Adjacency List

FCC link

Graphs can be represented in different ways. Here we describe one way, which is called an adjacency list. An adjacency list is essentially a bulleted list where the left side is the node and the right side lists all the other nodes it's connected to. Below is a representation of an adjacency list.

Node1: Node2, Node3

Node2: Node1

Node3: Node1

Above is an undirected graph because Node1 is connected to Node2 and Node3, and that information is consistent with the connections Node2 and Node3 show. An adjacency list for a directed graph would mean each row of the list shows direction. If the above was directed, then Node2: Node1 would mean there the directed edge is pointing from Node2 towards Node1. We can represent the undirected graph above as an adjacency list by putting it within a JavaScript object.

var undirectedG = {
  Node1: ["Node2", "Node3"],
  Node2: ["Node1"],
  Node3: ["Node1"],
};

This can also be more simply represented as an array where the nodes just have numbers rather than string labels.

var undirectedGArr = [
  [1, 2], // Node1
  [0], // Node2
  [0], // Node3
];