Jump Trading·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026

Summary

Jump Trading systems interview, probably for a software engineering role. One meaty question about file comparison that spiraled into a bunch of follow-ups on streaming and directories. Felt like a design question dressed up as a coding question.

Questions Asked (1)

Given a source file and a destination file, compare their contents and report whether they differ. If they do, describe what changed. How would you handle large files, line-based vs byte-based comparison, and extending this to a whole directory?

System DesignTechnical Trade-offsAlgorithms & Data Structures

Author's notes

Started with the obvious line-by-line diff approach and they immediately asked what happens when the file is 10GB.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements: what constitutes a difference (line vs byte), expected file sizes, and whether the comparison is for equality or detailed diff. Then propose a streaming approach that handles large files efficiently, and discuss trade-offs between line-based and byte-based comparison. Finally, outline how to extend the solution to directories, including recursion and handling of binary files.

Pro tip: Mention that for large files, you should avoid loading entire files into memory; instead, use buffered streaming and compare chunks. Also, consider using hashing for quick inequality checks, but be aware of hash collisions and the need for a fallback to exact comparison.

1. Clarify Requirements

Ask about the definition of 'difference', expected file sizes, performance constraints, and whether the output should be a boolean or a detailed diff. This ensures you address the actual problem.

2. Choose Comparison Mode

Decide between line-based and byte-based comparison based on the file type and requirements. Line-based is suitable for text files and provides human-readable diffs; byte-based is necessary for binary files and exact equality checks.

3. Design for Large Files

Propose a streaming algorithm that reads files in chunks (e.g., using buffered I/O) to keep memory usage constant. For line-based comparison, use a line-by-line diff algorithm like Myers; for byte-based, compare chunks and handle differing chunk sizes.

4. Extend to Directories

Outline a recursive directory walk that compares corresponding files, handles added/removed files, and optionally skips binary files or uses a different comparison for them. Consider parallelization for performance.

5. Discuss Trade-offs and Optimizations

Mention trade-offs: line-based may miss whitespace differences if normalized; byte-based is exact but not human-readable. Optimizations: use file size check first, then hash, then exact comparison; use memory-mapped files for large files if appropriate.

Key Points to Mention

Streaming/buffered I/O to handle large files without loading into memory
Line-based vs byte-based comparison: use cases and trade-offs
Diff algorithms (e.g., Myers diff) for line-based comparison
Hashing (e.g., MD5, SHA) for quick inequality checks, with collision caveats
Directory traversal: recursion, handling added/removed files, and binary file detection
Performance considerations: parallelization, memory-mapped files, and early exit on size mismatch

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