The "Leetcodify Similar Friends interview question" is a database query challenge that focuses on identifying "similarity" between existing friends. In this scenario, you are given a platform where users can follow each other and listen to songs. Your task is to find pairs of users who are already friends and have listened to at least three common songs on the same day. This "Leetcodify Similar Friends coding problem" is a variation of recommendation systems, where instead of suggesting new friends, you are analyzing the strength or shared interests of existing connections.
This problem is frequently used in interviews for Data Engineering or Backend roles at companies like Spotify. It evaluates your ability to handle complex relational data using "Database interview pattern" techniques. Specifically, it tests your proficiency in joining multiple tables (Users, Listens, and Friendships) and applying multi-level filtering. It also assesses how well you can handle non-trivial conditions like "on the same day" and "at least three common songs."
The primary pattern here is the application of SQL Relational Joins and Set Intersection. You first need to identify all (User1, User2) pairs who are friends by joining the Friendship table. Then, you join this result with the Listens table twice—once for User1 and once for User2—on the song ID and the date. This allows you to count how many songs they listened to together on each specific day.
Imagine User X and User Y are friends. On 2023-11-15:
When working with SQL-based interview questions, always draw out a small schema and trace the join logic manually. Pay close attention to aggregation levels—knowing whether you are grouping by user, by day, or by both is key to solving these types of problems correctly.
