Find the First Unique Log
Company: Uber
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Onsite
You are given a list of log entries in the order they were produced. Each log entry can be treated as a string.
Return the first log entry that appears exactly once in the entire list. If no such log entry exists, return `null` or an equivalent empty result.
Example:
Input: `["login", "click", "logout", "login", "purchase", "click"]`
Output: `"logout"`
Follow-up: How would your approach change if the input contains about 10 million log entries? Discuss time complexity, memory usage, and any practical considerations for large-scale processing.
Quick Answer: This question evaluates a candidate's ability to analyze and implement efficient data-processing and frequency-detection strategies on ordered string sequences, with attention to time and memory complexity.
Given log entries in production order, return the first entry that appears exactly once in the whole list. Return None when every entry repeats.
Constraints
- logs length can be large
- log entries are strings
Examples
Input: (['login', 'click', 'logout', 'login', 'purchase', 'click'],)
Expected Output: 'logout'
Input: (['a', 'b', 'a', 'b'],)
Expected Output: None
Input: ([],)
Expected Output: None
Input: (['same', 'unique', 'same', 'later'],)
Expected Output: 'unique'
Hints
- Count frequencies first, then scan in original order.