Store an AVL Tree

MediumPython

Problem

How would you store an AVL tree?

Implement serialize_avl(root) to encode the tree structure using preorder traversal and None markers for missing children. The input is a nested list [key, left, right], or None for an empty tree. Return a flat list that preserves every key and child relationship, including the empty tree case.

Constraints

0 <= number of nodes <= 10^4
Each key is an integer
Keys are unique
The input tree satisfies the binary-search-tree ordering property
The input tree is AVL-balanced

Function Signature

def serialize_avl(root):

CodePython 3

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