α-β剪枝算法的java语言实现（非常实用）

利用α-β剪枝算法，对下图所示的博弈树进行搜索，搜索得到根节点选择的走步，以及没有必要进行评估的节点，并求出给出在何处发生了剪枝，以及剪枝的类型(属于α剪枝还是β剪枝)。

注：□表示MIN节点；○表示MAX节点

 

 

 

public interface Interface{

    public void getStrategy(String InputFile);
    
}

import java.util.*;
import java.io.*;

public class AlphaBeta implements Interface{
    final int MAX_INT=32767; 
    final int MIN_INT=-32768;    
    final int MAX=1;   //极大节点
    final int MIN=0;    //极小节点

    public class Node
    {
        private String name;  
        private int value;                              
        private int leval;//节点判断极大层还是极小层
        private String pFather;
        private ArrayList<String> pChildren;
        
        Node(String name)
        {
            this.name=name;    
            value=-1;
            pFather=new String();
            pChildren=new ArrayList<String>();
        }
        
    }


    private ArrayList<Node> NodeTree;
    private String jianzhi[];   
    private int count;
    
    public void getStrategy(String inputFile){
        NodeTree=new ArrayList<Node>();
        jianzhi=new String[20];
        count=0;
        readTree(inputFile);
        Alph_Beta(NodeTree.get(0).name); 
        System.out.println(count);
        String bestRoute="";
        for(int i=0;i<NodeTree.get(0).pChildren.size();i++)
        {
            if(NodeTree.get(0).value==NodeTree.get(search(NodeTree.get(0).pChildren.get(i))).value)
                {
                    bestRoute=NodeTree.get(0).name+" "+NodeTree.get(0).value+" "+NodeTree.get(search(NodeTree.get(0).pChildren.get(i))).name;
                    break;
                }
                
        }
        System.out.println(bestRoute);
        for(int i=0;i<count;i++)
            {
                System.out.println(jianzhi[i]);
            }
            
    }
    void Alph_Beta(String str) 
    {
        boolean flag=false;
        Node nNode=NodeTree.get(search(str));
        if(nNode.leval==MAX)  
        {
            for(int i=0;i<nNode.pChildren.size();i++) 
            {
                Alph_Beta(nNode.pChildren.get(i));
                if(nNode.value<NodeTree.get(search(nNode.pChildren.get(i))).value)
                {
                    nNode.value=NodeTree.get(search(nNode.pChildren.get(i))).value;
                    if(Beta(str))//是否在极大点出执行Beta剪枝
                    {
                        jianzhi[count]=str+":";
                        for(int j=i+1;j<nNode.pChildren.size();j++)
                        {
                            jianzhi[count]=jianzhi[count]+" "+nNode.pChildren.get(j)+" β剪枝 ";
                            flag=true;
                        }
                        if(flag==true)
                        {    
                            count++;
                        }
                        return;
                    }
                }
            }
        }
        else 
        {
            for(int i=0;i<nNode.pChildren.size();i++)  
            {
                Alph_Beta(nNode.pChildren.get(i));
                if(nNode.value>NodeTree.get(search(nNode.pChildren.get(i))).value)
                {
                    nNode.value=NodeTree.get(search(nNode.pChildren.get(i))).value;
                    if(Alpha(str))
                    {
                        jianzhi[count]=str+":";
                        for(int j=i+1;j<nNode.pChildren.size();j++)
                        {
                            jianzhi[count]=jianzhi[count]+" "+nNode.pChildren.get(j)+"   α剪枝";
                            flag=true;
                        }
                        if(flag==true)
                        {
                            count++;
                        }
                        return;
                    }
                }
            }
        }
    }
    boolean Alpha(String str)
    {
        Node nNode=NodeTree.get(search(str));
        if(nNode.pFather==null) 
        {
            return false;
        }
        int i=search(nNode.pFather);
        while(i>=0)
        {
            if((NodeTree.get(i).value>=nNode.value)&&
                    (NodeTree.get(i).leval==MAX)&&((NodeTree.get(i).value!=MIN_INT)))
                            return true;
            else
            {
                if(i!=0)
                {
                    i=search(NodeTree.get(i).pFather);//其祖先节点
                }
                else
                    break;
            }
        }
        return false;
    }
    boolean Beta(String str)
    {
        Node nNode=NodeTree.get(search(str));
        if(nNode.pFather==null)  
        {
            return false;
        }

        int i=search(nNode.pFather);
        while(i>=0)
        {
            if((NodeTree.get(i).value<=nNode.value)&&
                    (NodeTree.get(i).leval==MIN)&&((NodeTree.get(i).value!=MAX_INT)))
                            return true;
            else
            {
                if(i!=0)
                {
                    i=search(NodeTree.get(i).pFather);
                }
                else
                    break;
            }
        }
        return false;
    }
    
    public void readTree(String filename)
    {
        File file=new File(filename);
        String nodename[]=new String[10];
        try
        {
            BufferedReader in=new BufferedReader(new FileReader(file));
            String s;
            s=in.readLine();
            if(s.startsWith("ROOT"))
                {
                    nodename=s.split("\\s+");    
                }
            NodeTree.add(new Node(nodename[1]));   
            NodeTree.get(0).leval=MAX;
            NodeTree.get(0).value=MIN_INT;
            NodeTree.get(0).pFather=null;
            while(!(s=in.readLine()).equals("VALUE"))  
            {
                nodename=s.split("\\s+");   
                for(int i=1;i<nodename.length-1;i++) 
                    {
                        NodeTree.get(search(nodename[0])).pChildren.add(nodename[i]);
                        Node nNode=new Node(nodename[i]);  //value为-1；
                        nNode.pFather=nodename[0];        
                        if(NodeTree.get(search(nodename[0])).leval==MAX)  
                        {
                            nNode.leval=MIN;    
                            nNode.value=MAX_INT;
                        }
                        else
                        {
                            nNode.leval=MAX;
                            nNode.value=MIN_INT;
                        }
                        NodeTree.add(nNode);
                    }
            }
            String nodeValue[]=new String[10];
            while(!(s=in.readLine()).equals("END"))
            {
                nodeValue=s.split("\\s+");
                NodeTree.get(search(nodeValue[0])).value=Integer.parseInt(nodeValue[1]);
            }
                in.close();
        }catch(Exception e){
            System.out.println("Error!!");}            
    }
    int search(String str)   
    {
        for(int i=0;i<NodeTree.size();i++)
        {
            if(NodeTree.get(i).name.equals(str))
                return i;
        }
        return -1;
    }
    public static void main(String argv[]){
        String test  = "test.txt";
        new AlphaBeta().getStrategy(test);    
    }
    
}

 

 

//test.txt文件
ROOT A
A     B C END
B     D E END
C     F G END
D     H I END
E     J K END
F     L M END
G     N O END
VALUE
H 4
I 1
J 5
K 0
L 3
M 2
N 7
O 1
END

 

 结果：