b> <tt>dijkstra_visitor&lt;null_visitor&gt;</tt><br>
</blockquote>


<H3>Complexity</H3>

<P>
The time complexity is <i>O(V log V + E)</i>.


<h3>Visitor Event Points</h3>

<ul>
<li><b><tt>vis.initialize_vertex(u, g)</tt></b>
  is invoked on each vertex in the graph before the start of the
  algorithm.
<li><b><tt>vis.examine_vertex(u, g)</tt></b>
  is invoked on a vertex as it is removed from the priority queue
  and added to set <i>S</i>. At this point we know that <i>(p[u],u)</i>
  is a shortest-paths tre