c++实现井子棋（α-β剪枝）

最新推荐文章于 2019-07-28 16:30:32 发布

原创最新推荐文章于 2019-07-28 16:30:32 发布 · 1.4k 阅读

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#α-β剪枝 #minimax算法

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本文介绍了一种基于minimax算法并结合α-β剪枝优化的五子棋AI实现方案，该方案通过递归搜索所有可能的走法来评估最佳行动路径。

在基础模块上增加了minimax算法，并用α-β剪枝优化。

chess.h

public:
    bool canWin(int& bestMove,char c);//minimax

chess.cpp

bool chess::canWin(int& bestMove,char c){//minimax
    for(int i=0;i<number;i++){
        if(isEmpty(i)){
            boardOneLine[i]=c;
            bool win=isWinner(c);
            boardOneLine[i]=blank;
            if(win){
                bestMove=i;
                return true;
            }
        }
    }
    return false;
}

tic_tac_toe.h

static const int blackwin=2;
static const int whitewin=0;
static const int draw=1;

public:
    int getBestMove();//minimax
    void findBlackMove(int& bestMove,int& value,int a,int b);//minimax
    void findWhiteMove(int& bestMove,int& value,int a,int b);//minimax

tic_tac_toe.cpp

void tic_tac_toe::BlackPlace(){
    /*srand(time(NULL));
    while(1){
        int pos=rand()%9;
        if(board.isEmpty(pos)){
            board.placeBlack(pos);
            break;
        }
    }*/
    //minimax
    int bestMove=getBestMove();
    board.placeBlack(bestMove);
}
int tic_tac_toe::getBestMove(){
    int bestMove=0;
    int value=0;
    findBlackMove(bestMove,value,whitewin,blackwin);
    return bestMove;
}
void tic_tac_toe::findBlackMove(int& bestMove,int& value,int a,int b){
    if(board.isFull())
        value=draw;
    else if(board.canWin(bestMove,'X')){
        value=blackwin;
    }
    else{
        value=a;
        for(int i=0;i<number&&value<b;i++){
            if(board.isEmpty(i)){
                board.placeBlack(i);
                int tmp=-1;
                int res=-1;
                findWhiteMove(tmp,res,value,b);
                board.placeBlank(i);
                if(res>value){
                    value=res;
                    bestMove=i;
                }
            }
        }
    }
}
void tic_tac_toe::findWhiteMove(int& bestMove,int& value,int a,int b){
    if(board.isFull())
        value=draw;
    else if(board.canWin(bestMove,'O'))
        value=whitewin;
    else{
        value=b;
        for(int i=0;i<number&&value>a;i++){
            if(board.isEmpty(i)){
                board.placeWhite(i);
                int tmp=-1;
                int res=-1;
                findBlackMove(tmp,res,a,value);
                board.placeBlank(i);
                if(res<value){
                    value=res;
                    bestMove=i;
                }
            }
        }
    }
}

小优化：

void tic_tac_toe::start(){
    Role first=chooseRole();
    if(first==BlackRole){
        //BlackPlace();
        //黑棋第一步随机
        srand(time(NULL));
        int pos=rand()%9;
        if(board.isEmpty(pos))
            board.placeBlack(pos);
    }
    while(1){
        board.printChess();
        if(gameOver())break;
        WhitePlace();
        board.printChess();
        if(gameOver())break;
        BlackPlace();
    }
}

附维基伪代码：

function minimax(node, depth)
    if node is a terminal node or depth = 0
        return the heuristic value of node
    if the adversary is to play at node
        let α := +∞
        foreach child of node
            α := min(α, minimax(child, depth-1))
    else {we are to play at node}
        let α := -∞
        foreach child of node
            α := max(α, minimax(child, depth-1))
    return α

模块化：

tic_tac_toe.h

public:
    int a_b(int& bsm,int player,int a,int b);//a_b

tic_tac_toe.cpp

int tic_tac_toe::getBestMove(){
    int bsm=0;
    a_b(bsm,BlackRole,whitewin,blackwin);
    return bsm;
}
int tic_tac_toe::a_b(int& bsm,int player,int a,int b){
    if(board.isFull())
        return draw;
    else if(player){
        if(board.canWin(bsm,'O'))
            return whitewin;
        else{
            for(int i=0;i<number;i++){
                if(board.isEmpty(i)){
                    board.placeWhite(i);
                    int ans=a_b(bsm,player^1,a,b);
                    board.placeBlank(i);
                    if(ans<b){
                        b=ans;
                        //bsm=i;
                    }
                    if(a>=b)
                        return b;
                }
            }
        }
        return b;
    }
    else {
        if(board.canWin(bsm,'X'))
            return blackwin;
        else{
            for(int i=0;i<number;i++){
                if(board.isEmpty(i)){
                    board.placeBlack(i);
                    int ans=a_b(bsm,player^1,a,b);
                    board.placeBlank(i);
                    if(ans>a){
                        a=ans;
                        bsm=i;
                    }
                    if(a>=b)
                        return a;
                }
            }
        }
        return a;
    }
}