Tree node copying — clone

Recursive copy; random ptr — old→new map.

Try this in Python

from __future__ import annotations
from dataclasses import dataclass


@dataclass
class TreeNode:
    val: int
    left: TreeNode | None = None
    right: TreeNode | None = None


def clone(root: TreeNode | None) -> TreeNode | None:
    if not root:
        return None
    return TreeNode(root.val, clone(root.left), clone(root.right))

r = TreeNode(1, TreeNode(2), TreeNode(3))
c = clone(r)
print(c.val, c.left.val if c.left else None)

Key takeaways

• Deep copy default.
• Iterative — traversal stack.
• Alias vs share.