Pinterest·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Pinterest coding screen, one question, combinatorics flavored. Pretty straightforward but the kind of thing you want to have seen before so you don't fumble the implementation.

Questions Asked (1)

Given a dictionary where each key maps to a list of possible values, generate all combinations as a list of dictionaries, one per combination.

Algorithms & Data Structures

Author's notes

Classic cartesian product problem.

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AI HintsAI Generated

Suggested Approach

Use a recursive backtracking approach to build combinations incrementally, iterating through each key's list and recursing to the next key. At the base case (all keys processed), add a copy of the current combination to the result. Alternatively, use an iterative approach with a queue or reduce operation to generate combinations.

Pro tip: Clarify edge cases upfront, such as empty dictionary or empty value lists, and discuss time/space complexity (O(N * M) where N is number of combinations and M is number of keys). Mention that you'd use deep copies to avoid reference issues.

1. Clarify requirements and edge cases

Ask about input constraints, expected output format, and how to handle empty dictionaries or empty value lists. Confirm whether the order of combinations matters.

2. Choose an approach

Decide between recursive backtracking (simpler, more readable) or iterative (e.g., using reduce or BFS). Explain the trade-offs in terms of code clarity and performance.

3. Implement the solution

Write clean code with meaningful variable names. For recursion, define a helper function that takes the current index and current combination, and at each step iterates over the values for the current key.

4. Test with examples

Walk through a small example (e.g., {'A': [1,2], 'B': [3,4]}) to verify correctness. Also test edge cases like empty dictionary or empty lists.

5. Analyze complexity and optimize

Discuss time and space complexity. If needed, suggest optimizations like pruning or using generators for large inputs.

Key Points to Mention

Recursive backtracking with base case when all keys are processed
Using deep copies of the current combination to avoid reference issues
Handling edge cases: empty dictionary, empty value lists, single key
Time complexity: O(N * M) where N is number of combinations and M is number of keys
Space complexity: O(N * M) for storing all combinations
Alternative iterative approach using reduce or BFS

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