Adjacency List

In the adjacency list representation of a graph, each node has a list of nodes that are adjacent to it, i.e. connected by an edge. A linked list is a natural representation.

1	(5 2)
2	(3 5 1)
3	(4 2)
4	(6 3 5)
5	(4 2 1)
6	(4)

This graph is undirected, so each link is represented twice.

The storage required is O(|V| + |E|). This is a good representation if the graph is sparse, i.e. each node is not linked to many others.