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Write queries for follows and bookings | Meta Interview Question

Q: Write queries for follows and bookings

This question evaluates the ability to manipulate temporal event logs, enforce bidirectional relational integrity, and implement efficient graph and interval algorithms using SQL and Python.

You are given tables/logs from a consumer app. Solve the following independent tasks.

Part A — Active following as of a date (SQL)

You have a follow event log:

follow_events(follower_id, followee_id, event_type, event_ts)
event_type ∈ {'follow','unfollow'}
A user can follow/unfollow the same person multiple times.

Task: Given a parameter date D (inclusive), return all active follow relationships at the end of day D (i.e., after all events with event_ts <= D 23:59:59).

Output columns:

as_of_date (value = D ), follower_id , followee_id

Clarifications/edge cases to handle:

If the latest event on or before D is follow , the relationship is active.
If the latest event is unfollow , it is inactive.
If there are no events on/before D , it should not appear.

Part B — Add reciprocal friendships (SQL)

You have a directed friendship table:

friendships(user_id, friend_id)

A friendship should be bidirectional (if (A,B) exists, (B,A) should also exist).

Task: Produce the set of missing reciprocal rows that must be inserted to make the data bidirectional, without creating duplicates.

Output columns: user_id, friend_id representing rows to insert.

Part C — Mutual friends (Python)

You are given an undirected friendship list edges, where each element is a pair (u, v) meaning u and v are friends.

Task: Implement a function that returns the set (or sorted list) of mutual friends of two users a and b.

Constraints to consider:

The graph can be large; aim for an efficient approach.

Part D — Valid car bookings (Python)

A single car can be booked by only one customer at a time.

You are given booking requests as a list of tuples (booking_id, start_time, end_time), where start_time < end_time.

Rule: Accept bookings in increasing start_time order; a booking is valid/accepted if it does not overlap with any previously accepted booking.

Task: Return the list of accepted booking_ids.

Edge cases:

Back-to-back bookings where end_time == next_start_time do not overlap.
Input may be unsorted.

You are given tables/logs from a consumer app. Solve the following independent tasks.

Part A — Active following as of a date (SQL)

You have a follow event log:

follow_events(follower_id, followee_id, event_type, event_ts)
event_type ∈ {'follow','unfollow'}
A user can follow/unfollow the same person multiple times.

Task: Given a parameter date D (inclusive), return all active follow relationships at the end of day D (i.e., after all events with event_ts <= D 23:59:59).

Output columns:

as_of_date (value = D ), follower_id , followee_id

Clarifications/edge cases to handle:

If the latest event on or before D is follow , the relationship is active.
If the latest event is unfollow , it is inactive.
If there are no events on/before D , it should not appear.

Part B — Add reciprocal friendships (SQL)

You have a directed friendship table:

friendships(user_id, friend_id)

A friendship should be bidirectional (if (A,B) exists, (B,A) should also exist).

Task: Produce the set of missing reciprocal rows that must be inserted to make the data bidirectional, without creating duplicates.

Output columns: user_id, friend_id representing rows to insert.

Part C — Mutual friends (Python)

You are given an undirected friendship list edges, where each element is a pair (u, v) meaning u and v are friends.

Task: Implement a function that returns the set (or sorted list) of mutual friends of two users a and b.

Constraints to consider:

The graph can be large; aim for an efficient approach.

Part D — Valid car bookings (Python)

A single car can be booked by only one customer at a time.

You are given booking requests as a list of tuples (booking_id, start_time, end_time), where start_time < end_time.

Rule: Accept bookings in increasing start_time order; a booking is valid/accepted if it does not overlap with any previously accepted booking.

Task: Return the list of accepted booking_ids.

Edge cases:

Back-to-back bookings where end_time == next_start_time do not overlap.
Input may be unsorted.

Write queries for follows and bookings

Quick Overview

Part A — Active following as of a date (SQL)

Part B — Add reciprocal friendships (SQL)

Part C — Mutual friends (Python)

Part D — Valid car bookings (Python)

Comments (0)

Write queries for follows and bookings

Quick Overview

Part A — Active following as of a date (SQL)

Part B — Add reciprocal friendships (SQL)

Part C — Mutual friends (Python)

Part D — Valid car bookings (Python)

Comments (0)