uot;(&quot; &lt;&lt; index[src] &lt;&lt; &quot;,&quot; &lt;&lt; index[targ] &lt;&lt; &quot;) &quot;;
      }
      std::cout &lt;&lt; std::endl;
      //...
    }
    //...
  };
</pre>
For vertex 0 the output is:
<pre>
  in-edges: (2,0) (3,0) (4,0)
</pre>
<p>&nbsp;
<h3>Adjacent Vertices</h3>
<p>Given the out-edges of a vertex, the target vertices of these edges are <i>adjacent</i>
to the source vertex. Sometimes an algorithm does not need to look at the edges
of the graph and only cares about the vertices. 