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LinkedIn·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

LinkedIn SWE interview, one coding question on tree serialization. Short and to the point, nothing fancy.

Questions Asked (1)

Q1

Implement serialize and deserialize functions for a binary tree.

Algorithms & Data Structures
Author's notes

Classic problem but I still fumbled the deserialization part a bit.

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AI HintsAI Generated

Suggested Approach

Choose a traversal order (e.g., preorder) and use a delimiter to separate node values and a marker for null nodes. Implement serialize by recursively appending values to a string, and deserialize by splitting the string and recursively reconstructing the tree.

Pro tip: Discuss trade-offs between different serialization formats (e.g., string vs. binary) and mention that your solution should handle edge cases like empty trees and large trees efficiently.

1. Clarify requirements

Ask about the expected format (string, binary), constraints (tree size, value range), and whether the serialized data needs to be human-readable.

2. Choose traversal and encoding

Select a traversal order (preorder is common) and decide on delimiters and null markers. Ensure the encoding is unambiguous.

3. Implement serialize

Recursively traverse the tree, appending node values and null markers to a string (or list) with delimiters.

4. Implement deserialize

Split the serialized string into tokens, then recursively rebuild the tree using the same traversal order.

5. Test and optimize

Test with edge cases (empty tree, skewed tree) and discuss time/space complexity. Consider optimizations like using a queue for iterative deserialization.

Key Points to Mention

  • Choice of traversal order (preorder, inorder, postorder, level-order) and why it matters
  • Use of delimiters and null markers to ensure unambiguous serialization
  • Handling of edge cases: empty tree, single node, skewed tree
  • Time and space complexity: O(n) time and O(n) space for both operations
  • Trade-offs between different serialization formats (e.g., string vs. binary, human-readable vs. compact)
  • Potential optimizations: iterative approach, using StringBuilder for efficiency

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