[백준] 1822번 차집합 (silver 4

import java.io.*;
import java.util.*;
public class Main{
    public static void main(String[] args) throws IOException{
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw=new BufferedWriter(new OutputStreamWriter(System.out));
        StringTokenizer st=new StringTokenizer(br.readLine());
        int a=Integer.valueOf(st.nextToken());
        int b=Integer.valueOf(st.nextToken());

        String input=br.readLine();

        HashMap<Integer,Integer> dict=new HashMap<>();
        st=new StringTokenizer(br.readLine());
        for(int i=0; i<b; i++){
            dict.put(Integer.valueOf(st.nextToken()),2);
        }
        st=new StringTokenizer(input);

        ArrayList<Integer> arr=new ArrayList<>();
        for(int i=0; i<a; i++){
            int temp=Integer.valueOf(st.nextToken());
            if(dict.get(temp)==null){
                arr.add(temp);
            }
        }
        Collections.sort(arr);
        if(arr.size()==0){
            bw.write("0");
        }
        else{
            bw.write(arr.size()+"\n");
            for(Integer e: arr){
                bw.write(e+" ");
            }
        }
        bw.flush();
    }
}