[Lv.3] 베스트 앨범

내가 짠 코드(통과)

import java.util.*;

class Solution {
    public int[] solution(String[] genres, int[] plays) {
        int[] answer = {};
        Map<String,Genre> genreMap=new HashMap<String,Genre>();
        List<Genre> genreList=new ArrayList<Genre>();
        //key: name
        for (int i=0;i<genres.length;i++) {
            String name=genres[i];
            if(genreMap.get(name)==null){
                Genre gen=new Genre(name);
                gen.indexList.add(i);
                gen.genrePlaySum=plays[i];
                genreMap.put(name,gen);
                genreList.add(gen);
            }else{
                Genre genre = genreMap.get(name);
                genre.indexList.add(i);
                genre.genrePlaySum+=plays[i];
            }
        }
//        genreMap.forEach((s, genre) -> {
//            System.out.println("s = " + s);
//            System.out.println("genre = " + genre);
//        });
        //System.out.println("================================================================");

        List<Integer> ansList=new ArrayList<Integer>();
        //인기 장르 순 배치
        Collections.sort(genreList, new Comparator<Genre>() {
            @Override
            public int compare(Genre o1, Genre o2) {
                return o2.genrePlaySum-o1.genrePlaySum;
            }
        });
        //genreList.forEach(genre -> System.out.println("genre = " + genre));
        //장르별 top2 선정 및 add to answer
        for (Genre genre : genreList) {
            int top1,top2;
            top1=top2=-1;
            int top1Value,top2Value;
            top1Value=top2Value=-1;
            //System.out.println("now : genre = " + genre);
            for (Integer integer : genre.indexList) {
                //System.out.println("now integer: " + integer);
                if(plays[integer]>top1Value){
                    //System.out.println("new top1");
                    if(top1!=-1){
                        //System.out.println("top1 go to top2");
                        top2=top1;
                        top2Value = top1Value;
                    }
                    top1=integer;
                    top1Value=plays[integer];
                }else if(plays[integer]>top2Value){
                    //System.out.println("new top2");
                    top2=integer;
                    top2Value=plays[integer];
                }
            }
            ansList.add(top1);
            if(top2!=-1)
                ansList.add(top2);
        }

        return ansList.stream().mapToInt(i->i).toArray();
    }
    class Genre{
        String name;

        @Override
        public String toString() {
            return "Genre{" +
                    "name='" + name + '\'' +
                    ", indexList=" + indexList +
                    ", genrePlaySum=" + genrePlaySum +
                    '}';
        }

        List<Integer> indexList=new ArrayList<>();
        int genrePlaySum=0;

        public Genre(String name) {
            this.name = name;
        }
    }
}

다른 분이 짠 스트림 활용2000% 코드

import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class Solution {
  public class Music implements Comparable<Music>{

    private int played;
    private int id;
    private String genre;

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

    @Override
    public int compareTo(Music other) {
      if(this.played == other.played) return this.id - other.id;
      return other.played - this.played;
    }

    public String getGenre() {return genre;}
  }

  public int[] solution(String[] genres, int[] plays) {
    return IntStream.range(0, genres.length)
    .mapToObj(i -> new Music(genres[i], plays[i], i))
    .collect(Collectors.groupingBy(Music::getGenre))
    .entrySet().stream()
    .sorted((a, b) -> sum(b.getValue()) - sum(a.getValue()))
    .flatMap(x->x.getValue().stream().sorted().limit(2))
    .mapToInt(x->x.id).toArray();
  }

  private int sum(List<Music> value) {
    int answer = 0;
    for (Music music : value) {
      answer+=music.played;
    }
    return answer;
  }
}

---

문제 자체는 평이했다.

근데, 통과 후 다른 사람의 풀이를 보니 스트림 활용을 저렇게도 할 수 있구나 싶은 코드가 나와 같이 올렸다 !

스트림.. 공부 좀 더 해야겠다