187 lines
6.6 KiB
HTML
187 lines
6.6 KiB
HTML
<HTML>
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<!--
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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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(See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt)
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-->
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<Head>
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<Title>Boost Graph Library: Breadth-First Visit</Title>
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<BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b"
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ALINK="#ff0000">
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<IMG SRC="../../../boost.png"
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ALT="C++ Boost" width="277" height="86">
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<BR Clear>
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<H1><A NAME="sec:bfv"><img src="figs/python.gif" alt="(Python)"/>
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<TT>breadth_first_visit</TT>
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</H1>
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<P>
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<PRE>
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template <class <a href="./IncidenceGraph.html">IncidenceGraph</a>, class P, class T, class R>
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void breadth_first_visit(IncidenceGraph& G,
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typename graph_traits<IncidenceGraph>::vertex_descriptor s,
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const bgl_named_params<P, T, R>& params);
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template <class <a href="./IncidenceGraph.html">IncidenceGraph</a>, class <a href="./Buffer.html">Buffer</a>, class <a href="./BFSVisitor.html">BFSVisitor</a>, class ColorMap>
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void breadth_first_visit
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(const IncidenceGraph& g,
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typename graph_traits<IncidenceGraph>::vertex_descriptor s,
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Buffer& Q, BFSVisitor vis, ColorMap color)
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</PRE>
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This function is basically the same as <tt>breadth_first_search()</tt>
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except that the color markers are not initialized in the
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algorithm. The user is responsible for making sure the color for every
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vertex is white before calling the algorithm. With this difference,
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the graph type is only required to be an <a
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href="./IncidenceGraph.html">Incidence Graph</a> instead of a <a
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href="./VertexListGraph.html">Vertex List Graph</a>. Also, this
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difference allows for more flexibility in the color property map. For
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example, one could use a map that only implements a partial function
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on the vertices, which could be more space efficient when the search
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only reaches a small portion of the graph.
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<H3>Where Defined</H3>
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<P>
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<a href="../../../boost/graph/breadth_first_search.hpp"><TT>boost/graph/breadth_first_search.hpp</TT></a>
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<h3>Parameters</h3>
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IN: <tt>IncidenceGraph& g</tt>
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<blockquote>
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A directed or undirected graph. The graph type must
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be a model of <a href="./IncidenceGraph.html">Incidence Graph</a>.<br>
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<b>Python</b>: The parameter is named <tt>graph</tt>.
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</blockquote>
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IN: <tt>vertex_descriptor s</tt>
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<blockquote>
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The source vertex where the search is started.<br>
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<b>Python</b>: The parameter is named <tt>root_vertex</tt>.
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</blockquote>
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<h3>Named Parameters</h3>
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IN: <tt>visitor(BFSVisitor vis)</tt>
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<blockquote>
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A visitor object that is invoked inside the algorithm at the
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event-points specified by the <a href="BFSVisitor.html">BFS
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Visitor</a> concept. The visitor object is passed by value <a
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href="#1">[1]</a>.<br> <b>Default:</b>
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<tt>bfs_visitor<null_visitor></tt><br>
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<b>Python</b>: The parameter should be an object that derives from
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the <a href="BFSVisitor.html#python"><tt>BFSVisitor</tt></a> type of the graph.
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</blockquote>
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UTIL/OUT: <tt>color_map(ColorMap color)</tt>
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<blockquote>
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This is used by the algorithm to keep track of its progress through
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the graph. The type <tt>ColorMap</tt> must be a model of <a
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href="../../property_map/doc/ReadWritePropertyMap.html">Read/Write
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Property Map</a> and its key type must be the graph's vertex
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descriptor type and the value type of the color map must model
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<a href="./ColorValue.html">ColorValue</a>.<br>
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<b>Default:</b> <tt>get(vertex_color, g)</tt><br>
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<b>Python</b>: The color map must be a <tt>vertex_color_map</tt> for
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the graph.
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</blockquote>
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UTIL: <tt>buffer(Buffer& Q)</tt>
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<blockquote>
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The queue used to determine the order in which vertices will be
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discovered. If a FIFO queue is used, then the traversal will
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be according to the usual BFS ordering. Other types of queues
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can be used, but the traversal order will be different.
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For example Dijkstra's algorithm can be implemented
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using a priority queue. The type <tt>Buffer</tt> must be a model of
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<a href="./Buffer.html">Buffer</a>.<br>
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<b>Default:</b> <tt>boost::queue</tt><br>
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<b>Python</b>: The buffer must derive from the <a
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href="./Buffer.html">Buffer</a> type for the graph.
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</blockquote>
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<H3><A NAME="SECTION001330300000000000000">
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Complexity</A>
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</H3>
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<P>
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The time complexity is <i>O(E)</i>.
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<P>
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<h3>Visitor Event Points</h3>
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<ul>
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<li><b><tt>vis.examine_vertex(u, g)</tt></b>r is invoked in each
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vertex as it is removed from the queue.
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<li><b><tt>vis.examine_edge(e, g)</tt></b> is invoked on every out-edge
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of each vertex immediately after the vertex is removed from the queue.
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<li><b><tt>vis.tree_edge(e, g)</tt></b> is invoked (in addition to
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<tt>examine_edge()</tt>) if the edge is a tree edge. The
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target vertex of edge <tt>e</tt> is discovered at this time.
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<li><b><tt>vis.discover_vertex(u, g)</tt></b> is invoked the first time the
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algorithm encounters vertex <i>u</i>. All vertices closer to the
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source vertex have been discovered, and vertices further from the
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source have not yet been discovered.
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<li><b><tt>vis.non_tree_edge(e, g)</tt></b> is invoked (in addition to
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<tt>examine_edge()</tt>) if the edge is not a tree edge.
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<li><b><tt>vis.gray_target(e, g)</tt></b> is invoked (in addition to
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<tt>non_tree_edge()</tt>) if the target vertex is colored gray at the
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time of examination. The color gray indicates that
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the vertex is currently in the queue.
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<li><b><tt>vis.black_target(e, g)</tt></b> is invoked (in addition to
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<tt>non_tree_edge()</tt>) if the target vertex is colored black at the
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time of examination. The color black indicates that the
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vertex is no longer in the queue.
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<li><b><tt>vis.finish_vertex(u, g)</tt></b> is invoked after all of the out
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edges of <i>u</i> have been examined and all of the adjacent vertices
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have been discovered.
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</ul>
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<h3>See Also</h3>
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<a href="./breadth_first_search.html"><tt>breadth_first_search()</tt></a>,
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<a href="./bfs_visitor.html"><tt>bfs_visitor</tt></a>, and
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<a href="./depth_first_search.html"><tt>depth_first_search()</tt></a>
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<h3>Notes</h3>
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<p><a name="1">[1]</a>
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Since the visitor parameter is passed by value, if your visitor
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contains state then any changes to the state during the algorithm
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will be made to a copy of the visitor object, not the visitor object
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passed in. Therefore you may want the visitor to hold this state by
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pointer or reference.
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<br>
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<HR>
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<TABLE>
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<TR valign=top>
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<TD nowrap>Copyright © 2000-2001</TD><TD>
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<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>)
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</TD></TR></TABLE>
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</BODY>
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</HTML>
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