How would you create a playlist for a user after they listen to a single song? (in an app like Spotify)

Clarification

Going to assume we are Spotify and that this is an individual consumer account and not an account used by a business like a restaurant or a bar. The user could be listening from their computer, our mobile app, or their car which may be helpful information but our task at hand is the same. 

Goal

Before we dive into the problem, let's first take a step back and think about why are we doing this and what are we hoping to accomplish. Is there some sort of strategic initiative we need to align with or was there a specific goal in mind?

If the interviewer doesn't have anything planned we can devise this ourselves by examining Spotify's mission statement which is to unlock human creativity and give artists the ability live off of their art.

By making recommendations we help users listen to more music and get the creative juices flowing while simultaneously paying the artists for the ability to play their music.

If we can increase the amount of time users spend listening to music we can further our mission statement so let's focus on that as a goal.

User Segments

It's hard to come up with a magic bullet that solves everything for everyone so one of the ways I like to narrow scope is by looking at different user segments and choosing one to prioritize:

1. Musicians - In addition to playing music they also listen to it obviously. Expert level understanding of music and a better sense of what is "good" music.
2. Top 20 Fans - Generally like catchy songs and different genres, whatever the flavor of the month is
3. Fan Boy / Girl - Zealous followers of an individual artist or group, aka Swifties or BTS Fans
4. Genre Experts - Individuals who are really passionate about a specific genre of music, for example hip hop heads

1. The song is not in their genre of preference
2. The song is way too overplayed / they're sick of it
3. The song doesn't match their current setting, listening to music at the gym is very different from the library

1. Preliminary Music Taste Survey - As part of the onboarding process users could optionally fill out a survey regarding their music tastes and preferences which we would then use to make our initial song recommendations.
2. Import Listening History - We could let users import their listening history from other platforms like Pandora and Apple Music which would then give us a very good sense of what they would like to listen to.
3. Friend Music Preferences Informed Algorithm - When users sign up, they could upload their contacts and mark which of their friends with spotify accounts they think have good taste in music. 
4. Grant Access to User Personal Data - After signing up, users could give us permission to access some of their data from other apps like Facebook and we could make informed  music recommendations based off of that. For example, if we saw that you liked the Metallica FB Page it would be a pretty strong signal to put Metallica songs in your play list.

This is how I plan to approach the prompt:

1) Ask follow up questions to understand the prompt better and establish the business goal

2) Define user segments and select one to focus on

3) Brainstorm attributes to focus on for creating a playlist feature

4) Conclude

Follow up questions

Candidate: Is the goal to improve the user engagement with the app in terms of time spent, by curating a music content that users enjoy

Interviewer: Sounds good

Candidate: Will it be built only specific segment of users, viz a) free or paid users b) guest users or registered users c) kids vs adults (digital well being best practise is to turn off an autoplay or playlist feature for kids, because they do not have full developed self-control capacities) 

Interviewer: This feature is applicable to all 18+ users 

Candidate: Will playlist contain songs excusively or mix of songs and other content forms such as podcasts?

Interviewer: only songs

User segments

A) First timers

B) Causual users

C) Heavy users

Heavy users are already engaged well with the app, I will create feature around a first time users

Attributes/inputs into the playlist feature

I would like to outline the key attributes that I would use to build a playlist and then I will curate the list of songs align with these attributes and then rank them based on how strongly they align with these attributes.

A) Language: In order to fully appreciate and enjoy the music, it is critical that user can understand the language. Therefore, I would ensure the playlist contents match with the laguage of the first song

B) Genre: User will enjoy the content the most, when we are able to capture their mood. I would use first song as a signal as to the genre that they want to listen to, and that fit their current mood

C) Artist: Users tend to have favorite artists and content from their favorite artists bring them more joy. Therefore I would weight songs from the same artists in building the playlist. 

D) Interests expressed by the user: To better understand the user preferences and their tastes better, I would like to collect likes and interests expressed by the user on social media such as facebook, instagram, twitter. This can be done by linking the spotify and social media profiles together.

E) Most listened next song/content by other users: Based on the historical data, I would identify the most listened next song among the other users, given the first song that is playing. I woud this insight as one of the key input when building a playlist

F) Popularity of the music: More often than not, users tend to enjoy the popular songs. So I would use popularity of the songs as one of the key signal in building a playlist.

Conclude

We established the business goal, defined the user segments that we want to prioritize as we plan to build the playlist feature, then outlined mental model for creating a playlist and detailed the attributes that the playlist will be based off of.