serialize deserialize binary tree (#9625)

* added serialize and desrialize bin tree

* format files

* added type hints

* added type hints

* Use dataclass .__eq__(), .__iter__(), and .__repr__()

---------

Co-authored-by: Christian Clauss <cclauss@me.com>

data_structures/binary_tree/serialize_deserialize_binary_tree.py

@@ -0,0 +1,140 @@
+from __future__ import annotations
+
+from collections.abc import Iterator
+from dataclasses import dataclass
+
+
+@dataclass
+class TreeNode:
+    """
+    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.
+    """
+
+    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]:
+        """
+        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)
+        """
+        yield self
+        yield from self.left or ()
+        yield from self.right or ()
+
+    def __len__(self) -> int:
+        """
+        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
+        """
+        return sum(1 for _ in self)
+
+    def __repr__(self) -> str:
+        """
+        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'
+        """
+        return f"{self.value},{self.left!r},{self.right!r}".replace("None", "null")
+
+    @classmethod
+    def five_tree(cls) -> TreeNode:
+        """
+        >>> repr(TreeNode.five_tree())
+        '1,2,null,null,3,4,null,null,5,null,null'
+        """
+        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:
+    """
+    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.
+    """
+
+    if not data:
+        raise ValueError("Data cannot be empty.")
+
+    # Split the serialized string by a comma to get node values
+    nodes = data.split(",")
+
+    def build_tree() -> TreeNode | None:
+        # Get the next value from the list
+        value = nodes.pop(0)
+
+        if value == "null":
+            return None
+
+        node = TreeNode(int(value))
+        node.left = build_tree()  # Recursively build left subtree
+        node.right = build_tree()  # Recursively build right subtree
+        return node
+
+    return build_tree()
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()