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Google·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
Apr 2026

Summary

Google SWE interview with a graph/tree traversal problem dressed up in a fun theme. The chicken ancestor question sounds silly but it's a real algorithmic problem and they pushed into complexity tradeoffs pretty quickly.

Questions Asked (1)

Q1

Given a set of chickens and their parent-child relationships, write a function that determines whether two given chickens share a common ancestor. Also discuss what data structures you'd use to store the relationships and what the time and space complexity looks like.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

The chicken framing is funny but don't let it distract you, it's just an ancestor graph problem.

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AI HintsAI Generated

Suggested Approach

Clarify that the relationships form a forest (or tree) and choose an appropriate data structure like adjacency lists for parent-to-child links. For the ancestor check, use DFS/BFS from one chicken to find all ancestors, then check if the other chicken is in that set; alternatively, find ancestors of both and intersect. Discuss time and space complexity based on the chosen approach.

Pro tip: Mention that if the tree is large and queries are frequent, you can preprocess with binary lifting or Euler tour + RMQ to answer ancestor queries in O(1) or O(log n) time. Also, consider edge cases like the same chicken, direct parent-child, and disconnected components.

1. Clarify the problem and assumptions

Ask if the relationships form a tree or forest, if there are cycles, and if the chickens are identified by unique IDs. Confirm whether we need to handle multiple queries or just one.

2. Choose data structures

Represent the relationships using an adjacency list (e.g., dictionary mapping parent to list of children) or a parent pointer map. For efficient ancestor checks, consider building a set of ancestors for one chicken.

3. Design the algorithm

Use DFS or BFS to traverse from one chicken up to the root, collecting all ancestors. Then check if the other chicken is in that set. Alternatively, traverse both upward simultaneously and look for intersection.

4. Analyze complexity

Time complexity: O(N) for traversal in the worst case, where N is the number of chickens. Space complexity: O(N) for storing ancestors or recursion stack. Mention that with preprocessing, queries can be faster.

5. Discuss optimizations and trade-offs

For multiple queries, preprocess the tree with binary lifting or Euler tour to answer in O(log N) or O(1). Discuss trade-offs between preprocessing time and query time.

Key Points to Mention

  • Use of adjacency list or parent pointers to represent the relationships.
  • DFS/BFS for ancestor traversal, with a set for O(1) lookup.
  • Time complexity O(N) for a single query, space O(N).
  • Optimizations like binary lifting for frequent queries.
  • Handling edge cases: same chicken, direct parent, disconnected components.
  • Clarifying assumptions about the structure (tree vs forest, cycles).

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