240212 베스트앨범

public int[] solution(String[] genres, int[] plays) {
	List<String> sortedGenres = sortByTotalPlays(genres, plays);

	List<Integer> resultIndices = new ArrayList<>();
	for (String genre : sortedGenres) {
		int firstIdx = findMostPlayedSongIndex(genres, plays, genre);
		resultIndices.add(firstIdx);

		int secondIdx = findMostPlayedSongIndexExceptGivenIndex(genres, plays, genre, firstIdx);
		if (secondIdx != -1)
			resultIndices.add(secondIdx);
	}

	int[] result = new int[resultIndices.size()];
	for (int i = 0; i < resultIndices.size(); i++) {
		result[i] = resultIndices.get(i);
	}
	return result;
}

private List<String> sortByTotalPlays(String[] genres, int[] plays) {
	Map<String, Integer> genreTotalPlaysMap = new HashMap<>();
	for (int i = 0; i < genres.length; i++) {
		genreTotalPlaysMap.put(genres[i], genreTotalPlaysMap.getOrDefault(genres[i], 0) + plays[i]);
	}
	List<String> sortedGenres = new ArrayList<>(genreTotalPlaysMap.keySet());
	sortedGenres.sort((genre1, genre2) -> genreTotalPlaysMap.get(genre2) - genreTotalPlaysMap.get(genre1));
	return sortedGenres;
}

private int findMostPlayedSongIndex(String[] genres, int[] plays, String genre) {
	int maxPlays = 0;
	int mostPlayedIndex = -1;
	for (int i = 0; i < genres.length; i++) {
		if (genres[i].equals(genre) && plays[i] > maxPlays) {
			maxPlays = plays[i];
			mostPlayedIndex = i;
		}
	}
	return mostPlayedIndex;
}

private int findMostPlayedSongIndexExceptGivenIndex(String[] genres, int[] plays, String genre, int exceptIndex) {
	int maxPlays = 0;
	int secondMostPlayedIndex = -1;
	for (int i = 0; i < genres.length; i++) {
		if (genres[i].equals(genre) && plays[i] > maxPlays && i != exceptIndex) {
			maxPlays = plays[i];
			secondMostPlayedIndex = i;
		}
	}
	return secondMostPlayedIndex;
}

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