算法强化每日一题--删除公共字符

public class TestDemo {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        String s1=in.nextLine();
        String s2=in.nextLine();
        Set<Character> set=new HashSet<>();
        StringBuffer stringBuffer=new StringBuffer();//拼接字符串
        for(int i=0;i<s2.length();i++) {
            char ch = s2.charAt(i);
            set.add(ch);
        }
            for(int j=0;j<s1.length();j++){
                char ch1=s1.charAt(j);
                if(!set.contains(ch1)){
                    stringBuffer.append(ch1);
                }
            }
        System.out.println(stringBuffer);
    }
}

import java.util.HashMap;
import java.util.Scanner;
public class Test {
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        String s1=scanner.nextLine();
        String s2=scanner.nextLine();
        HashMap<Character,Integer> hashMap=new HashMap<>();
        //遍历第二个数组
        for(int i=0;i<s2.length();i++){
            if(hashMap.get(s2.charAt(i))==null){
                hashMap.put(s2.charAt(i),1);
            }else{
                hashMap.put(s2.charAt(i),hashMap.get(s2.charAt(i))+1);
            }
    }
        //遍历第一个数组
        String ret="";
        for(int i=0;i<s1.length();i++){
            if(hashMap.get(s1.charAt(i))==null){
                ret+=s1.charAt(i);
            }
        }
        System.out.println(ret);
    }
}