deba@2382: /* -*- C++ -*- deba@2382: * deba@2382: * This file is a part of LEMON, a generic C++ optimization library deba@2382: * deba@2382: * Copyright (C) 2003-2006 deba@2382: * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport deba@2382: * (Egervary Research Group on Combinatorial Optimization, EGRES). deba@2382: * deba@2382: * Permission to use, modify and distribute this software is granted deba@2382: * provided that this copyright notice appears in all copies. For deba@2382: * precise terms see the accompanying LICENSE file. deba@2382: * deba@2382: * This software is provided "AS IS" with no warranty of any kind, deba@2382: * express or implied, and with no claim as to its suitability for any deba@2382: * purpose. deba@2382: * deba@2382: */ deba@2382: deba@2382: #ifndef LEMON_STEINER_H deba@2382: #define LEMON_STEINER_H deba@2382: deba@2382: ///\ingroup approx deba@2382: ///\file deba@2382: ///\brief Algorithm for the 2-approximation of Steiner Tree problem. deba@2382: /// deba@2382: deba@2382: #include deba@2382: #include deba@2382: #include deba@2382: deba@2382: #include deba@2382: #include deba@2382: deba@2382: #include deba@2382: #include deba@2382: deba@2382: deba@2382: namespace lemon { deba@2382: deba@2382: /// \ingroup approx deba@2382: deba@2382: /// \brief Algorithm for the 2-approximation of Steiner Tree problem deba@2382: /// deba@2382: /// The Steiner-tree problem is the next: Given a connected deba@2382: /// undirected graph, a cost function on the edges and a subset of deba@2382: /// the nodes. Construct a tree with minimum cost which covers the deba@2382: /// given subset of the nodes. The problem is NP-hard moreover deba@2382: /// it is APX-complete too. deba@2382: /// deba@2382: /// Mehlhorn's approximation algorithm is implemented in this class, deba@2382: /// which gives a 2-approximation for the Steiner-tree problem. The deba@2382: /// algorithm's time complexity is O(nlog(n)+e). deba@2382: template > deba@2382: class SteinerTree { deba@2382: public: deba@2382: deba@2382: UGRAPH_TYPEDEFS(typename UGraph) deba@2382: deba@2382: typedef typename CostMap::Value Value; deba@2382: deba@2382: private: deba@2382: deba@2382: class CompMap { deba@2382: public: deba@2382: typedef Node Key; deba@2382: typedef Edge Value; deba@2382: deba@2382: private: deba@2382: const UGraph& _graph; deba@2382: typename UGraph::template NodeMap _comp; deba@2382: deba@2382: public: deba@2382: CompMap(const UGraph& graph) : _graph(graph), _comp(graph) {} deba@2382: deba@2382: void set(const Node& node, const Edge& edge) { deba@2382: if (edge != INVALID) { deba@2382: _comp.set(node, _comp[_graph.source(edge)]); deba@2382: } else { deba@2382: _comp.set(node, -1); deba@2382: } deba@2382: } deba@2382: deba@2382: int comp(const Node& node) const { return _comp[node]; } deba@2382: void comp(const Node& node, int value) { _comp.set(node, value); } deba@2382: }; deba@2382: deba@2382: typedef typename UGraph::template NodeMap PredMap; deba@2382: deba@2382: typedef ForkWriteMap ForkedMap; deba@2382: deba@2382: deba@2382: struct External { deba@2382: int source, target; deba@2382: UEdge uedge; deba@2382: Value value; deba@2382: deba@2382: External(int s, int t, const UEdge& e, const Value& v) deba@2382: : source(s), target(t), uedge(e), value(v) {} deba@2382: }; deba@2382: deba@2382: struct ExternalLess { deba@2382: bool operator()(const External& left, const External& right) const { deba@2382: return (left.source < right.source) || deba@2382: (left.source == right.source && left.target < right.target); deba@2382: } deba@2382: }; deba@2382: deba@2382: deba@2382: typedef typename UGraph::template NodeMap FilterMap; deba@2382: deba@2382: typedef typename UGraph::template UEdgeMap TreeMap; deba@2382: deba@2382: const UGraph& _graph; deba@2382: const CostMap& _cost; deba@2382: deba@2382: typename Dijkstra:: deba@2382: template DefPredMap::Create _dijkstra; deba@2382: deba@2382: PredMap* _pred; deba@2382: CompMap* _comp; deba@2382: ForkedMap* _forked; deba@2382: deba@2382: int _terminal_num; deba@2382: deba@2382: FilterMap *_filter; deba@2382: TreeMap *_tree; deba@2382: deba@2382: public: deba@2382: deba@2382: /// \brief Constructor deba@2382: deba@2382: /// Constructor deba@2382: /// deba@2382: SteinerTree(const UGraph &graph, const CostMap &cost) deba@2382: : _graph(graph), _cost(cost), _dijkstra(graph, _cost), deba@2382: _pred(0), _comp(0), _forked(0), _filter(0), _tree(0) {} deba@2382: deba@2382: /// \brief Initializes the internal data structures. deba@2382: /// deba@2382: /// Initializes the internal data structures. deba@2382: void init() { deba@2382: if (!_pred) _pred = new PredMap(_graph); deba@2382: if (!_comp) _comp = new CompMap(_graph); deba@2382: if (!_forked) _forked = new ForkedMap(*_pred, *_comp); deba@2382: if (!_filter) _filter = new FilterMap(_graph); deba@2382: if (!_tree) _tree = new TreeMap(_graph); deba@2382: _dijkstra.predMap(*_forked); deba@2382: _dijkstra.init(); deba@2382: _terminal_num = 0; deba@2382: for (NodeIt it(_graph); it != INVALID; ++it) { deba@2382: _filter->set(it, false); deba@2382: } deba@2382: } deba@2382: deba@2382: /// \brief Adds a new terminal node. deba@2382: /// deba@2382: /// Adds a new terminal node to the Steiner-tree problem. deba@2382: void addTerminal(const Node& node) { deba@2382: if (!_dijkstra.reached(node)) { deba@2382: _dijkstra.addSource(node); deba@2382: _comp->comp(node, _terminal_num); deba@2382: ++_terminal_num; deba@2382: } deba@2382: } deba@2382: deba@2382: /// \brief Executes the algorithm. deba@2382: /// deba@2382: /// Executes the algorithm. deba@2382: /// deba@2382: /// \pre init() must be called and at least some nodes should be deba@2382: /// added with addTerminal() before using this function. deba@2382: /// deba@2382: /// This method constructs an approximation of the Steiner-Tree. deba@2382: void start() { deba@2382: _dijkstra.start(); deba@2382: deba@2382: std::vector externals; deba@2382: for (UEdgeIt it(_graph); it != INVALID; ++it) { deba@2382: Node s = _graph.source(it); deba@2382: Node t = _graph.target(it); deba@2382: if (_comp->comp(s) == _comp->comp(t)) continue; deba@2382: deba@2382: Value cost = _dijkstra.dist(s) + _dijkstra.dist(t) + _cost[it]; deba@2382: deba@2382: if (_comp->comp(s) < _comp->comp(t)) { deba@2382: externals.push_back(External(_comp->comp(s), _comp->comp(t), deba@2382: it, cost)); deba@2382: } else { deba@2382: externals.push_back(External(_comp->comp(t), _comp->comp(s), deba@2382: it, cost)); deba@2382: } deba@2382: } deba@2382: std::sort(externals.begin(), externals.end(), ExternalLess()); deba@2382: deba@2382: SmartUGraph aux_graph; deba@2382: std::vector aux_nodes; deba@2382: deba@2382: for (int i = 0; i < _terminal_num; ++i) { deba@2382: aux_nodes.push_back(aux_graph.addNode()); deba@2382: } deba@2382: deba@2382: SmartUGraph::UEdgeMap aux_cost(aux_graph); deba@2382: SmartUGraph::UEdgeMap cross(aux_graph); deba@2382: { deba@2382: int i = 0; deba@2386: while (i < int(externals.size())) { deba@2382: int sn = externals[i].source; deba@2382: int tn = externals[i].target; deba@2382: Value ev = externals[i].value; deba@2382: UEdge ee = externals[i].uedge; deba@2382: ++i; deba@2386: while (i < int(externals.size()) && deba@2382: sn == externals[i].source && tn == externals[i].target) { deba@2382: if (externals[i].value < ev) { deba@2382: ev = externals[i].value; deba@2382: ee = externals[i].uedge; deba@2382: } deba@2382: ++i; deba@2382: } deba@2382: SmartUGraph::UEdge ne = deba@2382: aux_graph.addEdge(aux_nodes[sn], aux_nodes[tn]); deba@2382: aux_cost.set(ne, ev); deba@2382: cross.set(ne, ee); deba@2382: } deba@2382: } deba@2382: deba@2382: std::vector aux_tree_edges; deba@2382: BackInserterBoolMap > deba@2382: aux_tree_map(aux_tree_edges); deba@2382: prim(aux_graph, aux_cost, aux_tree_map); deba@2382: deba@2382: for (std::vector::iterator deba@2382: it = aux_tree_edges.begin(); it != aux_tree_edges.end(); ++it) { deba@2382: Node node; deba@2382: node = _graph.source(cross[*it]); deba@2382: while (node != INVALID && !(*_filter)[node]) { deba@2382: _filter->set(node, true); deba@2382: node = (*_pred)[node] != INVALID ? deba@2382: _graph.source((*_pred)[node]) : INVALID; deba@2382: } deba@2382: node = _graph.target(cross[*it]); deba@2382: while (node != INVALID && !(*_filter)[node]) { deba@2382: _filter->set(node, true); deba@2382: node = (*_pred)[node] != INVALID ? deba@2382: _graph.source((*_pred)[node]) : INVALID; deba@2382: } deba@2382: } deba@2382: deba@2382: prim(nodeSubUGraphAdaptor(_graph, *_filter), _cost, *_tree); deba@2382: deba@2382: } deba@2382: deba@2382: /// \brief Checks if an edge is in the Steiner-tree or not. deba@2382: /// deba@2382: /// Checks if an edge is in the Steiner-tree or not. deba@2382: /// \param e is the edge that will be checked deba@2382: /// \return \c true if e is in the Steiner-tree, \c false otherwise deba@2382: bool tree(UEdge e){ deba@2382: return (*_tree)[e]; deba@2382: } deba@2382: deba@2382: /// \brief Checks if the node is in the Steiner-tree or not. deba@2382: /// deba@2382: /// Checks if a node is in the Steiner-tree or not. deba@2382: /// \param n is the node that will be checked deba@2382: /// \return \c true if n is in the Steiner-tree, \c false otherwise deba@2382: bool tree(Node n){ deba@2382: return (*_filter)[n]; deba@2382: } deba@2382: deba@2382: deba@2382: }; deba@2382: deba@2382: } //END OF NAMESPACE LEMON deba@2382: deba@2382: #endif