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cortex·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Two practical coding tasks for a Software Engineer role at Cortex. Nothing too exotic, but the follow-up discussion on the first one pushed into real engineering territory, and the org chart problem had enough edge cases to keep things interesting.

Questions Asked (3)

Q1

Make a GET request to an HTTP endpoint that returns a JSON list of transit stops, then print each stop's name and description on one line.

API & IntegrationsTechnical Trade-offs
Author's notes

Pretty straightforward fetch-and-parse.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements and constraints, then outline a solution using an HTTP client library, handling the JSON response, and iterating over the stops. Emphasize error handling, code readability, and potential edge cases. Finally, discuss trade-offs and possible improvements.

Pro tip: Mention that you would use a timeout and retry logic for robustness, and consider pagination if the API returns a large list. This shows you think about production readiness beyond the happy path.

1. Clarify Requirements

Ask about the endpoint URL, authentication, expected response format, and any constraints like rate limits or pagination. Confirm the output format (one line per stop with name and description).

2. Choose Tools and Libraries

Select an HTTP client library (e.g., requests in Python, axios in JavaScript) and a JSON parser. Justify your choice based on simplicity, error handling, and async support if needed.

3. Implement the Request and Parsing

Write code to make the GET request, check the status code, parse the JSON response, and extract the list of stops. Handle potential errors like network failures or invalid JSON.

4. Iterate and Print

Loop through each stop, extract the name and description fields, and print them on one line. Consider formatting (e.g., separator) and handle missing fields gracefully.

5. Discuss Edge Cases and Improvements

Mention handling empty lists, pagination, rate limiting, timeouts, and logging. Suggest improvements like using async requests or adding unit tests.

Key Points to Mention

  • HTTP client library selection and justification
  • Error handling for network issues, non-200 status codes, and malformed JSON
  • JSON parsing and data extraction, including handling missing fields
  • Output formatting: one line per stop with name and description
  • Edge cases: empty response, pagination, rate limiting, timeouts
  • Code readability, maintainability, and potential for testing

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

Q2

Following the API task: what would you change to make this production-ready? Think about error handling, retries, timeouts, logging, schema changes, pagination, and testing.

API & IntegrationsTechnical Trade-offsSystem Design
Author's notes

This is where it got more interesting.

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AI HintsAI Generated

Suggested Approach

Acknowledge the working prototype, then systematically walk through production concerns: reliability (error handling, retries, timeouts), observability (logging, metrics), scalability (pagination, rate limiting), and maintainability (schema evolution, testing). Prioritize changes by impact and risk, and tie each to real-world failure modes.

Pro tip: Frame improvements in terms of user impact and operational cost—e.g., 'Without idempotent retries, a network blip could double-charge a customer.' This shows you think beyond code to business consequences.

1. Harden error handling and retries

Define clear error taxonomy (client vs. server, transient vs. permanent) and implement retries with exponential backoff and jitter for transient failures. Ensure idempotency keys for non-idempotent operations to avoid duplicate side effects.

2. Add timeouts and circuit breakers

Set aggressive but reasonable timeouts on all external calls and use circuit breakers to fail fast when dependencies are degraded. This prevents cascading failures and resource exhaustion.

3. Implement structured logging and monitoring

Replace ad-hoc logs with structured, contextual logging (request IDs, user IDs, latency) and emit metrics for key operations. Set up alerts on error rates and latency percentiles.

4. Design for scalability and evolution

Add pagination (cursor-based preferred) to list endpoints, enforce rate limiting, and plan for schema changes using versioning or backward-compatible fields. Document API contracts and deprecation policies.

5. Build a comprehensive test suite

Cover unit tests for logic, integration tests for API contracts, and end-to-end tests for critical flows. Include chaos testing for failure scenarios and contract tests to catch breaking changes.

Key Points to Mention

  • Idempotency and retry safety: use idempotency keys and ensure retries don't cause duplicate operations.
  • Timeouts and circuit breakers: prevent cascading failures and improve system resilience.
  • Structured logging with correlation IDs: enable tracing and debugging across services.
  • Cursor-based pagination: more stable and efficient than offset-based for large datasets.
  • Schema versioning and backward compatibility: allow safe evolution without breaking clients.
  • Testing pyramid: unit, integration, contract, and end-to-end tests, plus failure injection.

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

Q3

Given a CSV of employees with their manager's name, print the org chart with each level indented by two spaces, and direct reports sorted alphabetically under each manager.

Algorithms & Data StructuresData Modeling
Author's notes

The core idea clicked fast: build a children map keyed by manager name, find the root (empty manager field), then do a DFS printing with a depth counter.

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AI HintsAI Generated

Suggested Approach

Clarify the CSV format and edge cases, then build a tree from the employee-manager relationships. Use a depth-first traversal to print each node with indentation, sorting children alphabetically at each level.

Pro tip: Mention that you'd handle multiple roots (e.g., CEO and contractors) and cycles gracefully, and that you'd use a stack or recursion with a visited set to avoid infinite loops.

1. Clarify requirements and edge cases

Ask about CSV columns, handling of missing managers, multiple roots, cycles, and whether the output should include the root at zero indentation.

2. Parse and build the tree

Read the CSV, create a node for each employee, and link each node to its manager. Use a dictionary for O(1) lookups and store children in a list.

3. Sort children alphabetically

For each node, sort its list of direct reports by name to ensure the required alphabetical order at every level.

4. Traverse and print with indentation

Perform a depth-first traversal starting from the root(s), printing each employee's name with indentation proportional to depth (two spaces per level).

5. Test and discuss complexity

Walk through a small example, verify edge cases, and state time complexity O(N log N) due to sorting and space O(N) for the tree.

Key Points to Mention

  • Building a tree from parent-child relationships using a hash map for efficient lookup
  • Handling multiple roots and cycles with a visited set or by detecting back-edges
  • Sorting children alphabetically at each node, considering case sensitivity and locale
  • Using depth-first search (recursive or iterative) for traversal and indentation
  • Time and space complexity analysis: O(N log N) time, O(N) space
  • Edge cases: empty CSV, single employee, missing manager, duplicate names

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