---
title: 'Hierarchical'
description: 'Recursive shape: every node roots a subtree. Solutions are recurrences.'
sidebar:
  order: 1
  label: Introduction
---

:::warning[Under construction]
This page is a scaffold. Notes, canonical problems, and template code are not written yet.
:::

## Patterns

- [DFS on Trees](/guides/coding/hierarchical/tree-dfs) — Post/pre/in-order recursion; the answer composes from subtree answers.
- [BFS on Trees](/guides/coding/hierarchical/tree-bfs) — Level-order traversal via a queue.
- [Trie](/guides/coding/hierarchical/trie) — Character-indexed tree; shared prefixes are shared paths.
- [Binary Search Tree](/guides/coding/hierarchical/binary-search-tree) — A sorted array in tree form: in-order traversal is sorted order.

**Systems anchor:** Trie is a radix routing table / IPLD path resolution; the BST invariant is a B-tree index.