[백준 1764/해시] 실버4/듣보잡 (자바)

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

class Main {
    public static void main(String[] args) throws IOException {
        // 0. 입력 및 초기화
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
        
        StringTokenizer st = new StringTokenizer(br.readLine());
        int N = Integer.parseInt(st.nextToken());
        int M = Integer.parseInt(st.nextToken());
        
        // 1. hash 에 듣도 못한 사람 저장("이름": 1)
        HashMap<String, Integer> hashMap = new HashMap<>();
        for(int i=0; i<N; i++) {
            hashMap.put(br.readLine(), 1);
        }
        // 2. hash 에 보도 못한 사람 찾기
        List<String> answer = new ArrayList<>();
        for(int i=0; i<M; i++) {
            String noSeePerson = br.readLine();
            if(hashMap.containsKey(noSeePerson)) {
                answer.add(noSeePerson);
            }
        }
        
        // 3. 출력
         Collections.sort(answer);
        System.out.println(answer.size());
        for (String s : answer) {
            System.out.println(s);
        }
        br.close();
    }
}