Anthropic·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say

Jul 2026Remote

Summary

Interviewed for a software engineer role at Anthropic and got hit with a profiler trace parsing problem that looked deceptively manageable until you start thinking about all the edge cases. The core algorithm part was fine but the follow-up about malformed input and infinite loops is where things got interesting.

Questions Asked (1)

Given a time-ordered profiler event log with START and END events for a single-threaded program, design an algorithm to compute inclusive and exclusive running times for each function, return the slowest function by exclusive time, and handle edge cases like recursion, cycles, missing END events, and functions that never return.

Algorithms & Data StructuresSystem DesignTechnical Trade-offs

Author's notes

I went straight to the stack-based approach: push on START, pop on END, accumulate exclusive time by subtracting child durations.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Use a stack to track active function calls, processing START and END events in order. Maintain a map of function names to inclusive and exclusive times, and handle edge cases by validating event sequences and using a default duration for missing END events.

Pro tip: Explicitly discuss trade-offs between using a stack-based single-pass approach versus other methods, and mention how to handle recursion by treating each invocation separately. Also, clarify assumptions about timestamp resolution and event ordering.

1. Clarify requirements and assumptions

Confirm that the log is well-formed except for specified edge cases, and define how to handle missing END events (e.g., assume they run until the last timestamp).

2. Design data structures

Use a stack to track active function calls, and a hash map to accumulate inclusive and exclusive times per function.

3. Process events in order

For each START event, push onto stack and record start time; for each END event, pop the stack, compute duration, update inclusive time, and subtract from parent's exclusive time.

4. Handle edge cases

Detect mismatched END events (ignore or log), handle recursion by treating each call independently, and for missing END events, assign duration from start to last timestamp.

5. Compute and return results

After processing, find the function with the maximum exclusive time and return it along with inclusive/exclusive times.

Key Points to Mention

Use of stack to manage nested calls and recursion
Separate tracking of inclusive and exclusive times
Handling missing END events by assuming they run until the end of the log
Ignoring or logging mismatched END events (e.g., END without START)
Time complexity O(n) and space complexity O(n) where n is number of events
Edge case: functions that never return (infinite loops) - treat as running until last timestamp

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.