Amazon·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jul 2026

Summary

Amazon SWE coding round with a classic array problem. Nothing too wild but the O(1) space constraint is where people trip up if they haven't seen it before.

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 cannot use division, and you must do it in O(1) extra space (not counting the output array).

Algorithms & Data Structures

Author's notes

The no-division rule is obvious enough but the O(1) space thing is what actually bites you.

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AI HintsAI Generated

Suggested Approach

Use two passes: first compute prefix products and store them in the output array, then traverse from right to left while maintaining a running suffix product and multiply it into each position. This achieves O(n) time and O(1) extra space (output array not counted).

Pro tip: Clarify upfront that the output array is not considered extra space, and mention edge cases like zeros and single-element arrays to show thoroughness.

1. Clarify constraints and edge cases

Confirm that the output array doesn't count towards space complexity, and discuss handling of zeros, negative numbers, and arrays of length 0 or 1.

2. Explain the two-pass approach

Describe how to compute prefix products in the first pass and store them in the output array, then compute suffix products on the fly in the second pass.

3. Walk through an example

Use a small array like [1,2,3,4] to demonstrate the prefix and suffix products step by step, showing how the final output is built.

4. Analyze complexity

State that time complexity is O(n) and extra space is O(1) (excluding the output array), and explain why division is avoided.

5. Discuss edge cases and alternatives

Mention how zeros are handled naturally, and briefly note that a division-based approach would fail with zeros and is disallowed.

Key Points to Mention

Two-pass algorithm: left-to-right for prefix products, right-to-left for suffix products.
O(n) time complexity and O(1) extra space (output array excluded).
Handling of zeros: if there are two or more zeros, all outputs are zero; if one zero, only that position gets the product of non-zeros.
Avoiding division as required, and why division would be problematic with zeros.
In-place modification of the output array to store intermediate results.
Edge cases: empty array, single element, negative numbers.

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