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Meta·Software Engineer·Onsite - Coding / Algorithms·Intermediate

Intermediate
Jun 2026

Summary

Meta SWE coding round, just the one problem but it was a classic that I probably over-thought in the moment.

Questions Asked (1)

Q1

Given two sorted arrays where the first has enough trailing space to fit the second, merge them in-place so the result stays sorted.

Algorithms & Data Structures
Author's notes

My first instinct was to shift elements forward from the front, which is the wrong move and causes a ton of unnecessary work.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem constraints and edge cases, then propose a solution that merges from the end of the arrays to avoid overwriting elements. Walk through the algorithm step-by-step, analyze its time and space complexity, and test with examples.

Pro tip: Emphasize that merging from the end is the key insight to achieve O(1) extra space and O(m+n) time, and mention that this approach is optimal for in-place merging of sorted arrays.

1. Clarify the problem

Ask questions to confirm the input format, sizes, and assumptions (e.g., arrays are sorted, first array has enough space, no extra space allowed).

2. Discuss approaches

Mention naive approaches (e.g., concatenate and sort) and their drawbacks, then introduce the optimal two-pointer from the end technique.

3. Explain the algorithm

Detail the steps: initialize pointers at the end of both arrays, compare elements, and place the larger one at the end of the first array, moving pointers accordingly.

4. Analyze complexity

State that time complexity is O(m+n) and space complexity is O(1), as no extra space is used.

5. Test with examples

Walk through a simple example and edge cases (e.g., one array empty, all elements of one array smaller) to verify correctness.

Key Points to Mention

  • Merging from the end avoids overwriting elements in the first array.
  • Use three pointers: one for the end of the first array's actual elements, one for the end of the second array, and one for the end of the merged array.
  • Time complexity is O(m+n) and space complexity is O(1).
  • Handle edge cases: empty arrays, all elements of one array smaller than the other.
  • The algorithm is stable and maintains sorted order.
  • This approach is optimal for in-place merging of sorted arrays.

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