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Meta·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jul 2026

Summary

Interviewed for a data engineer role at Meta, got a sorting algorithms question that felt more CS fundamentals than data engineering but I guess they want to know you know the basics.

Questions Asked (1)

Q1

Which sorting algorithms are based on a divide and conquer approach?

Algorithms & Data Structures
Author's notes

Merge sort and quicksort, pretty much.

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AI HintsAI Generated

Suggested Approach

Start by clearly defining the divide-and-conquer paradigm: divide the problem into subproblems, solve them recursively, and combine the results. Then name the primary sorting algorithms that follow this approach—Merge Sort and Quick Sort—and briefly explain how each applies the paradigm. Optionally, mention others like Heap Sort (which uses a heap but not typically classified as divide-and-conquer) or Timsort (a hybrid), but focus on the core ones.

Pro tip: Demonstrate depth by contrasting Merge Sort's stable, predictable O(n log n) performance with Quick Sort's in-place partitioning and average-case efficiency, and note that Quick Sort's worst-case O(n^2) can be mitigated with randomized pivots. This shows you understand trade-offs beyond just naming algorithms.

1. Define Divide and Conquer

Briefly explain the paradigm: break the problem into smaller subproblems, solve them recursively, and combine the solutions.

2. Identify Merge Sort

Describe how Merge Sort divides the array into halves, recursively sorts each half, and merges them. Mention its stable O(n log n) time complexity.

3. Identify Quick Sort

Explain how Quick Sort selects a pivot, partitions the array, and recursively sorts the sub-arrays. Note its average O(n log n) and worst-case O(n^2) performance.

4. Mention Other Algorithms (Optional)

If relevant, mention that algorithms like Timsort (hybrid) or Strand Sort also use divide-and-conquer principles, but clarify that Merge Sort and Quick Sort are the classic examples.

5. Summarize and Contrast

Conclude by summarizing that both Merge Sort and Quick Sort are divide-and-conquer, and highlight key differences in stability, in-place sorting, and performance guarantees.

Key Points to Mention

  • Divide-and-conquer paradigm: divide, conquer, combine.
  • Merge Sort: stable, O(n log n) worst-case, not in-place.
  • Quick Sort: in-place, average O(n log n), worst-case O(n^2), not stable.
  • Recursive structure of both algorithms.
  • Partitioning step in Quick Sort and merging step in Merge Sort.
  • Potential optimizations: randomized pivot for Quick Sort, hybrid approaches like Timsort.

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