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Palantir·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Palantir software engineer round with a graph traversal question. Pretty standard stuff, nothing too wild.

Questions Asked (1)

Q1

Given a graph of cities where all edge weights are equal to 1, find the shortest path between two cities.

Algorithms & Data Structures
Author's notes

Straightforward BFS, which is exactly what you'd reach for when all edges cost the same.

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AI HintsAI Generated

Suggested Approach

Since all edge weights are equal to 1, the shortest path can be found using BFS, which explores level by level and guarantees the shortest path in unweighted graphs. Start BFS from the source, track visited nodes and parent pointers, and stop when the destination is reached. Reconstruct the path by backtracking from the destination using the parent pointers.

Pro tip: Mention that BFS is optimal for unweighted graphs, but if the graph is very large and you only need the distance (not the path), bidirectional BFS can be more efficient. Also, clarify whether the graph is directed or undirected, as it affects traversal.

1. Clarify assumptions

Confirm that the graph is unweighted (all edges weight 1), whether it's directed or undirected, and whether you need the actual path or just the distance.

2. Choose BFS

Explain that BFS is the standard algorithm for shortest path in unweighted graphs, with O(V+E) time complexity.

3. Describe BFS traversal

Outline the BFS process: use a queue, mark visited nodes, and track parent pointers for path reconstruction.

4. Reconstruct path

Once the destination is reached, backtrack from destination to source using parent pointers to build the path.

5. Analyze complexity and edge cases

State time and space complexity, and discuss edge cases like disconnected graphs or source equals destination.

Key Points to Mention

  • BFS guarantees shortest path in unweighted graphs
  • Time complexity O(V+E), space O(V)
  • Use of queue and visited set to avoid cycles
  • Parent pointers for path reconstruction
  • Handling disconnected graphs (return no path)
  • Alternative: bidirectional BFS for efficiency

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