Amazon·Software Engineer·Online Assessment (OA)·Intermediate

IntermediatePrefer not to say

Apr 2026Remote

Summary

Amazon SWE online assessment, pretty standard two-sum style coding problem with a hash table angle. Nothing surprising but the edge cases in the test suite were worth paying attention to.

Questions Asked (1)

Given an integer array and a target value, find two distinct indices where the elements sum to the target. Return the indices in any order, or an empty array if no such pair exists. Aim for better than O(n^2) time.

Algorithms & Data Structures

Author's notes

Classic two-sum, you'd think it's autopilot but the edge cases tripped me up a bit.

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AI HintsAI Generated

Suggested Approach

Use a hash map to store each element's value and index as you iterate through the array. For each element, check if the complement (target - current element) exists in the map; if so, return the two indices. This achieves O(n) time and O(n) space.

Pro tip: Clarify upfront whether the array is sorted or if there are constraints like duplicate values or multiple valid pairs. Mentioning edge cases like empty array or no solution shows thoroughness and can guide your implementation.

1. Clarify requirements and constraints

Ask about input size, whether the array is sorted, if there are duplicate values, and if multiple valid pairs exist. Confirm the expected return type and edge cases.

2. Choose the optimal data structure

Select a hash map (dictionary) to store values and indices for O(1) lookups, enabling a single-pass solution.

3. Iterate and check complements

Traverse the array once; for each element, compute the complement and check if it's already in the hash map. If found, return the stored index and current index.

4. Handle edge cases and return

If no pair is found after the loop, return an empty array. Ensure indices are distinct and consider duplicate values correctly.

5. Analyze complexity and test

State time and space complexity (O(n) each). Walk through a small example and test edge cases like empty array, no solution, and negative numbers.

Key Points to Mention

Hash map for O(1) lookups to achieve O(n) time complexity
Single-pass algorithm: check complement before inserting current element to avoid using the same index twice
Handling duplicate values correctly (e.g., [3,3] with target 6)
Space-time tradeoff: O(n) extra space for O(n) time improvement over brute force
Edge cases: empty array, no valid pair, negative numbers, and large inputs
Return indices in any order; ensure they are distinct

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