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Decagon·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026Remote

Summary

Phone screen for a software engineer role at Decagon. One coding problem, I talked through everything out loud and got all test cases to pass, but the interviewer seemed completely checked out the whole time. A bit of an odd vibe.

Questions Asked (1)

Q1

Build a recipe shopping cart: given a list of recipes and their ingredients, implement a system to manage and aggregate items for a shopping cart.

Algorithms & Data StructuresAPI & Integrations
Author's notes

Kept narrating my thinking out loud the whole time, which I think actually helped me stay on track.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements: input format, whether recipes can be added/removed, and desired output (aggregated list or map). Then design a data model with Recipe and Ingredient classes, and implement a ShoppingCart that aggregates quantities by ingredient name, handling units and merging duplicates. Discuss trade-offs between simple map-based aggregation and more complex unit conversion.

Pro tip: Proactively ask about unit conversions and duplicate ingredients with different units—this shows you think about real-world edge cases and data integrity. Also, mention that you'd write unit tests for aggregation logic to ensure correctness.

1. Clarify Requirements

Ask about input format (list of recipes with ingredients and quantities), whether recipes can be added/removed dynamically, and expected output (e.g., aggregated list or map). Confirm if unit conversion is needed.

2. Design Data Model

Define classes/structs for Ingredient (name, quantity, unit) and Recipe (name, list of ingredients). Consider using a map or dictionary for efficient aggregation.

3. Implement Aggregation Logic

Iterate through selected recipes, accumulate quantities per ingredient name. Handle unit consistency: either normalize units or group by (name, unit) and convert if possible.

4. Handle Edge Cases

Address duplicate ingredients with different units, zero quantities, and empty recipes. Decide on behavior for incompatible units (e.g., throw error or keep separate).

5. Test and Optimize

Write unit tests for aggregation, including edge cases. Discuss time/space complexity (O(n) where n is total ingredients) and potential optimizations like caching.

Key Points to Mention

  • Use a hash map (dictionary) to aggregate quantities by ingredient name for O(1) average lookup.
  • Consider unit conversion: either normalize to a base unit or group by (name, unit) and convert when possible.
  • Define clear interfaces: methods like addRecipe, removeRecipe, getShoppingList.
  • Handle edge cases: duplicate ingredients, different units, zero quantities, empty input.
  • Discuss trade-offs: simplicity vs. flexibility (e.g., supporting unit conversion adds complexity).
  • Mention testing: unit tests for aggregation logic and edge cases.

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