---
title: 'Relational'
description: 'Arbitrary edges; you must track visited. Trees are acyclic connected graphs with less bookkeeping.'
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 Graphs](/guides/coding/relational/graph-dfs) — Exhaustive reachability: recursion plus a visited set.
- [BFS on Graphs](/guides/coding/relational/graph-bfs) — Frontier expansion: shortest path in unweighted graphs, always.
- [Topological Sort](/guides/coding/relational/topological-sort) — Reversed DFS post-order, or Kahn's in-degree queue over a DAG.
- [Union-Find](/guides/coding/relational/union-find) — Incremental connectivity without traversal.

**Systems anchor:** Topological sort is dependency resolution; union-find is partition detection; BFS is gossip propagation.