Let's define a textual representation of the graph that we'll use in the following examples.
Create the following as graph.txt:
12,3,40C 21,4 31,5,6 41,2 53,6 63,5 76
We defined a file structure that will represent our graph, based somewhat on the adjacency list approach. We assumed that each node has a unique ID and the file structure has four fields, as follows:
The node ID
A comma-separated list of neighbors
The distance from the start node
The node status
In the initial representation, only the starting node has values for the third and fourth columns: its distance from itself is 0 and its status is "C", which we'll explain later.
Our graph is directional—more formally referred to as a directed graph—that is to say, if node 1 lists node 2 as a neighbor, there is only a return path if node 2 also lists node 1 as its neighbor. We see this in the graphical representation where all but one edge has an arrow on both ends.