The problem looks clean on paper but the null handling is where things get messy.
Choose a traversal order (preorder or level-order) that allows unambiguous reconstruction, and use a delimiter and null marker to encode the tree into a string. Then implement the inverse process by parsing the string and recursively or iteratively rebuilding the tree.
Pro tip: Discuss trade-offs between preorder and level-order serialization, and mention how to handle edge cases like empty trees and large trees to show production readiness.
Ask about the tree's properties (e.g., binary search tree, complete tree), expected input size, and whether the serialized string needs to be human-readable or compact.
Select a traversal order (e.g., preorder) and define a format using delimiters and a null marker (e.g., '#' for null, ',' as delimiter).
Write a function that traverses the tree and appends node values and null markers to a string, ensuring proper handling of empty trees.
Write a function that parses the string (e.g., using a queue or index pointer) and reconstructs the tree recursively or iteratively.
Walk through examples, test edge cases (empty tree, skewed tree), and compare your approach with alternatives like level-order serialization.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.