人工智能之一般合一算法Java实现之

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class Unify {
    private static String EMPTY = " ";
    private static String FAIL = "Failed";
    private static List<String> list1 = new ArrayList<String>();
    private static List<String> list2 = new ArrayList<String>();
    
    public static void main(String[] args){
        //输入两个谓词公式
        System.out.println("请输入待判断的两个表达式，变量用小写字母表示，常量用大写字符或字符串表示。");
        Scanner input = new Scanner(System.in);
        String E1 = input.nextLine();
        list1 = Unify.getElements(E1);
        String E2 = input.nextLine();
        list2 = Unify.getElements(E2);
        System.out.println("最一般的表达式为：" + Unify.unify(E1, E2));
    }
    
    private static List<String> getElements(String E){
        List<String> list = new ArrayList<String>();
        for(int i = 0; i < E.length(); i++){
            if(E.charAt(i) == ')')
                list.add("()");
            if((E.charAt(i) >= 'a' && E.charAt(i) <= 'z') || (E.charAt(i) >= 'A' && E.charAt(i) <= 'Z')){
                int j = i+1;
                while(j < E.length() && ((E.charAt(j) >= 'a' && E.charAt(j) <= 'z') || (E.charAt(j) >= 'A' && E.charAt(j) <= 'Z')))
                    j++;
                list.add(E.substring(i,j));//取出'('和')'之间的串
                i = j - 1;
            }
        }
        return list;
    }
    
    private static String unify(String E1, String E2){
         if(E1.isEmpty() && E2.isEmpty())
             return Unify.EMPTY;
         if(Unify.isConstants(E1) && Unify.isConstants(E2)){
             if(E1.equals(E2))
                 return Unify.EMPTY;
             else
                 return Unify.FAIL;
         }
         
         if(Unify.isVariable(E1)){
             //contains()方法,当且仅当此字符串包含指定的char值序列时,返回true
             if(!E2.equals(E1) && E2.contains(E1))
                 return Unify.FAIL;
             else{
                 if(E2.equals(E1))//判断是否相等
                     return Unify.EMPTY;
                 else
                     return E2 + "/" + E1;                     
             } 
         }
         
         if(Unify.isVariable(E2)){
             if(!E1.equals(E2) && E1.contains(E2))
                 return Unify.FAIL;
             else{
                 if(E2.equals(E1))
                     return Unify.EMPTY;
                 else
                     return E1 + "/" + E2;
             }
         }
         
         if(E1.isEmpty() || E2.isEmpty())
             return Unify.FAIL;
         else{
             String he1 = Unify.getFirstElement(list1);
             E1 = Unify.getRest(E1, he1);
             String he2 = Unify.getFirstElement(list2);
             E2 = Unify.getRest(E2, he2);
             String subs1 = Unify.unify(he1, he2);
             if(subs1.equals(Unify.FAIL))
                 return Unify.FAIL;
             String te1 = Unify.apply(subs1, E1, list1);
             String te2 = Unify.apply(subs1, E2, list2);
             String subs2 = Unify.unify(te1, te2);
             if(subs1.equals(Unify.FAIL))
                 return Unify.FAIL;
             else
                 return Unify.composition(subs1, subs2);
         }
    }
    //判断常量
    private static boolean isConstants(String E){
        if(!E.isEmpty()){
            if(E.length() > 1){
                if(E.equals("()"))
                    return true;
                if(E.contains(" ") || E.contains("(") || E.contains(")") || E.contains(","))
                    return false;
                else
                    return true;
            }
            else{
                if(E.charAt(0)>='A' && E.charAt(0) <= 'Z')
                    return true;
                else
                    return false;                
            }
        }
        return false;
    }
    //判断变量
    
    private static boolean isVariable(String E){
        if(!E.isEmpty()){
            if(E.length() > 1){
                if(E.contains(" ") || E.contains("(") || E.contains(")") || E.contains(","))
                    return false;
                else
                    return true;
            }
            else{
                if(E.charAt(0)>='a' && E.charAt(0) <= 'z')
                    return true;
                else
                    return false;                
            }
        }
        return false;
    }
    
    private static String getFirstElement(List<String> list){
        String element = list.get(0);
        list.remove(0);
        return element;
    }
    //该函数查找s2在E中的位置并用s1替代E中相应的s2
    private static String apply(String subs1, String E, List<String> list){
        if(subs1.equals(Unify.EMPTY))
            return E;
        String sub1 = subs1.substring(0, subs1.indexOf('/'));
        String sub2 = subs1.substring(subs1.indexOf('/') + 1, subs1.length());
        E = E.replaceAll(sub2, sub1);
        for(int i = 0; i < list.size(); i++){
            if(list.get(i).equals(sub2))
                list.set(i, sub1);
        }
        return E;
    }
    
    private static String composition(String subs1, String subs2){
        if(subs1.equals(Unify.EMPTY) && subs2.equals(Unify.EMPTY))
            return Unify.EMPTY;
        else if(subs1.equals(Unify.EMPTY))
            return subs2;
        else if(subs2.equals(Unify.EMPTY))
            return subs1;
        else 
            return subs1 + ", " + subs2;
    }
    
    private static String getRest(String E, String firstElement){
        if(!E.isEmpty()){
            String e;
            if(firstElement.equals("()"))
                e = E.replaceFirst("\\(\\)","0");
            else
                e = E.replaceFirst(firstElement,"0");
            if(e.length() == 1)
                return "";
            int i = e.indexOf('0');
            int j = i + 1;
            while(e.charAt(j) == ' ' || e.charAt(j) == ',')
                j++;
            e = e.substring(0, i) + e.substring(j);
            return e;
        }
        return null;
    }
}