The problem statement was short enough that I had to print out the data structure just to figure out what I was working with.
First, clarify the problem constraints and edge cases, then propose an efficient algorithm. A strong approach is to filter flights for the given user, sort them by departure time, and use binary search to find the relevant flight interval, handling the specified cases explicitly.
Pro tip: Mention that you would preprocess the flight data by grouping flights per user and sorting them, which allows O(log n) queries after O(n log n) preprocessing. This shows you think about scalability and real-world usage where multiple queries might be made.
Ask questions to confirm assumptions: Are flights sorted? Can flights overlap? What if the user has no flights? Should the timestamp be inclusive/exclusive? This demonstrates attention to detail and adaptability.
Explain that you will filter flights for the user, sort them by departure time, and then determine the user's location based on the timestamp relative to flight intervals. Use binary search for efficiency.
Explicitly describe how to handle: before first departure (return departure airport of first flight? Actually, if before any flights, return empty string? Wait, the problem says 'before any flights depart' - likely return empty string? But the problem says 'handle cases like: before any flights depart, between consecutive flights, and after the last flight lands.' It doesn't specify what to return for before/after. Typically, before first flight, user is at departure airport of first flight? Or maybe empty? The problem says 'returns which airport that user is currently at. Return an empty string if the user is mid-flight'. So for before any flights, if user hasn't started traveling, they might be at home? But we don't know. Probably return empty string? But the problem says 'handle cases like: before any flights depart, between consecutive flights, and after the last flight lands.' It might imply that for before first flight, return the departure airport of the first flight? Or maybe the user is at the departure airport of the first flight? Actually, if the user is before any flights, they are at the departure airport of the first flight? But that's an assumption. Let's read carefully: 'Given a list of flight records... write a function that takes a user ID and a timestamp and returns which airport that user is currently at. Return an empty string if the user is mid-flight, and handle cases like: before any flights depart, between consecutive flights, and after the last flight lands.' So the cases to handle are: before any flights depart (timestamp before first departure), between consecutive flights (timestamp after arrival of one flight and before departure of next), and after the last flight lands (timestamp after last arrival). For these, the user is at an airport: before first departure, they are at the departure airport of the first flight? Or maybe they are at the arrival airport of the previous flight? But there is no previous. So likely, before first departure, they are at the departure airport of the first flight. Between flights, they are at the arrival airport of the previous flight (which should equal departure airport of next flight if no gap? Actually, between consecutive flights, they are at the airport where they landed from the previous flight, which is the arrival airport of the previous flight. After last flight, they are at the arrival airport of the last flight. So the function should return the airport where the user is located at that timestamp. If mid-flight, return empty string. So for before first departure, they are at the departure airport of the first flight? But that assumes they are at the airport before the flight. That seems reasonable. So we need to handle: if timestamp < first departure, return first departure airport? Or maybe empty? The problem says 'handle cases like: before any flights depart' - so we need to decide. I'll assume return the departure airport of the first flight. But we should clarify with interviewer. So in step 3, describe how to handle each case: before first flight -> departure airport of first flight; between flights -> arrival airport of previous flight; after last flight -> arrival airport of last flight; mid-flight -> empty string.
Write clean code with clear variable names, and walk through test cases including edge cases (no flights, exactly at departure/arrival times, etc.).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.