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

Intermediate
Jun 2026

Summary

Palantir code review round for a software engineer role, focused on a graph problem involving city roads. The class structure was dense enough to slow things down, and there was a classic bug hiding in plain sight.

Questions Asked (1)

Q1

You are given a code snippet modeling a road network with classes for locations, roads, and road connections. Review the code, identify bugs, and explain how you would traverse the graph correctly.

Algorithms & Data StructuresRoot Cause AnalysisTechnical Trade-offs
Author's notes

The class setup is genuinely messy to read.

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AI HintsAI Generated

Suggested Approach

First, systematically review the code to identify bugs such as incorrect edge directions, missing visited tracking, or improper data structures. Then, explain the correct graph traversal algorithm (BFS/DFS) for the road network, emphasizing how to handle directed/undirected edges and avoid infinite loops. Finally, discuss trade-offs and potential optimizations.

Pro tip: Demonstrate a methodical debugging process by walking through a small example, and mention how you would test the traversal with edge cases like disconnected components or cycles.

1. Understand the Code and Model

Review the classes (Location, Road, RoadConnection) to understand the intended graph representation, including whether edges are directed or undirected and how connections are stored.

2. Identify Bugs

Look for common bugs: incorrect edge direction, missing visited set causing infinite loops, off-by-one errors, or improper data structure usage (e.g., using a list instead of a set for visited).

3. Explain Correct Traversal

Describe the correct BFS or DFS algorithm, including initialization, queue/stack usage, visited tracking, and handling of directed/undirected edges. Mention how to adapt for weighted edges if needed.

4. Discuss Trade-offs and Optimizations

Compare BFS vs DFS for this scenario (e.g., shortest path vs memory), and suggest improvements like using adjacency lists for sparse graphs or bidirectional search for performance.

5. Validate with Examples

Walk through a small example to demonstrate the bug and the corrected traversal, and mention edge cases like cycles, disconnected graphs, or self-loops.

Key Points to Mention

  • Directed vs undirected edges and their impact on traversal
  • Importance of a visited set to prevent infinite loops in cyclic graphs
  • BFS vs DFS: use cases, time/space complexity, and suitability for road networks
  • Common bugs: incorrect edge direction, missing visited tracking, off-by-one errors
  • Handling disconnected components and ensuring all nodes are visited
  • Trade-offs between adjacency list and adjacency matrix representations

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