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Google·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Google SWE interview with a sorting algorithm deep dive. They went way beyond just asking you to write the code, wanted the full complexity analysis and a real conversation about tradeoffs. Left feeling like I could've been sharper on the worst-case discussion.

Questions Asked (1)

Q1

Implement bucket sort and walk through the algorithm, its time and space complexity, stability, and when you'd actually choose it over a comparison-based sort.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

I got the basic steps down fine: create K buckets, distribute elements, sort each bucket, concatenate.

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AI HintsAI Generated

Suggested Approach

Start by clearly defining the problem and the assumptions (e.g., uniformly distributed input, range of values). Then implement bucket sort step-by-step, explaining each phase and its complexity. Finally, compare it with comparison-based sorts, highlighting trade-offs and practical scenarios where bucket sort excels.

Pro tip: Emphasize that bucket sort's performance hinges on the distribution of input; mention that in practice, you'd often use a hybrid approach (e.g., insertion sort within buckets) to handle small buckets efficiently. Also, note that bucket sort is stable if the underlying sort is stable and buckets are processed in order.

1. Clarify assumptions and constraints

Ask about the input distribution, range, and whether the data is uniformly distributed. Confirm if the sort needs to be stable and if extra space is acceptable.

2. Explain the algorithm

Describe the steps: create buckets, distribute elements into buckets based on a mapping function, sort each bucket (often with insertion sort), and concatenate buckets in order.

3. Analyze complexity

State average-case time complexity O(n + k) for n elements and k buckets, assuming uniform distribution. Mention worst-case O(n^2) when all elements land in one bucket. Space complexity is O(n + k).

4. Discuss stability

Explain that bucket sort is stable if the sorting algorithm used within buckets is stable and elements are appended in order. Otherwise, it may not be stable.

5. Compare with comparison sorts and when to use

Contrast with O(n log n) comparison sorts like quicksort or mergesort. Highlight that bucket sort can be faster for uniformly distributed data but requires knowledge of the range and extra space. Mention use cases like sorting floating-point numbers in [0,1) or external sorting.

Key Points to Mention

  • Bucket sort is a distribution sort that assumes input is uniformly distributed over a range.
  • Time complexity: average O(n + k), worst O(n^2) if distribution is skewed.
  • Space complexity: O(n + k) for buckets and auxiliary arrays.
  • Stability depends on the sorting algorithm used within buckets; using insertion sort makes it stable.
  • Choose bucket sort when input is uniformly distributed and range is known, and when O(n) average performance is desired.
  • Comparison-based sorts have O(n log n) lower bound, but bucket sort can beat that by not comparing elements directly.

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