## TL;DR

Graph theory studies networks of vertices connected by edges. Applications: social networks, routing algorithms, dependency resolution, compiler optimization (register allocation via graph coloring), circuit design. Euler's 1736 Bridges of Konigsberg paper founded the field.

## Core Explanation

Directed vs. undirected. Weighted graphs model distances/costs. Complete graph K_n: every vertex connected to every other. Bipartite graph: vertices can be partitioned into two independent sets. Planar graph: can be drawn without edge crossings (Euler's formula: V - E + F = 2). Trees are connected acyclic graphs. Spanning trees connect all vertices with minimum edges.

## Further Reading

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