Instructions

Ozan is putting together a playlist for an upcoming roadtrip. He doesn't want to hear the same track more than once, but the playlist has gotten so long that he's having trouble remembering which tracks have already been added.

The API for Ozan's music player only knows how to work with arrays, so he attempts to write some code that uses Array.indexOf() to check for the presence of a track before adding it to the playlist. Unfortunately, his program takes much too long to execute. He needs your help!

Coming to Ozan's aid, you are astonished to find that his playlist contains half a million tracks. Perhaps you know of a different data structure that will allow you to manipulate the playlist more efficiently?

1. Remove duplicate tracks

Implement the removeDuplicates function, which takes a playlist as a parameter and returns a new playlist where all the tracks are unique.

2. Check whether a track has already been added

Implement the hasTrack function, which takes a playlist and a track as parameters and returns a boolean that indicates whether the playlist contains the track.

3. Add a track

Implement the addTrack function, which takes a playlist and a track as parameters and returns a new playlist that includes the track.

4. Delete a track

Implement the deleteTrack function, which takes a playlist and a track as parameters and returns a new playlist that does not include the track.

5. List unique artists

Implement the listArtists function, which takes a playlist as a parameter and returns the list of unique artists in the playlist. Note that the names of the tracks are formatted like <SONG> - <ARTIST>.