serialize deserialize binary tree

data_structures/binary_tree/serialize_deserialize_binary_tree.py

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+from __future__ import annotations
+
+
+class TreeNode:
+    """
+    A binary tree node has a value, left child, and right child.
+
+    Props:
+        val(int): The value of the node.
+        left: The left child of the node.
+        right: The right child of the node.
+    """
+
+    def __init__(
+        self,
+        val: int = 0,
+        left: TreeNode | None = None,
+        right: TreeNode | None = None,
+    ) -> None:
+        if not isinstance(val, int):
+            raise TypeError("Value must be an integer.")
+        self.val = val
+        self.left = left
+        self.right = right
+
+
+# Helper functions
+def are_trees_identical(root1: TreeNode | None, root2: TreeNode | None) -> bool:
+    """
+    Check if two binary trees are identical.
+
+    Args:
+        root1 (TreeNode): Tree 1
+        root2 (TreeNode): Tree 2
+
+    Returns:
+        bool: True if the trees are identical, False otherwise.
+
+    >>> root1 = TreeNode(1)
+    >>> root1.left = TreeNode(2)
+    >>> root1.right = TreeNode(3)
+    >>> root2 = TreeNode(1)
+    >>> root2.left = TreeNode(2)
+    >>> root2.right = TreeNode(3)
+    >>> are_trees_identical(root1, root2)
+    True
+    >>> root1 = TreeNode(1)
+    >>> root1.left = TreeNode(2)
+    >>> root1.right = TreeNode(3)
+    >>> root2 = TreeNode(1)
+    >>> root2.left = TreeNode(2)
+    >>> root2.right = TreeNode(4)
+    >>> are_trees_identical(root1, root2)
+    False
+    """
+
+    if not root1 and not root2:
+        return True
+    if not root1 or not root2:
+        return False
+
+    return (
+        root1.val == root2.val
+        and are_trees_identical(root1.left, root2.left)
+        and are_trees_identical(root1.right, root2.right)
+    )
+
+
+# Main functions
+def serialize(root: TreeNode | None) -> str:
+    """
+    Serialize a binary tree to a string using preorder traversal.
+
+    Args:
+        root(TreeNode): The root of the binary tree.
+
+    Returns:
+        A string representation of the binary tree.
+
+    >>> root = TreeNode(1)
+    >>> root.left = TreeNode(2)
+    >>> root.right = TreeNode(3)
+    >>> root.right.left = TreeNode(4)
+    >>> root.right.right = TreeNode(5)
+    >>> serialize(root)
+    '1,2,null,null,3,4,null,null,5,null,null'
+    >>> root = TreeNode(1)
+    >>> serialize(root)
+    '1,null,null'
+    """
+
+    # Use "null" to represent empty nodes in the serialization
+    if not root:
+        return "null"
+
+    return str(root.val) + "," + serialize(root.left) + "," + serialize(root.right)
+
+
+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(1)
+    >>> root.left = TreeNode(2)
+    >>> root.right = TreeNode(3)
+    >>> root.right.left = TreeNode(4)
+    >>> root.right.right = TreeNode(5)
+    >>> serialzed_data = serialize(root)
+    >>> deserialized = deserialize(serialzed_data)
+    >>> are_trees_identical(root, deserialized)
+    True
+    >>> root = TreeNode(1)
+    >>> serialzed_data = serialize(root)
+    >>> dummy_data = "1,2,null,null,3,4,null,null,5,null,null"
+    >>> deserialized = deserialize(dummy_data)
+    >>> are_trees_identical(root, deserialized)
+    False
+    >>> deserialize("")
+    Traceback (most recent call last):
+        ...
+    ValueError: Data cannot be empty.
+    """
+
+    if data == "":
+        raise ValueError("Data cannot be empty.")
+
+    # Split the serialized string by comma to get node values
+    nodes = data.split(",")
+
+    def build_tree() -> TreeNode | None:
+        # Get the next value from the list
+        val = nodes.pop(0)
+
+        if val == "null":
+            return None
+
+        node = TreeNode(int(val))
+        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()