PAT L1-011. A-B

import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc=new Scanner(System.in);
        String str1=sc.nextLine();
        String str2=sc.nextLine();
        char[]ch1=str1.toCharArray();
        
        String str="";
        out:for(char i:ch1){
        	
        	if(str2.contains(String.valueOf(i))){
                        continue out;            		
        	}else{
       	                str+=i;
             }
        	
        }
        System.out.println(str);
	}

}
第二种方法，还是运行超时。。

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;


public class Main {

	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
           Scanner sc=new Scanner(System.in);
           BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
           
           String str1=br.readLine();
           String str2=br.readLine();
           char []ch=str2.toCharArray();
           String str[]=new String[ch.length];
           String str3="";
           String str4="";
           for(int i=0;i<ch.length;i++){
        	
        	   str[i]=str3.valueOf(ch[i]);
        	   //System.out.println(str[i]);
        	   str4=str1.replace(str[i],"");
        	   str1=str4;
           }
           
           
           System.out.println(str4);
	}

}