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Amazon·Software Engineer·Onsite - Coding / Algorithms·Intermediate

IntermediatePrefer not to say
Jun 2026

Summary

Amazon SWE coding round with a graph problem that was more involved than it looked at first glance. Doable if you know your DFS, but the max-diff twist across connected components added a wrinkle I wasn't fully ready for.

Questions Asked (1)

Q1

Given a graph defined by a list of vertices with integer values, a start vertex list, and an end vertex list, find the maximum difference between the max and min vertex values across all connected components.

Algorithms & Data Structures
Author's notes

The setup took me a minute to parse.

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AI HintsAI Generated

Suggested Approach

Model the problem as finding connected components in an undirected graph, then for each component compute the difference between its maximum and minimum vertex values. Return the maximum difference across all components. Use Union-Find or BFS/DFS to identify components efficiently.

Pro tip: Clarify edge cases upfront, such as empty graph, single vertex, or disconnected vertices with no edges. Also, discuss time and space complexity trade-offs between Union-Find and BFS/DFS.

1. Understand the problem and clarify inputs

Confirm that the graph is undirected, vertices have integer values, and edges are given as start and end lists. Ask about edge cases like isolated vertices or empty input.

2. Choose a component-finding algorithm

Decide between Union-Find (disjoint set) or BFS/DFS. Consider factors like graph size, density, and whether you need to process components on the fly.

3. Build the graph and find components

Construct adjacency lists or initialize Union-Find. Traverse the graph to group vertices into connected components.

4. Compute min and max per component

For each component, track the minimum and maximum vertex values. Compute the difference and update the global maximum.

5. Return the result and analyze complexity

Return the maximum difference found. State time and space complexity: O(V+E) for BFS/DFS or O(E α(V)) for Union-Find, with O(V) space.

Key Points to Mention

  • Connected components in an undirected graph
  • Union-Find (Disjoint Set Union) with path compression and union by rank
  • BFS/DFS traversal for component identification
  • Tracking min and max values per component
  • Handling edge cases: empty graph, single vertex, isolated vertices
  • Time and space complexity analysis

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