# Edge Classification in Directed Graphs

Learn how to classify edges in a directed graph using depth-first search.

## We'll cover the following

Edges of a directed graph are classified into four categories depending on when they are first explored during a depth-first search.

This classification of edges is easily done by making small changes to depth-first search and is surprisingly useful when designing other applications of depth-first search.

## Classification of edges

The edges of a directed graph that become part of the depth-first tree or the depth-first forest are called **tree-edges**. The remaining non-tree edges are classified depending on the relationship between its end-vertices.

Get hands-on with 1200+ tech skills courses.