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Stripe·Software Engineer·Take-home Assignment·Intermediate

Intermediate
Jun 2026

Summary

Stripe gave me a take-home coding task split into four sub-tasks, all centered around working with a map API and some geometric/landmark data. Pretty hands-on, no live coding pressure, which I appreciated.

Questions Asked (4)

Q1

Parse a JSON file containing geometric point/coordinate data and work with it programmatically.

API & IntegrationsAlgorithms & Data Structures
Author's notes

Straightforward file I/O stuff.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the JSON schema and expected operations (e.g., parsing, validation, distance calculations). Then outline a robust parsing strategy with error handling, followed by efficient algorithms for the required geometric computations. Emphasize code quality, edge cases, and performance considerations.

Pro tip: Demonstrate awareness of real-world data issues like malformed JSON, missing coordinates, or coordinate system variations, and mention how you'd handle them gracefully. Also, briefly discuss time/space complexity of your chosen algorithms to show engineering maturity.

1. Clarify Requirements

Ask about the JSON structure, expected operations (e.g., find nearest point, compute convex hull), input size, and performance constraints. Confirm the coordinate system (2D/3D) and data types.

2. Design Parsing & Validation

Outline a plan to parse JSON using a standard library, validate schema (e.g., required fields, numeric types), and handle errors (malformed JSON, missing data). Consider streaming for large files.

3. Choose Data Structures

Select appropriate in-memory representations (e.g., list of tuples, custom Point class) and any auxiliary structures (e.g., k-d tree for nearest neighbor) based on operations.

4. Implement Algorithms

Describe algorithms for the required geometric operations, focusing on correctness and efficiency. Discuss trade-offs (e.g., brute force vs. spatial indexing).

5. Test & Optimize

Mention testing with edge cases (empty file, single point, collinear points) and performance profiling. Suggest optimizations like lazy parsing or parallel processing if needed.

Key Points to Mention

  • JSON parsing libraries (e.g., json in Python, Jackson in Java) and error handling for malformed input.
  • Validation of coordinate data: ensuring numeric types, required fields, and handling null/missing values.
  • Choice of data structures: arrays vs. objects, and spatial data structures like k-d trees or quadtrees for efficient queries.
  • Algorithm complexity: time and space trade-offs for operations like distance calculation, nearest neighbor, or convex hull.
  • Edge cases: empty datasets, duplicate points, collinear points, and large files requiring streaming.
  • Code quality: modular functions, clear naming, and documentation for maintainability.

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

Q2

Make an API request to fetch a map image based on the parsed coordinates and save it to disk.

API & IntegrationsTechnical Trade-offs
Author's notes

This is where I spent more time than expected.

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AI HintsAI Generated

Suggested Approach

Walk through a robust implementation that fetches a map image from an API using parsed coordinates, handles errors and rate limits, and saves it to disk efficiently. Emphasize production concerns like retries, streaming, and idempotency, and discuss trade-offs between synchronous and asynchronous approaches.

Pro tip: Mention that you would stream the response directly to disk to avoid loading large images into memory, and always set a timeout and validate the content type before saving.

1. Validate and prepare inputs

Ensure the parsed coordinates are valid (latitude/longitude ranges) and construct the API request URL with necessary parameters (e.g., zoom, size, API key).

2. Make the API request with resilience

Use an HTTP client with timeout, retry logic for transient failures, and proper error handling for non-200 responses. Consider rate limiting and backoff.

3. Stream and save the image

Stream the response body directly to a file on disk to avoid memory bloat, and verify the content type is an image before writing.

4. Handle errors and cleanup

On failure, clean up partial files and log errors with context. On success, optionally verify the file integrity (e.g., check size or checksum).

5. Discuss trade-offs and improvements

Talk about synchronous vs asynchronous execution, caching strategies, and how to make the operation idempotent for retries.

Key Points to Mention

  • Use of streaming to avoid loading large images into memory
  • Error handling and retry logic with exponential backoff
  • Setting timeouts and validating content type before saving
  • Idempotency and safe retries (e.g., using a unique filename or checksum)
  • Trade-offs between synchronous and asynchronous processing
  • Security considerations: API key management and input sanitization

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

Q3

Use the API to annotate the coordinate points onto the downloaded map image and draw connecting lines between them.

API & IntegrationsSystem Design
Author's notes

Fun part actually.

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AI HintsAI Generated

Suggested Approach

Clarify the requirements and constraints first, then outline a high-level design that covers fetching the map image, using the API to annotate coordinates, and drawing connecting lines. Discuss key technical decisions such as API selection, coordinate transformation, and rendering approach, and finally address scalability, error handling, and testing.

Pro tip: Demonstrate awareness of real-world constraints like rate limits, coordinate system mismatches, and image resolution by proactively mentioning how you would handle them. Also, tie your solution to Stripe's context by emphasizing reliability, idempotency, and observability.

1. Clarify Requirements and Constraints

Ask questions to understand the exact use case: What map image format? What API? Are coordinates in lat/long or pixels? What scale and performance requirements? This ensures you solve the right problem.

2. Outline High-Level Architecture

Describe the main components: a service to download the map image, an API client to fetch or compute annotations, a coordinate transformation module, and a rendering engine to draw points and lines. Mention how these components interact.

3. Detail Key Technical Decisions

Explain choices such as using a specific mapping API (e.g., Google Maps Static API), converting geographic coordinates to image pixels, and selecting a drawing library (e.g., Pillow, Canvas). Discuss trade-offs like server-side vs. client-side rendering.

4. Address Scalability and Reliability

Cover how to handle large numbers of points, caching, rate limiting, retries, and idempotency. Mention monitoring and logging for observability.

5. Discuss Testing and Edge Cases

Outline unit tests for coordinate transformation, integration tests with mocked APIs, and visual regression tests. Consider edge cases like invalid coordinates, missing map images, and API failures.

Key Points to Mention

  • Coordinate system transformation (e.g., Web Mercator to pixel coordinates)
  • API integration best practices: authentication, rate limiting, error handling
  • Image rendering techniques: drawing points, lines, and labels with anti-aliasing
  • Scalability considerations: batch processing, caching, and asynchronous workflows
  • Idempotency and retry logic for API calls to ensure reliability
  • Observability: logging, metrics, and tracing for debugging and monitoring

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

Q4

Read a second JSON file of landmarks, annotate each one on the map via the API, and for each landmark find and annotate its nearest point from the first dataset.

API & IntegrationsAlgorithms & Data Structures
Author's notes

This was the most involved sub-task.

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AI HintsAI Generated

Suggested Approach

Clarify the input formats, API capabilities, and scale before designing. Then outline a pipeline: read and validate the landmarks file, annotate each landmark via the API, and for each landmark find its nearest point from the first dataset using an efficient spatial search. Finally, annotate those nearest points and handle edge cases like empty datasets or API failures.

Pro tip: Mention that you would batch API calls or use concurrency to avoid rate limits and improve performance, and that you would preprocess the first dataset into a spatial index (e.g., k-d tree) if nearest-neighbor queries are frequent.

1. Clarify requirements and constraints

Ask about the file formats, API rate limits, expected data size, and whether the first dataset is static or dynamic. Confirm the definition of 'nearest' (e.g., Euclidean distance) and how to handle ties or missing data.

2. Read and validate the landmarks file

Parse the second JSON file, validate its structure, and extract landmark coordinates. Handle errors such as malformed JSON or missing fields gracefully.

3. Annotate landmarks via the API

For each landmark, call the API to place an annotation on the map. Consider batching or parallelizing requests to respect rate limits and improve efficiency.

4. Find nearest points from the first dataset

For each landmark, compute the nearest point from the first dataset. Use a spatial index (e.g., k-d tree) for efficiency if the dataset is large; otherwise, a brute-force approach may suffice.

5. Annotate nearest points and handle edge cases

Annotate each nearest point via the API. Handle edge cases such as empty datasets, API errors, and duplicate annotations. Optionally, link each landmark to its nearest point.

Key Points to Mention

  • Input validation and error handling for JSON parsing and API responses
  • API rate limiting, batching, and concurrency to optimize performance
  • Spatial indexing (e.g., k-d tree, ball tree) for efficient nearest-neighbor search
  • Distance metric choice (e.g., Euclidean, Haversine for geographic coordinates)
  • Edge cases: empty datasets, ties, missing coordinates, API failures
  • Scalability considerations: time complexity, memory usage, and potential for parallel processing

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