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Zipline·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

45-minute session at Zipline for a software engineer role, basically a code review where they handed me a 1D filter implementation and asked me to tear it apart. Not your typical coding round.

Questions Asked (1)

Q1

Given a 1D filter implementation, identify and explain the deficiencies or bugs in the code.

Root Cause AnalysisTechnical Trade-offsAlgorithms & Data Structures
Author's notes

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AI HintsAI Generated

Suggested Approach

Start by clarifying the filter's intended behavior and constraints (e.g., real-time, embedded, safety-critical). Then systematically trace the code for correctness, edge cases, and performance issues, explaining the impact of each deficiency. Prioritize bugs that could cause incorrect output or system failures.

Pro tip: Demonstrate a testing mindset: mention how you would write unit tests to expose each bug, and discuss trade-offs between fixing for correctness versus performance. This shows you think beyond just spotting errors.

1. Clarify Requirements and Context

Ask about the filter's purpose, input/output expectations, and constraints (e.g., memory, latency, numerical precision). This ensures you evaluate the code against the right criteria.

2. Review for Correctness Bugs

Check for off-by-one errors, incorrect indexing, missing boundary handling, and improper initialization. Verify the filter equation is implemented as intended.

3. Analyze Edge Cases and Robustness

Consider empty input, single-element input, extreme values, and non-finite numbers. Identify how the code handles these and whether it could crash or produce wrong results.

4. Evaluate Performance and Efficiency

Look for unnecessary computations, poor memory access patterns, or lack of optimization (e.g., loop unrolling, SIMD). Discuss trade-offs between readability and speed.

5. Propose Fixes and Tests

Suggest concrete corrections and how to validate them with unit tests. Mention any refactoring for clarity or maintainability.

Key Points to Mention

  • Off-by-one errors in loop bounds or buffer indexing
  • Missing or incorrect handling of boundary conditions (e.g., first/last samples)
  • Potential integer overflow or precision loss in fixed-point/float arithmetic
  • Lack of input validation (e.g., null pointers, zero-length input)
  • Performance bottlenecks such as redundant calculations or cache-unfriendly access
  • Importance of unit tests and property-based testing for filter correctness

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