for (each move m) ...{




...{


　　do move m;


　　val = Min(depth - 1); // call the Min search


undo move m;


　　if (val > best)




...{


　　　best = val;


　　}


　}


　return best;


}


　


int Min(int depth) // Min search




...{


　int best = INFINITY;


　if (depth <= 0)




...{


　　return evaluation();


　}


　GenerateLegalMoves();




　for (each move m) ...{


　　do move m;


　　val = Max(depth - 1); // call the Max search


undo move m;


　　if (val < best)




...{


　　　best = val;


　　}


　}


　return best;


}

负极大搜索

极小极大搜索可以统一用负极大搜索代替


int NegaMax(int depth)




...{


　int best = -INFINITY;


　if (depth == 0)




...{


　　return evaluation();


　}


　GenerateLegalMoves();




for (each move m) ...{


　　do move m;


　　val = - NegaMax(depth - 1);


　　undo move m;


　　if (val > best)




...{


　　　best = val;


　　}


　}


　return best;


}