Serialize / Deserialize Binary Tree with N-ary Follow-up

Senior tech phone-screen prompt. Implement serialization and deserialization for a binary tree, then extend the scheme to an N-ary tree. The interviewer asks the candidate to invent test cases and run code. Requirements Implement a serializer that converts a binary tree into a string or sequence representation. Implement a deserializer that reconstructs the original binary tree from that representation. The round expects runnable code and candidate-created tests. Follow-up: extend the same idea to an N-ary tree. The representation must preserve enough null / child-boundary information to reconstruct shape, not only values. Notes Clarify node value constraints and whether duplicate values are allowed; serialization must not rely on uniqueness. For the N-ary follow-up, the key is encoding child counts or explicit delimiters so the parser knows where each node's child list ends. Bring your own tests: empty tree, single node, asymmetric tree, duplicate values, and an N-ary node with zero / one / many children. Preparation Practice preorder-with-null-markers and level-order-with-null-markers for binary trees. Write one N-ary serializer using (value, child_count) records and one using bracket delimiters. Rehearse explaining why values alone cannot reconstruct tree shape.