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Serialize and Deserialize Binary Tree is a hard coding interview question covering trees, design, strings — the kind asked at FAANG (Facebook/Meta, Apple, Amazon, Netflix, Google) and AI-first companies like Anthropic, OpenAI, and Nvidia.
Design an algorithm to serialize a binary tree to a string and deserialize it back to the original structure.
Example: tree [1, 2, 3, null, null, 4, 5] should survive a round-trip: tree -> string -> tree.
The format is up to you. The test verifies serialize(deserialize(serialize(tree))) == serialize(tree).
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