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Anthropic·Software Engineer·Technical Phone Screen·Senior

Senior
Jun 2026

Summary

Technical phone screen for a software engineering role at Anthropic. One meaty parsing question that went pretty deep into tree construction and edge case handling. Not a vibe check, they wanted actual working code.

Questions Asked (1)

Q1

Given a multi-line stack trace string from a single thread, design and implement a parser that extracts frames in order (most recent to oldest), reconstructs the call hierarchy as a tree, identifies the deepest frame tied to the thrown exception, and correctly handles nested 'Caused by:' sections, abbreviated '... N more' lines, and malformed or missing lines. Walk through your data structures, time/space complexity, and provide working code.

Algorithms & Data StructuresSystem DesignTechnical Trade-offs
Author's notes

This one took me a second to even parse the problem statement, which is ironic.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the stack trace format and edge cases, then outline a line-by-line parsing strategy using a stack to build the call tree. Explain how to handle 'Caused by:' and '... N more' by maintaining separate exception contexts and frame counts, and finally analyze complexity and provide clean, tested code.

Pro tip: Mention that '... N more' lines indicate omitted frames that are common with the enclosing exception's stack, so you can merge them by skipping N frames from the parent exception's stack—this shows deep understanding of JVM stack trace semantics.

1. Clarify requirements and edge cases

Ask about the exact stack trace format (e.g., Java), expected handling of malformed lines, and whether to include suppressed exceptions. Confirm that 'deepest frame tied to the thrown exception' means the frame where the exception was thrown (top of the stack for that exception).

2. Design data structures

Use a Frame class (class name, method, file, line) and an ExceptionNode class (exception type, message, list of frames, list of caused-by exceptions). Maintain a stack of ExceptionNodes to handle nested 'Caused by:' sections, and a map from exception to its frame list for merging '... N more'.

3. Parse line by line

Iterate through lines: detect exception headers (e.g., 'Exception in thread...' or 'Caused by:'), parse frame lines with regex, handle '... N more' by recording the count, and ignore malformed lines. Push/pop ExceptionNodes as you encounter 'Caused by:' to build the tree.

4. Reconstruct hierarchy and handle '... N more'

After parsing, for each '... N more', find the parent exception's frame list and skip N frames from the end to merge the omitted frames. Build the final tree with the root exception and its caused-by chain.

5. Analyze complexity and code

Time complexity O(L) where L is number of lines, space O(F) for F frames. Write clean code with helper methods, and test with sample stack traces including nested causes and malformed lines.

Key Points to Mention

  • Use a stack to manage nested 'Caused by:' exceptions and build the tree.
  • Parse frames with a regex that captures class, method, file, and line number.
  • Handle '... N more' by merging with the parent exception's frame list, skipping N frames.
  • Identify the deepest frame as the top frame of the exception's own stack (where it was thrown).
  • Ignore malformed lines gracefully and continue parsing.
  • Time complexity O(L) and space O(F) where L is lines and F is frames.

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