[프로그래머스] 베스트앨범

https://programmers.co.kr/learn/courses/30/lessons/42579

코딩테스트 연습 - 베스트앨범

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[ 나의 풀이 ]

import java.util.List;
import java.util.ArrayList;
import java.util.Map;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.Arrays;

class Solution {
    public int[] solution(String[] genres, int[] plays) {
        Map<String, Map<Integer, Integer>> musics = new HashMap<>();
        Map<String, Integer> totals = new HashMap<>();
        Map<Integer, Integer> playMap = null;
        String genre = "";

        for(int i = 0; i < genres.length; i++){
            genre = genres[i];

            totals.put(genre, totals.getOrDefault(genre,0) + plays[i]); //장르별 플레이 수 총 합 저장

            playMap = musics.getOrDefault(genre, new HashMap<>()); //장르별 인덱스 리스트 저장
            playMap.put(i, plays[i]);
            musics.put(genre, playMap);
        }

        List<Map.Entry<String, Integer>> entries = new LinkedList<>(totals.entrySet()); //장르별 플레이 수 정렬
        Collections.sort(entries, (o1, o2) -> o2.getValue().compareTo(o1.getValue()));

        Map<Integer, Integer> musicMap = null;
        List<Integer> result = new ArrayList<>();
        for(Map.Entry<String, Integer> entry : entries) {
            musicMap = musics.get(entry.getKey());
            List<Map.Entry<Integer, Integer>> musicEntries = new LinkedList<>(musicMap.entrySet());
            Collections.sort(musicEntries, ((o1, o2) -> o2.getValue().compareTo(o1.getValue())));

            if(musicEntries.size() > 2) {
                musicEntries = musicEntries.subList(0,2);
            }
            for(Map.Entry<Integer, Integer> musicEntry : musicEntries) {
                result.add(musicEntry.getKey());
            }
        }



        int[] answer = result.stream().
                mapToInt(i -> i).toArray();
        return answer;
    }
}

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[ Stream을 이용한 풀이 ]

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

class Solution {
    public int[] solution(String[] genres, int[] plays) {
        return IntStream.range(0, genres.length) // genre 길이만큼 stream
                .mapToObj(i -> new Music(genres[i], plays[i], i)) // Music object map put
                .collect(Collectors.groupingBy(Music::getGenre)) // genre로 grouping
                .entrySet().stream() // entryset stream
                .sorted((a, b) -> sum(b.getValue()) - sum(a.getValue())) // sum기준 sorting
                .flatMap(x -> x.getValue().stream().sorted().limit(2)) // 각 value 2개 까지 sorting
                .mapToInt(x -> x.id).toArray(); // id를 array로 mapping
    }
    
    public class Music implements Comparable<Music> {

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

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

        public String getGenre() {
            return genre;
        }

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

        @Override
        public String toString() {
            return "Music{" +
                    "played=" + played +
                    ", id=" + id +
                    ", genre='" + genre + '\'' +
                    '}';
        }
    }

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