Tree Structures — Vocabulary and Rooted Trees

A tree is nodes connected without cycles; one root defines parent/child direction. The plural skill trees reminds you that forests and subtrees use the same tools.

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

# Tiny example: root with two children
root = TreeNode(1, TreeNode(2), TreeNode(3))
print(root.val, root.left.val if root.left else None)

Key takeaways

• Edges are directed away from the root in most interview stories.
• Height vs depth: measure from leaves vs from root.
• Subtrees are themselves trees—recursion loves this.