Find the First Unique IP
Company: Uber
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Technical Screen
You are processing a chronological stream of server hit records. Each record contains an IP address as a string.
Design and implement a component that supports the following operations:
- `recordHit(ip: string)`: Add a new server hit from `ip`.
- `getFirstUniqueIp() -> string | null`: Return the earliest IP address in the stream that has appeared exactly once so far. If no such IP exists, return `null`.
Example:
```text
recordHit("10.0.0.1")
recordHit("10.0.0.2")
recordHit("10.0.0.1")
getFirstUniqueIp() -> "10.0.0.2"
recordHit("10.0.0.2")
getFirstUniqueIp() -> null
recordHit("10.0.0.3")
getFirstUniqueIp() -> "10.0.0.3"
```
Follow-up: How would you scale the solution if the server receives millions or billions of hit records? Discuss memory usage, throughput, and any trade-offs if exact results are required versus approximate results.
Quick Answer: This question evaluates proficiency with streaming data handling, stateful data structures, and algorithmic design for identifying unique elements in chronological event streams, and is categorized under Coding & Algorithms.