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Google·Machine Learning Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Google ML engineer interview, got a tree problem which felt a bit out of left field for the role but wasn't the worst thing in the world.

Questions Asked (1)

Q1

Write a function to calculate the height of a binary tree.

Algorithms & Data Structures
Author's notes

Pretty classic recursion problem.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the definition of height (number of edges vs. nodes) and handling edge cases like an empty tree. Then present a recursive solution that computes the height as 1 + max(height(left), height(right)), and optionally discuss iterative approaches or optimizations.

Pro tip: Mention that recursion depth can be O(n) for skewed trees, so an iterative BFS solution may be safer in production to avoid stack overflow. Also, relate the problem to ML contexts like decision tree depth, showing domain awareness.

1. Clarify the problem

Ask whether height is defined by nodes or edges, and confirm the tree can be empty. This shows attention to detail and avoids ambiguity.

2. Outline the recursive approach

Explain that the height of a tree is 1 + the maximum height of its left and right subtrees, with a base case of 0 for an empty tree.

3. Write the code

Implement the recursive function in a clean, readable manner, handling null nodes and returning the computed height.

4. Analyze complexity

State that time complexity is O(n) since each node is visited once, and space complexity is O(h) for recursion stack, where h is the height.

5. Discuss alternatives and edge cases

Mention iterative BFS/DFS solutions, potential stack overflow for skewed trees, and how this applies to ML (e.g., decision tree depth).

Key Points to Mention

  • Definition of height: number of edges on the longest path from root to leaf (or nodes, clarify).
  • Base case: empty tree has height 0 (or -1 if edges).
  • Recursive formula: height = 1 + max(height(left), height(right)).
  • Time complexity O(n), space complexity O(h) for recursion.
  • Iterative alternative using level-order traversal (BFS) to avoid recursion depth issues.
  • Relevance to ML: tree depth affects model complexity and overfitting in decision trees.

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