I went with a preorder traversal using null markers for missing nodes, which worked, but I spent way too long debating BFS vs DFS in my head before committing.
Start by clarifying requirements and constraints, then choose a serialization format (e.g., preorder with null markers) that enables unambiguous reconstruction. Implement the Codec class with serialize and deserialize methods, ensuring efficiency and handling edge cases like empty trees. Discuss trade-offs and potential optimizations.
Pro tip: Demonstrate awareness of real-world constraints by mentioning that the serialized string should be compact and that deserialization should avoid recursion depth issues for skewed trees. Also, proactively discuss how your solution would handle very large trees or streaming scenarios.
Ask about the expected tree size, whether the serialized format needs to be human-readable, and if there are any memory or performance constraints. Confirm that the tree is binary and that node values are integers.
Select a traversal order (e.g., preorder) and decide how to represent null nodes (e.g., using a sentinel like '#' or 'null'). Explain why this approach ensures unique reconstruction.
Write a recursive or iterative function that traverses the tree and appends node values and null markers to a string, using a delimiter (e.g., comma) to separate tokens.
Parse the string into tokens, then reconstruct the tree using the same traversal order, consuming tokens recursively or iteratively.
Discuss time and space complexity (O(n) for both), compare with alternative approaches (e.g., level-order, parentheses), and mention potential optimizations like using a queue for iterative deserialization to avoid stack overflow.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.