Find the Most Frequent Log Call
Company: Roblox
Role: Machine Learning Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Technical Screen
You are given a sequence of application log entries. Each entry contains the name of a function or API call made by the system. Write a function that returns the call that appears most frequently in the logs, along with its frequency.
Example:
- Input: ["login", "search", "login", "checkout", "search", "login"]
- Output: ("login", 3)
Follow-up discussion can include how to handle ties, how to return the top-k most frequent calls, and how to process logs in a streaming or large-scale setting.
Quick Answer: This question evaluates a candidate's ability to perform frequency analysis on sequences, demonstrating competency with data structures for counting occurrences and with algorithmic time and space complexity considerations.
You are given a sequence of application log entries as a list of strings, where each entry is the name of a function or API call made by the system. Return the call that appears most frequently in the logs, along with its frequency, as a pair `(call, frequency)`.
If multiple calls are tied for the highest frequency, return the one that first appears earliest in the log sequence. If the log is empty, return `("", 0)`.
Example:
- Input: ["login", "search", "login", "checkout", "search", "login"]
- Output: ("login", 3)
Follow-up directions you could discuss in an interview: how to handle ties, how to return the top-k most frequent calls, and how to process logs in a streaming or large-scale (multi-machine) setting.
Constraints
- 0 <= len(logs) <= 10^6
- Each log entry is a non-empty string of an API/function call name.
- Ties are broken by earliest first appearance in the log sequence.
- Return ("", 0) for an empty log.
Examples
Input: (["login", "search", "login", "checkout", "search", "login"],)
Expected Output: ("login", 3)
Explanation: "login" appears 3 times, more than "search" (2) and "checkout" (1).
Input: (["a", "b", "a", "b"],)
Expected Output: ("a", 2)
Explanation: "a" and "b" both appear twice; "a" appears first, so it wins the tie.
Hints
- Use a hash map to count occurrences of each call in a single pass.
- Track each call's first-appearance index so you can break frequency ties deterministically.
- For the top-k follow-up, a heap of size k or bucket sort by frequency avoids fully sorting all distinct calls; for streaming/large-scale, think Count-Min Sketch or a map-reduce word-count.