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Anthropic·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
May 2026

Summary

Coding round at Anthropic for a software engineer role. One question, stack trace simulation, classic LeetCode territory but still easy to fumble if you're not careful with the off-by-one logic.

Questions Asked (1)

Q1

Given a list of stack-trace events where each event is either a function starting or ending at a given timestamp, compute the exclusive CPU time for each function. When one function calls another, the outer function's time should not count while the inner one is running.

Algorithms & Data Structures
Author's notes

I knew this problem but still tripped up on the bookkeeping.

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AI HintsAI Generated

Suggested Approach

Use a stack to track active function calls, recording start times and accumulating exclusive time when a function ends. When a new function starts, add the elapsed time since the last event to the current top-of-stack function's exclusive time, then push the new function. When a function ends, add the elapsed time to its exclusive time, pop it, and update the timestamp for the parent function.

Pro tip: Clarify whether timestamps are inclusive or exclusive and how nested calls with identical timestamps are handled, as these details can affect the algorithm's correctness. Also, mention that the solution runs in O(n) time and O(d) space, where d is the maximum stack depth.

1. Understand the problem and edge cases

Clarify the input format, timestamp semantics (inclusive/exclusive), and how to handle simultaneous events or multiple calls to the same function. Confirm that exclusive time means time spent in the function excluding time in callees.

2. Design the stack-based algorithm

Use a stack to maintain the call hierarchy. Keep track of the last timestamp processed. For each event, compute the time delta and attribute it to the currently executing function (top of stack).

3. Handle start and end events

On a start event: attribute the time delta to the current top function, then push the new function and update the timestamp. On an end event: attribute the time delta to the function being ended, pop it, and update the timestamp.

4. Aggregate and return results

Maintain a map from function name to exclusive time. After processing all events, return the map or a list of results as required.

5. Analyze complexity and test

State that the algorithm runs in O(n) time and O(d) space, where n is the number of events and d is the maximum stack depth. Walk through a simple example to verify correctness.

Key Points to Mention

  • Use a stack to track the call hierarchy and manage nested function calls.
  • Maintain a variable for the last timestamp to compute time deltas between events.
  • Attribute time deltas to the currently executing function (top of stack) before pushing or popping.
  • Handle start and end events differently: start pushes and attributes to parent, end attributes to child and pops.
  • Aggregate exclusive times in a hash map keyed by function name.
  • Time complexity is O(n) and space complexity is O(d) where d is the maximum call depth.

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