Thursday Code Puzzler: Playlist Shuffle Algorithm
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A Reliable Playlist Shuffle Algorithm
One thing I hate is when an implementation of shuffle on a media player results in a song repeating sooner than I would like, or earlier than it should. The challenge today is to write a method that takes a list of Song objects (with title, album and artist fields) and ensures that the space between a song repeating is as much as possible without having the same pattern used if the shuffle goes into a second (or third) run.
Catch up on all our previous puzzlers here.
Comments
Vijay Nathani replied on Sat, 2012/09/08 - 2:44am
Groovy Soluion:
@groovy.transform.Immutable class Song { String title } //album,artist,etc may be added class Shuffle { private def runsTillNow = new LinkedList() private int RUN_HISTORY = 20 def Shuffle(songList) { runsTillNow.add(songList) } private int differenceFromOlderRuns(songs) { int c = runsTillNow.indexOf(songs) + 1 c?c:(RUN_HISTORY+1) //return 1, if songs were just played; return 2, if songs were played before last run; so on } private int howFurtherIsSongJustPlayed(songs) { def s = runsTillNow.first.size() runsTillNow.first.collect{ s-- + songs.indexOf(it) }.min() } def getNextRun() { runsTillNow.addFirst(runsTillNow.first.permutations().max { differenceFromOlderRuns(it) + howFurtherIsSongJustPlayed(it) }) if (runsTillNow.size() > RUN_HISTORY) runsTillNow.pop() runsTillNow.first } } def s = new Shuffle(['t1','t2','t3','t4','t5'].collect { new Song(it) }) 20.times { println s.nextRun }Mohamed Al-habshi replied on Tue, 2012/09/11 - 5:32am
I've made two solutions in Java (Please don't mind the song names. I just made them up).
public class ShuffleSongs { static List<Song> songsList; public static void main(String[] args) { //init list initSongsList(); System.out.println("Before Shuffle"); printSongsList(songsList); //Solution # 1 printSongsList(shuffle1(songsList)); initSongsList(); //Solution # 2 printSongsList(shuffle2(songsList)); } private static void initSongsList() { songsList = new LinkedList<Song>(); songsList.add(new Song("Moon Light", "Nature", "AL")); songsList.add(new Song("Go Next", "Future", "B. J")); songsList.add(new Song("Realllllly", "K", "CCC")); songsList.add(new Song("Fear", "Hell G.", "SD")); songsList.add(new Song("My Dear", "Future", "B. J")); songsList.add(new Song("To the School", "K", "Mike")); songsList.add(new Song("My name is", "Future", "Khan")); songsList.add(new Song("How want some", "Hell G.", "S.Fire")); songsList.add(new Song("My Lord", "K", "Ali")); } private static void printSongsList(List<Song> list){ for (int i = 0; i < list.size(); i++) { Song song = list.get(i); System.out.printf("# %d - Title: %13s | Album: %10s | Artist: %10s\n", i+1, song.title, song.album, song.artist); } System.out.println("--------------------------------------------------------"); } private static List shuffle1(List list){ List res = new LinkedList(); int size = list.size(); int rand = 0; Object[] temp = list.toArray(); int count = 0;; while(count != size){ rand = (int)(Math.random()*list.size()); if(!res.contains(temp[rand])){ res.add(temp[rand]); count++; } } return res; } private static List shuffle2(List list){ if(list.size() == 1){ return list; }else{ int rand = (int)(Math.random()*list.size()); Object o = list.get(rand); list.remove(rand); list = shuffle2(list); list.add(o); return list; } } private static class Song { private String title; private String album; private String artist; public Song() { } public Song(String title, String album, String artist) { this.title = title; this.album = album; this.artist = artist; } }}
Vijay Nathani replied on Tue, 2012/09/11 - 7:37am
in response to:
Mohamed Al-habshi
Joe Colburn replied on Thu, 2012/09/13 - 9:15pm
Here's the function:
$playlists = array(); $tracks = array(); function makePlaylist($tracks) { $played = array(); while (count($tracks) > 0) { $rnd = array_rand($tracks); $played[] = $tracks[$rnd]; unset($tracks[$rnd]); } return $played; }And here's the rest I added in for track list building and testing the function:
class Track { public function setTrack($track_info) { $this->title = $track_info["title"]; $this->album = $track_info["album"]; $this->artist = $track_info["artist"]; return $this; } } for ($i=1; $i < 10; $i++) { $t = new Track(); $tracks[$i] = $t->setTrack(array("title"=>"song $i","album"=>"album $i","artist"=>"artist $i")); } for ($i=1; $i < 8; $i++) { $playlists[] = makePlaylist($tracks); } foreach ($playlists as $key => $pl) { echo "<b>Playlist #$key</b><br />"; foreach ($pl as $idx => $track) { echo " - ".$track->title." by ".$track->artist." from the album ".$track->album."<br />"; } }