a binary tree node has a value left child and right child props value the value of the node left the left child of the node right the right child of the node iterate through the tree in preorder returns an iterator of the tree nodes listtreenode1 1 null null tupletreenode1 treenode2 treenode3 1 2 null null 3 null null 2 null null 3 null null count the number of nodes in the tree returns the number of nodes in the tree lentreenode1 1 lentreenode1 treenode2 treenode3 3 represent the tree as a string returns a string representation of the tree reprtreenode1 1 null null reprtreenode1 treenode2 treenode3 1 2 null null 3 null null reprtreenode1 treenode2 treenode3 treenode4 treenode5 1 2 null null 3 4 null null 5 null null reprtreenode fivetree 1 2 null null 3 4 null null 5 null null deserialize a string to a binary tree args datastr the serialized string returns the root of the binary tree root treenode fivetree serialzeddata reprroot deserialized deserializeserialzeddata root deserialized true root is deserialized two separate trees false root right right value 6 root deserialized false serialzeddata reprroot deserialized deserializeserialzeddata root deserialized true deserialize traceback most recent call last valueerror data cannot be empty split the serialized string by a comma to get node values get the next value from the list a binary tree node has a value left child and right child props value the value of the node left the left child of the node right the right child of the node iterate through the tree in preorder returns an iterator of the tree nodes list treenode 1 1 null null tuple treenode 1 treenode 2 treenode 3 1 2 null null 3 null null 2 null null 3 null null count the number of nodes in the tree returns the number of nodes in the tree len treenode 1 1 len treenode 1 treenode 2 treenode 3 3 represent the tree as a string returns a string representation of the tree repr treenode 1 1 null null repr treenode 1 treenode 2 treenode 3 1 2 null null 3 null null repr treenode 1 treenode 2 treenode 3 treenode 4 treenode 5 1 2 null null 3 4 null null 5 null null repr treenode five_tree 1 2 null null 3 4 null null 5 null null deserialize a string to a binary tree args data str the serialized string returns the root of the binary tree root treenode five_tree serialzed_data repr root deserialized deserialize serialzed_data root deserialized true root is deserialized two separate trees false root right right value 6 root deserialized false serialzed_data repr root deserialized deserialize serialzed_data root deserialized true deserialize traceback most recent call last valueerror data cannot be empty split the serialized string by a comma to get node values get the next value from the list recursively build left subtree recursively build right subtree
from __future__ import annotations

from collections.abc import Iterator
from dataclasses import dataclass


@dataclass
class TreeNode:
    

    value: int = 0
    left: TreeNode | None = None
    right: TreeNode | None = None

    def __post_init__(self):
        if not isinstance(self.value, int):
            raise TypeError("Value must be an integer.")

    def __iter__(self) -> Iterator[TreeNode]:
        
        yield self
        yield from self.left or ()
        yield from self.right or ()

    def __len__(self) -> int:
        
        return sum(1 for _ in self)

    def __repr__(self) -> str:
        
        return f"{self.value},{self.left!r},{self.right!r}".replace("None", "null")

    @classmethod
    def five_tree(cls) -> TreeNode:
        
        root = TreeNode(1)
        root.left = TreeNode(2)
        root.right = TreeNode(3)
        root.right.left = TreeNode(4)
        root.right.right = TreeNode(5)
        return root


def deserialize(data: str) -> TreeNode | None:
    

    if not data:
        raise ValueError("Data cannot be empty.")

    
    nodes = data.split(",")

    def build_tree() -> TreeNode | None:
        
        value = nodes.pop(0)

        if value == "null":
            return None

        node = TreeNode(int(value))
        node.left = build_tree()  
        node.right = build_tree()  
        return node

    return build_tree()


if __name__ == "__main__":
    import doctest

    doctest.testmod()