← Jane Street Interview Insights
Two things happening at once here: reversing the cipher and parsing the serialized tree structure.
First, clarify the serialization format and cipher details, then design a recursive parser that builds the tree while decrypting each node's text. Use a stack or recursion to handle pre-order traversal, ensuring children are ordered correctly. Finally, convert the tree to nested lists and test with edge cases.
Pro tip: Discuss how you would handle malformed input or ambiguous serialization, and mention that you'd write unit tests for edge cases like empty trees or single nodes. This shows attention to robustness and quality.
Ask questions to confirm the exact serialization format (e.g., how nodes and children are delimited) and the substitution cipher mapping (e.g., is it a simple shift or a full mapping?).
Outline a recursive descent parser or an iterative stack-based approach that reads the pre-order string and constructs the tree, decrypting each node's text as it is parsed.
Apply the substitution cipher to each node's text, ensuring that the decryption is done correctly and efficiently, possibly using a precomputed mapping.
Traverse the constructed tree and produce the required nested list representation, where each node is a list containing its decrypted text and a list of its children.
Walk through examples, including edge cases (empty string, single node, deep tree), and discuss how to handle errors or malformed input.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.