alpar@2391: /* -*- C++ -*- alpar@2391: * alpar@2391: * This file is a part of LEMON, a generic C++ optimization library alpar@2391: * alpar@2391: * Copyright (C) 2003-2007 alpar@2391: * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport alpar@2391: * (Egervary Research Group on Combinatorial Optimization, EGRES). alpar@2391: * alpar@2391: * Permission to use, modify and distribute this software is granted alpar@2391: * provided that this copyright notice appears in all copies. For alpar@2391: * precise terms see the accompanying LICENSE file. alpar@2391: * alpar@2391: * This software is provided "AS IS" with no warranty of any kind, alpar@2391: * express or implied, and with no claim as to its suitability for any alpar@2391: * purpose. alpar@2391: * alpar@2391: */ alpar@2391: alpar@2216: namespace lemon { alpar@2196: /** alpar@2196: \page algorithms Algorithms alpar@2196: alpar@2216: \section algo_bfs_dfs Bfs/Dfs alpar@2216: Both \ref lemon::Bfs "Bfs" and \ref lemon::Dfs "Dfs" are highly adaptable and efficient alpar@2216: implementations of the well known algorithms. The algorithms are placed most cases in alpar@2216: separated files named after the algorithm itself but lower case as all other header file names. alpar@2216: For example the next Bfs class is in the \c lemon/bfs.h. alpar@2216: alpar@2216: \subsection Bfs alpar@2216: The algorithm is implemented in the \ref lemon::Bfs "Bfs" template class - rather than as function. alpar@2216: The class has two template parameters: \b GR and \TR.
alpar@2216: GR is the graph the algorithm runs on. It has \ref lemon::ListGraph "ListGraph" as default type. alpar@2216: TR is a Traits class commonly used to easy the parametrization of templates. In most cases you alpar@2216: wont need to modify the default type \ref lemon::BfsDefaultTraits "BfsDefaultTraits". alpar@2216: alpar@2216: To use the class, declare it! alpar@2216: \code alpar@2216: Bfs bfs(gr); alpar@2216: \endcode alpar@2216: Note the lack of second template argument because of the default parameter. alpar@2216: alpar@2216: It provides a simple but powerful interface to control the execution. alpar@2216: \code alpar@2216: int dist = bfs.run(s,t); alpar@2216: \endcode alpar@2216: It finds the shortest path from node \c s to node \c t and returns it, or zero alpar@2216: if there is no path from \c s to \c t.
alpar@2216: If you want the shortest path from a specified node to all other node, just write: alpar@2216: \code alpar@2216: bfs.run(s); alpar@2216: \endcode alpar@2216: Now the distances and path information are stored in maps which you can access with alpar@2216: member functions like \ref lemon::Bfs::distMap "distMap()" or \ref lemon::Bfs::predMap "predMap()".
alpar@2216: Or more directly whit other member functions like \c predNode(). Once the algorithm alpar@2216: is finished (or to be precise reached that node) \ref lemon::Bfs::dist "dist()" or \ref lemon::Bfs::predNode alpar@2216: "predNode()" can be called. alpar@2216: alpar@2216: For an example let's say we want to print the shortest path of those nodes which alpar@2216: are in a certain distance. alpar@2216: \code alpar@2216: bfs.run(s); alpar@2216: alpar@2216: for( ListUGraph::NodeIt n(gr); n != INVALID; ++n ) { alpar@2216: if( bfs.reached(n) && bfs.dist(n) <= max_dist ) { alpar@2216: std::cout << gr.id(n); alpar@2216: alpar@2216: Node prev = bfs.prevNode(n); alpar@2216: while( prev != INVALID ) { alpar@2216: std::cout << "<-" << gr.id(prev); alpar@2216: prev = bfs.prevNode(n); alpar@2216: } alpar@2216: alpar@2216: std::cout << std::endl; alpar@2216: } alpar@2216: } alpar@2216: \endcode alpar@2216: alpar@2216: \subsubsection bfs_adv_control Advanced control alpar@2216: In the previous code we only used \c run(). Now we introduce the way you can directly alpar@2216: control the execution of the algorithm. alpar@2216: alpar@2216: First you have to initialize the variables with \ref lemon::Bfs::init "init()". alpar@2216: \code alpar@2216: bfs.init(); alpar@2216: \endcode alpar@2216: alpar@2216: Then you add one or more source nodes to the queue. They will be processed, as they would alpar@2216: be reached by the algorithm before. And yes - you can add more sources during the execution. alpar@2216: \code alpar@2216: bfs.addSource(node_1); alpar@2216: bfs.addSource(node_2); alpar@2216: ... alpar@2216: \endcode alpar@2216: alpar@2216: And finally you can start the process with \ref lemon::Bfs::start "start()", or alpar@2216: you can write your own loop to process the nodes one-by-one. alpar@2216: alpar@2216: \todo demo for bfs advanced control alpar@2216: alpar@2216: \subsection Dfs alpar@2216: Since Dfs is very similar to Bfs with a few tiny differences we only see a bit more complex example alpar@2216: to demonstrate Dfs's capabilities. alpar@2216: alpar@2216: We will see a program, which solves the problem of topological ordering. alpar@2216: We need to know in which order we should put on our clothes. The program will do the following: alpar@2216:
    alpar@2216:
  1. We run the dfs algorithm to all nodes. alpar@2216:
  2. Put every node into a list when processed completely. alpar@2216:
  3. Write out the list in reverse order. alpar@2216:
alpar@2216: alpar@2216: \dontinclude topological_ordering.cc alpar@2216: First of all we will need an own \ref lemon::Dfs::ProcessedMap "ProcessedMap". The ordering alpar@2216: will be done through it. mqrelly@2281: \skip MyOrdererMap alpar@2216: \until }; alpar@2216: The class meets the \ref lemon::WriteMap "WriteMap" concept. In it's \c set() method the only thing alpar@2216: we need to do is insert the key - that is the node who's processing just finished - into the beginning mqrelly@2281: of the list.
mqrelly@2281: Although we implemented this needed helper class ourselves it was not necessary. mqrelly@2281: The \ref lemon::FrontInserterBoolMap "FrontInserterBoolMap" class does exactly mqrelly@2281: what we needed. To be correct it's more general - and it's all in \c LEMON. But mqrelly@2281: we wanted to show you, how easy is to add additional functionality. alpar@2216: alpar@2216: First we declare the needed data structures: the graph and a map to store the nodes' label. alpar@2216: \skip ListGraph alpar@2216: \until label alpar@2216: alpar@2216: Now we build a graph. But keep in mind that it must be DAG because cyclic graphs has no topological alpar@2216: ordering. alpar@2216: \skip belt alpar@2216: \until trousers alpar@2216: We label them... alpar@2216: \skip label alpar@2216: \until trousers alpar@2216: Then add directed edges which represent the precedences between those items. alpar@2216: \skip trousers, belt alpar@2216: \until ); alpar@2216: alpar@2216: See how easy is to access the internal information of this algorithm trough maps. alpar@2216: We only need to set our own map as the class's \ref lemon::Dfs::ProcessedMap "ProcessedMap". alpar@2216: \skip Dfs alpar@2216: \until run alpar@2216: alpar@2216: And now comes the third part. Write out the list in reverse order. But the list was alpar@2216: composed in reverse way (with \c push_front() instead of \c push_back() so we just iterate it. alpar@2216: \skip std alpar@2216: \until endl alpar@2216: alpar@2216: The program is to be found in the \ref demo directory: \ref topological_ordering.cc mqrelly@2281: mqrelly@2281: More algorithms are described in the \ref algorithms2 "second part". alpar@2196: */ alpar@2216: }