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Upstart·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Coding screen for a software engineer role at Upstart. One question, pretty focused on list manipulation and knowing your streams API well enough to not fumble it.

Questions Asked (1)

Q1

Given a list of integers, filter out the odd numbers and return the even numbers in reverse order.

Algorithms & Data Structures
Author's notes

Seemed simple at first and I went straight to a streams solution.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem and any constraints (e.g., input size, memory limits, whether the input can be modified). Then discuss a straightforward solution using a single pass to collect evens and reverse them, and analyze its time and space complexity. If appropriate, mention alternative approaches like in-place reversal or using two pointers, and compare trade-offs.

Pro tip: Demonstrate awareness of edge cases and production concerns: ask about input size to decide between in-memory and streaming approaches, and mention that in a real system you'd consider readability, testability, and whether the function should mutate the input.

1. Clarify requirements and constraints

Ask about input size, data types, whether the input list can be modified, and expected output format. Confirm if the result should be a new list or if in-place modification is acceptable.

2. Outline a simple approach

Propose iterating through the list once to collect even numbers into a new list, then reversing that list. State the time complexity O(n) and space complexity O(k) where k is the number of evens.

3. Discuss alternative approaches and trade-offs

Mention that you could reverse the original list first and then filter, or use two pointers to filter in-place if mutation is allowed. Compare readability, memory usage, and performance.

4. Handle edge cases and test

Walk through edge cases: empty list, all odds, all evens, single element. Suggest writing unit tests to verify correctness.

5. Write clean, efficient code

Implement the chosen approach with clear variable names and comments. If time permits, optimize for space by using in-place reversal when possible.

Key Points to Mention

  • Time and space complexity analysis (O(n) time, O(k) space for the simple approach).
  • Edge cases: empty list, no evens, all evens, large input.
  • In-place vs. out-of-place trade-offs (memory vs. mutability).
  • Readability and maintainability of code (e.g., using list comprehensions in Python).
  • Potential follow-up: how to handle streaming data or very large inputs that don't fit in memory.
  • Testing strategy: unit tests for correctness and performance tests for large inputs.

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