Hash - 베스트 앨범

import java.util.*;

class Solution {
    public int[] solution(String[] genres, int[] plays) {
        int[] answer = {};
        
        ArrayList<Integer> answerList = new ArrayList<>();
        
        HashMap<String, GenreInfo> genreInfoByName = new HashMap<>();
        
        for (int i=0; i<genres.length; i++) {
            // 장르별 정보
            genreInfoByName.putIfAbsent(genres[i], new GenreInfo(genres[i]));
            genreInfoByName.get(genres[i]).addMusic(new Music(i, genres[i], plays[i]));
        }
        
        ArrayList<GenreInfo> genreInfoList = new ArrayList<>(genreInfoByName.values());
        
        Collections.sort(genreInfoList);
        
        for (GenreInfo genreInfo : genreInfoList) {
            genreInfo.sortMusic();
            answerList.add(genreInfo.getMusic(0).id);
            if (genreInfo.getCount() > 1) {
                answerList.add(genreInfo.getMusic(1).id);
            }
        }
        
        int[] answerArray = new int[answerList.size()];
            int index = 0;
            for (int id : answerList) {
                answerArray[index++] = id;
            }
            
            answer = answerArray;
        
        return answer;
    }
}

class Music implements Comparable {
        int id;
        String genre;
        int play;

        Music(int id, String genre, int play) {
            this.id = id;
            this.genre = genre;
            this.play = play;
        }

        public int getId() {
            return this.id;
        }

        public String getGenre() {
            return this.genre;
        }

        public int getPlay() {
            return this.play;
        }

        @Override
        public int compareTo(Object object) {
            Music otherMusic = (Music) object;
            if (otherMusic.play == this.play) {
                return this.id - otherMusic.id;
            }
            return otherMusic.play - this.play; // 내림차순
        }
    }

class GenreInfo implements Comparable {
    
    final String genre;
    
    private final ArrayList<Music> musics = new ArrayList<>();
    
    GenreInfo(String genre) {
        this.genre = genre;
    }
    
    public void addMusic(Music music) {
        this.musics.add(music);
    }
    
    public int getCount() {
        return this.musics.size();
    }
    
    public int totalPlays() {
        int count = 0;
        for (Music music : musics) {
            count += music.play;
        }
        return count;
    }
    
    public void sortMusic() {
        Collections.sort(musics);
    }
    
    public ArrayList<Music> getMusics() {
        return this.musics;
    }
    
    public Music getMusic(int index) {
        return this.musics.get(index);
    }
    
    @Override
    public int compareTo(Object otherInfo) {
        return ((GenreInfo) otherInfo).totalPlays() - this.totalPlays();
    }
    
}