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

Intermediate
Jun 2026

Summary

Amazon SWE coding round with a graph/greedy problem on a circular hub network. The problem statement was a bit vague on the edge weight definition since the screenshot cut off the constraints and expected output, which made it harder to fully verify a solution.

Questions Asked (1)

Q1

A drone starts at hub 1 on a circular network of m hubs and must visit a sequence of requested hubs in order. Given travel times between adjacent hubs, compute the minimum total travel time to fulfill all requests.

Algorithms & Data Structures
Author's notes

The circular structure is the key part.

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AI HintsAI Generated

Suggested Approach

Model the circular network as a graph where each hub is a node and edges represent travel times between adjacent hubs. Precompute the shortest travel time between any two hubs by considering both clockwise and counterclockwise paths around the circle. Then, sum the precomputed shortest times for each consecutive pair in the requested sequence, starting from hub 1.

Pro tip: Clarify whether the drone must visit hubs in the exact order given or if it can optimize the order; the problem states 'in order', so assume fixed order. Also, mention that the solution runs in O(m + n) time, which is optimal.

1. Understand the problem and constraints

Restate the problem: a circular network of m hubs, start at hub 1, visit a sequence of requested hubs in order, minimize total travel time. Clarify that travel times are given for adjacent hubs and that the drone can move clockwise or counterclockwise.

2. Precompute distances between all pairs of hubs

Since the network is circular, the shortest path between any two hubs is the minimum of the clockwise and counterclockwise distances. Compute prefix sums of edge weights to quickly calculate these distances in O(1) per query.

3. Compute total travel time for the sequence

Initialize total time to 0 and current hub to 1. For each requested hub in the given order, add the shortest distance from current hub to that hub, then update current hub to the requested hub.

4. Analyze time and space complexity

Precomputing prefix sums takes O(m) time and O(m) space. Processing the sequence takes O(n) time, where n is the number of requests. Overall O(m + n) time, which is optimal.

5. Consider edge cases and validate

Handle cases where the sequence is empty, contains hub 1, or has repeated hubs. Ensure the circular distance calculation correctly handles wrap-around (e.g., from hub m to hub 1).

Key Points to Mention

  • Circular network representation: hubs arranged in a circle with given travel times between adjacent hubs.
  • Shortest path between two hubs on a circle: min(clockwise distance, counterclockwise distance).
  • Precomputation using prefix sums to enable O(1) distance queries.
  • Sequential processing of requests: sum distances between consecutive hubs in the given order.
  • Time complexity: O(m + n) for m hubs and n requests, which is optimal.
  • Edge cases: empty request list, starting hub included in requests, wrap-around distances.

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