프로그래머스 베스트앨범

import java.util.concurrent.atomic.AtomicInteger;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.*;

import static java.util.stream.Collectors.*;


public class algo {

    public static void main(String[] args) {
        String[] genres = {"classic", "pop", "classic", "classic", "pop"};
        int[] plays = {500, 600, 150, 800, 2500};

        solution(genres, plays);
    }

    public static class Music implements Comparable<Music> {
        private String genre;
        private int played;
        private int id;

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

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

        public String getGenre() {
            return genre;
        }
    }

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

    public static 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();
    }
}