Meta·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026

Summary

Meta coding round for a Software Engineer role. One problem, but it had enough layers to keep me busy for the whole session.

Questions Asked (1)

Given an integer array, return a new array where each element is the product of all other elements in the original array. You must do this in O(n) time, without division, and using only constant extra space beyond the output array. Also discuss how you'd handle zeros, negative numbers, and overflow, and write unit tests.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I knew the prefix/suffix product trick going in, so the core algorithm wasn't the hard part.

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AI HintsAI Generated

Suggested Approach

Use a two-pass prefix-suffix product approach: first compute prefix products in the output array, then traverse from right to left maintaining a running suffix product to multiply into each position. This achieves O(n) time and O(1) extra space (output array not counted). Discuss edge cases like zeros, negatives, and overflow, and outline unit tests covering these scenarios.

Pro tip: Clarify with the interviewer whether the output array counts towards space complexity; typically it does not, so the solution is considered O(1) extra space. Also, mention that handling zeros requires special care because a single zero makes all other products zero except at the zero's index, and multiple zeros make all products zero.

1. Clarify requirements and constraints

Confirm that the output array does not count towards extra space, and discuss the implications of no division, O(n) time, and constant extra space. Ask about input size and potential overflow handling.

2. Design the two-pass prefix-suffix algorithm

Explain that you will first compute prefix products (product of all elements before index i) and store them in the output array. Then traverse from right to left, maintaining a running suffix product (product of all elements after index i) and multiply it with the prefix product at each index.

3. Handle edge cases: zeros, negatives, overflow

Discuss how zeros affect the product: if there is one zero, only the element at the zero's index gets a non-zero product; if multiple zeros, all products are zero. Negative numbers are handled naturally by multiplication. For overflow, consider using a larger data type or discuss with the interviewer.

4. Write unit tests

Outline test cases: empty array, single element, array with one zero, array with multiple zeros, array with negative numbers, and large numbers to test overflow. Verify that the output matches expected results.

5. Analyze complexity and trade-offs

State that time complexity is O(n) and extra space is O(1) (excluding output). Mention that the two-pass approach is optimal and avoids division, which is a common pitfall.

Key Points to Mention

Two-pass prefix and suffix product approach
O(n) time complexity and O(1) extra space (output array excluded)
Handling zeros: one zero vs multiple zeros
Negative numbers are handled naturally
Overflow considerations and potential use of larger data types
Unit tests covering edge cases: empty, single element, zeros, negatives, large numbers

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