Implement Due Broadcast Sender
Company: Attentive
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Technical Screen
You are building a notification system.
You are given:
- A mapping from `company_id` to a list of subscriber IDs.
- A list of broadcast logs. Each log contains:
- `log_id`
- `company_id`
- `message`
- `scheduled_at`
- a flag or status indicating whether it has already been sent.
- A helper function `send_subscriber_msg(subscriber_id, message)`.
Implement code that sends a broadcast message to all subscribers of the specified company when the broadcast becomes due.
Your design should support two variants:
1. The function receives a single `current_time` and should send all broadcasts with `scheduled_at <= current_time` that have not yet been processed.
2. The function receives a time window `[start_time, end_time]` and should send all broadcasts whose scheduled time falls within that range.
Clarify the input structures you choose, how you avoid duplicate sends, and how you update processing state after delivery.
Quick Answer: This question evaluates a candidate's ability to implement time-based broadcast delivery, including filtering by time windows, idempotent state updates to prevent duplicate sends, and managing concurrency and data structures for processing and tracking broadcast logs.
Part 1: Send Due Broadcasts Up To current_time
You are building a notification system for multiple companies. Each company has a list of subscriber IDs, and each broadcast log describes one message that may need to be sent.
Implement a function that processes all broadcast logs whose `scheduled_at` time is less than or equal to `current_time`, but only if they have not already been sent.
Because coding platforms usually cannot verify real side effects, simulate `send_subscriber_msg(subscriber_id, message)` by recording each delivery as a tuple `(subscriber_id, log_id, message)`.
Rules:
- Process logs in their original order.
- For each due, unsent log, send the message to all subscribers of that log's company, in the order stored in the subscriber list.
- After processing a due log, mark it as `sent = True`.
- If a company has no subscribers, the log is still considered processed and must still be marked as sent.
- Return the generated deliveries and the updated logs.
- Do not rely on mutating the caller's input; return the updated state explicitly.
Constraints
- 0 <= number of companies <= 10^4
- 0 <= number of logs <= 10^4
- The total number of subscriber IDs across all companies is <= 10^5
- 0 <= scheduled_at, current_time <= 10^9
- Each `log_id` is unique
- Subscriber IDs within one company's list are distinct