e, if we wish to model a simplistic map
of the United States interstate highway system, we might state that
the vertices of the graph are cities and the edges are highways, then
define the information that we maintain for each city and highway:</p>
<pre class="literal-block">
struct City {
  City() { }
  City(const std::string&amp; name, const std::string&amp; mayor = &quot;Unknown&quot;, int population = 0)
    : name(name), mayor(mayor), population(population) { }

  std::string name;
  std::string mayor;