Directed Versus Undirected Graphs
![](/assets/images2/undirected-graph.png)
Undirected graph
(no arrows)
One of the key distinctions people make between graphs is whether they are directed or undirected. I'll admit, when I see the phrase "undirected graph," I sometimes get a mental image of a subway system map just sitting there aimlessly on the couch while its parents ask when it's going to take responsibility and do something with its life...
![](/assets/images2/directed-graph.png)
Directed graph
(note the arrows)
...but that's just me. Really, all we're saying is whether the edges in a graph are bidirectional or not.
Most, but not all, graphs I've seen have only one kind of edge. There are a few cases where you might want to use both—for example, a street map might have undirected edges for two-way streets and directed edges for one-way streets—but that's the only example I can think of off the top of my head.
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