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Amazon·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Amazon SWE coding round with a Python data processing problem. Pretty standard algorithmic stuff but they threw in the complexity analysis requirement which I wasn't expecting to spend much time on.

Questions Asked (1)

Q1

Given a 2D list of integers, compute the sum of squares for each sublist and return the results as a flat list. You cannot use built-in aggregation functions like sum. Also provide time and space complexity analysis.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

The core logic wasn't bad, nested loops to accumulate squares manually.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem constraints and edge cases, then walk through a manual example to demonstrate understanding. Implement a solution using nested loops to compute the sum of squares for each sublist without built-in aggregation, and finally analyze time and space complexity.

Pro tip: Explicitly state that you're avoiding built-in sum to comply with the constraint, and mention that you're considering potential integer overflow, showing attention to detail and robustness.

1. Clarify requirements and edge cases

Ask about input size, possible empty sublists, negative numbers, and whether the output should preserve order. Confirm that built-in sum is prohibited.

2. Outline approach

Explain that you'll iterate through each sublist, compute the sum of squares using a loop, and append the result to a flat list.

3. Implement solution

Write code with nested loops: outer loop over sublists, inner loop over elements, accumulating squares in a variable, then appending to result list.

4. Analyze complexity

State that time complexity is O(N) where N is total number of elements, and space complexity is O(M) for the output list where M is number of sublists (excluding input).

5. Test with examples

Walk through a sample input, including edge cases like empty sublists or negative numbers, to verify correctness.

Key Points to Mention

  • Avoiding built-in sum by using explicit loops
  • Handling edge cases such as empty sublists and negative integers
  • Time complexity O(N) where N is total elements
  • Space complexity O(M) for output, O(1) extra space
  • Potential integer overflow and use of appropriate data types
  • Preserving order of sublists in the output

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