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- Copyright (c) Jeremy Siek 2000, 2001
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- Distributed under the Boost Software License, Version 1.0.
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- <Head>
- <Title>Boost Graph Library: Breadth-First Visit</Title>
- <BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b"
- ALINK="#ff0000">
- <IMG SRC="../../../boost.png"
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- <BR Clear>
- <H1><A NAME="sec:bfv"><img src="figs/python.gif" alt="(Python)"/>
- <TT>breadth_first_visit</TT>
- </H1>
- <P>
- <PRE>
- template <class <a href="./IncidenceGraph.html">IncidenceGraph</a>, class P, class T, class R>
- void breadth_first_visit(IncidenceGraph& G,
- typename graph_traits<IncidenceGraph>::vertex_descriptor s,
- const bgl_named_params<P, T, R>& params);
- template <class <a href="./IncidenceGraph.html">IncidenceGraph</a>, class <a href="./Buffer.html">Buffer</a>, class <a href="./BFSVisitor.html">BFSVisitor</a>, class ColorMap>
- void breadth_first_visit
- (const IncidenceGraph& g,
- typename graph_traits<IncidenceGraph>::vertex_descriptor s,
- Buffer& Q, BFSVisitor vis, ColorMap color)
- </PRE>
- This function is basically the same as <tt>breadth_first_search()</tt>
- except that the color markers are not initialized in the
- algorithm. The user is responsible for making sure the color for every
- vertex is white before calling the algorithm. With this difference,
- the graph type is only required to be an <a
- href="./IncidenceGraph.html">Incidence Graph</a> instead of a <a
- href="./VertexListGraph.html">Vertex List Graph</a>. Also, this
- difference allows for more flexibility in the color property map. For
- example, one could use a map that only implements a partial function
- on the vertices, which could be more space efficient when the search
- only reaches a small portion of the graph.
- <H3>Where Defined</H3>
- <P>
- <a href="../../../boost/graph/breadth_first_search.hpp"><TT>boost/graph/breadth_first_search.hpp</TT></a>
- <h3>Parameters</h3>
- IN: <tt>IncidenceGraph& g</tt>
- <blockquote>
- A directed or undirected graph. The graph type must
- be a model of <a href="./IncidenceGraph.html">Incidence Graph</a>.<br>
- <b>Python</b>: The parameter is named <tt>graph</tt>.
- </blockquote>
- IN: <tt>vertex_descriptor s</tt>
- <blockquote>
- The source vertex where the search is started.<br>
- <b>Python</b>: The parameter is named <tt>root_vertex</tt>.
- </blockquote>
- <h3>Named Parameters</h3>
- IN: <tt>visitor(BFSVisitor vis)</tt>
- <blockquote>
- A visitor object that is invoked inside the algorithm at the
- event-points specified by the <a href="BFSVisitor.html">BFS
- Visitor</a> concept. The visitor object is passed by value <a
- href="#1">[1]</a>.<br> <b>Default:</b>
- <tt>bfs_visitor<null_visitor></tt><br>
- <b>Python</b>: The parameter should be an object that derives from
- the <a href="BFSVisitor.html#python"><tt>BFSVisitor</tt></a> type of the graph.
- </blockquote>
- UTIL/OUT: <tt>color_map(ColorMap color)</tt>
- <blockquote>
- This is used by the algorithm to keep track of its progress through
- the graph. The type <tt>ColorMap</tt> must be a model of <a
- href="../../property_map/doc/ReadWritePropertyMap.html">Read/Write
- Property Map</a> and its key type must be the graph's vertex
- descriptor type and the value type of the color map must model
- <a href="./ColorValue.html">ColorValue</a>.<br>
- <b>Default:</b> <tt>get(vertex_color, g)</tt><br>
- <b>Python</b>: The color map must be a <tt>vertex_color_map</tt> for
- the graph.
- </blockquote>
- UTIL: <tt>buffer(Buffer& Q)</tt>
- <blockquote>
- The queue used to determine the order in which vertices will be
- discovered. If a FIFO queue is used, then the traversal will
- be according to the usual BFS ordering. Other types of queues
- can be used, but the traversal order will be different.
- For example Dijkstra's algorithm can be implemented
- using a priority queue. The type <tt>Buffer</tt> must be a model of
- <a href="./Buffer.html">Buffer</a>.<br>
- <b>Default:</b> <tt>boost::queue</tt><br>
- <b>Python</b>: The buffer must derive from the <a
- href="./Buffer.html">Buffer</a> type for the graph.
- </blockquote>
- <H3><A NAME="SECTION001330300000000000000">
- Complexity</A>
- </H3>
- <P>
- The time complexity is <i>O(E)</i>.
- <P>
- <h3>Visitor Event Points</h3>
- <ul>
- <li><b><tt>vis.examine_vertex(u, g)</tt></b>r is invoked in each
- vertex as it is removed from the queue.
- <li><b><tt>vis.examine_edge(e, g)</tt></b> is invoked on every out-edge
- of each vertex immediately after the vertex is removed from the queue.
- <li><b><tt>vis.tree_edge(e, g)</tt></b> is invoked (in addition to
- <tt>examine_edge()</tt>) if the edge is a tree edge. The
- target vertex of edge <tt>e</tt> is discovered at this time.
- <li><b><tt>vis.discover_vertex(u, g)</tt></b> is invoked the first time the
- algorithm encounters vertex <i>u</i>. All vertices closer to the
- source vertex have been discovered, and vertices further from the
- source have not yet been discovered.
- <li><b><tt>vis.non_tree_edge(e, g)</tt></b> is invoked (in addition to
- <tt>examine_edge()</tt>) if the edge is not a tree edge.
- <li><b><tt>vis.gray_target(e, g)</tt></b> is invoked (in addition to
- <tt>non_tree_edge()</tt>) if the target vertex is colored gray at the
- time of examination. The color gray indicates that
- the vertex is currently in the queue.
- <li><b><tt>vis.black_target(e, g)</tt></b> is invoked (in addition to
- <tt>non_tree_edge()</tt>) if the target vertex is colored black at the
- time of examination. The color black indicates that the
- vertex is no longer in the queue.
- <li><b><tt>vis.finish_vertex(u, g)</tt></b> is invoked after all of the out
- edges of <i>u</i> have been examined and all of the adjacent vertices
- have been discovered.
- </ul>
- <h3>See Also</h3>
- <a href="./breadth_first_search.html"><tt>breadth_first_search()</tt></a>,
- <a href="./bfs_visitor.html"><tt>bfs_visitor</tt></a>, and
- <a href="./depth_first_search.html"><tt>depth_first_search()</tt></a>
- <h3>Notes</h3>
- <p><a name="1">[1]</a>
- Since the visitor parameter is passed by value, if your visitor
- contains state then any changes to the state during the algorithm
- will be made to a copy of the visitor object, not the visitor object
- passed in. Therefore you may want the visitor to hold this state by
- pointer or reference.
- <br>
- <HR>
- <TABLE>
- <TR valign=top>
- <TD nowrap>Copyright © 2000-2001</TD><TD>
- <A HREF="http://www.boost.org/people/jeremy_siek.htm">Jeremy Siek</A>, Indiana University (<A HREF="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</A>)
- </TD></TR></TABLE>
- </BODY>
- </HTML>
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