First, a short phone call to introduce myself and my background.

Then, a technical interview on Zoom where I was asked to explain my experience and solve a practical coding task.

I was given a data structure representing users and their associated teams: users = { 1: { id: 1, name: 'user1', teams: [1, 2] }, 2: { id: 2, name: 'user2', teams: [1] }, ... }

Along with several black-box functions such as getUsers() - which returns an array of recipients (users and teams) that should receive a specific notification: [ { type: 'user', id: 1 }, { type: 'team', id: 2 }, ... ]

The task was to implement two functions: notifyUsers(userId, msg) - sends a message to a specific user. notification(msg) - which uses notifyUsers to send the message to all users and teams returned by getUsers().

Requirements: Optimize the implementation to handle millions of users and teams efficiently. Avoid redundant notifications (e.g., if a user belongs to multiple teams). Discuss time and space complexity, scalability, and potential batching strategies.