source: lemon-0.x/src/include/dijkstra.h @ 296:09d6d48815a5

// -*- C++ -*-

/* 
 *template <Graph, T, Heap=FibHeap, LengthMap=Graph::EdgeMap<T> >
 *
 *Constructor: 
 *
 *Dijkstra(Graph G, LengthMap length)
 *
 *
 *Methods:
 *
 *void run(Node s)
 *
 *T dist(Node v) : After run(s) was run, it returns the distance from s to v. 
 *   Returns T() if v is not reachable from s.
 *
 *Edge pred(Node v) : After run(s) was run, it returns the last 
 *   edge of a shortest s-v path. It is INVALID for s and for 
 *   the nodes not reachable from s.
 *
 *bool reached(Node v) : After run(s) was run, it is true iff v is 
 *   reachable from s
 *
 */

#ifndef HUGO_DIJKSTRA_H
#define HUGO_DIJKSTRA_H

///\file
///\brief Dijkstra algorithm.

#include <fib_heap.h>
#include <bin_heap.h>
#include <invalid.h>

namespace hugo {
  
  //Alpar: Changed the order of the parameters
  
  ///%Dijkstra algorithm class.

  ///This class provides an efficient implementation of %Dijkstra algorithm.
  ///The edge lengths are passed to the algorithm using a
  ///\ref ReadMapSkeleton "readable map",
  ///so it is easy to change it to any kind of length.
  ///
  ///The type of the length is determined by the \c ValueType of the length map.
  ///
  ///It is also possible to change the underlying priority heap.
  ///
  ///\param Graph The graph type the algorithm runs on.
  ///\param LengthMap This read-only
  ///EdgeMap
  ///determines the
  ///lengths of the edges. It is read once for each edge, so the map
  ///may involve in relatively time consuming process to compute the edge
  ///length if it is necessary. The default map type is
  ///\ref GraphSkeleton::EdgeMap "Graph::EdgeMap<int>"
  ///\param Heap The heap type used by the %Dijkstra
  ///algorithm. The default
  ///is using \ref BinHeap "binary heap".
  
#ifdef DOXYGEN
  template <typename Graph,
            typename LengthMap,
            typename Heap>
#else
  template <typename Graph,
            typename LengthMap=typename Graph::EdgeMap<int>,
            template <class,class,class> class Heap = BinHeap >
#endif
  class Dijkstra{
  public:
    typedef typename Graph::Node Node;
    typedef typename Graph::NodeIt NodeIt;
    typedef typename Graph::Edge Edge;
    typedef typename Graph::OutEdgeIt OutEdgeIt;
    
    typedef typename LengthMap::ValueType ValueType;
    typedef typename Graph::NodeMap<Edge> PredMap;
    typedef typename Graph::NodeMap<Node> PredNodeMap;
    typedef typename Graph::NodeMap<ValueType> DistMap;

  private:
    const Graph& G;
    const LengthMap& length;
    PredMap predecessor;
    PredNodeMap pred_node;
    DistMap distance;
    
  public :
    
    Dijkstra(Graph& _G, LengthMap& _length) :
      G(_G), length(_length), predecessor(_G), pred_node(_G), distance(_G) { }
    
    void run(Node s);
    
    ///The distance of a node from the source.

    ///Returns the distance of a node from the source.
    ///\pre \ref run() must be called before using this function.
    ///\warning If node \c v in unreachable from the source the return value
    ///of this funcion is undefined.
    ValueType dist(Node v) const { return distance[v]; }
    ///Returns the edges of the shortest path tree.

    ///For a node \c v it returns the last edge of the shortest path
    ///from the source to \c v or INVALID if \c v is unreachable
    ///from the source.
    ///\pre \ref run() must be called before using this function.
    Edge pred(Node v) const { return predecessor[v]; }
    ///Returns the nodes of the shortest paths.

    ///For a node \c v it returns the last but one node of the shortest path
    ///from the source to \c v or INVALID if \c v is unreachable
    ///from the source.
    ///\pre \ref run() must be called before using this function.
    Node predNode(Node v) const { return pred_node[v]; }
    
    ///Returns a reference to the NodeMap of distances.

    ///\pre \ref run() must be called before using this function.
    ///
    const DistMap &distMap() const { return distance;}
    ///Returns a reference to the shortest path tree map.

    ///Returns a reference to the NodeMap of the edges of the
    ///shortest path tree.
    ///\pre \ref run() must be called before using this function.
    const PredMap &predMap() const { return predecessor;}
    ///Returns a reference to the map of nodes of  shortest paths.

    ///Returns a reference to the NodeMap of the last but one nodes of the
    ///shortest paths.
    ///\pre \ref run() must be called before using this function.
    const PredNodeMap &predNodeMap() const { return pred_node;}

    ///Checks if a node is reachable from the source.

    ///Returns \c true if \c v is reachable from the source.
    ///\warning the source node is reported to be unreached!
    ///\todo Is this what we want?
    ///\pre \ref run() must be called before using this function.
    ///
    bool reached(Node v) { return G.valid(predecessor[v]); }
    
  };
  

  // **********************************************************************
  //  IMPLEMENTATIONS
  // **********************************************************************

  ///Runs %Dijkstra algorithm from node the source.

  ///This method runs the %Dijkstra algorithm from a source node \c s
  ///in order to
  ///compute the
  ///shortest path to each node. The algorithm computes
  ///- The shortest path tree.
  ///- The distance of each node from the source.
  template <typename Graph, typename LengthMap,
            template<class,class,class> class Heap >
  void Dijkstra<Graph,LengthMap,Heap>::run(Node s) {
    
    NodeIt u;
    for ( G.first(u) ; G.valid(u) ; G.next(u) ) {
      predecessor.set(u,INVALID);
      pred_node.set(u,INVALID);
      // If a node is unreacheable, then why should be the dist=0?
      // distance.set(u,0);
      //      reach.set(u,false);
    }
    
    typename Graph::NodeMap<int> heap_map(G,-1);
    
    Heap<Node,ValueType,typename Graph::NodeMap<int> > heap(heap_map);
    
    heap.push(s,0); 
    
      while ( !heap.empty() ) {
        
        Node v=heap.top(); 
        ValueType oldvalue=heap[v];
        heap.pop();
        distance.set(v, oldvalue);
        
        for(OutEdgeIt e = G.template first<OutEdgeIt>(v);
            G.valid(e); G.next(e)) {
          Node w=G.head(e); 
          
          switch(heap.state(w)) {
          case heap.PRE_HEAP:
            heap.push(w,oldvalue+length[e]); 
            predecessor.set(w,e);
            pred_node.set(w,v);
            break;
          case heap.IN_HEAP:
            if ( oldvalue+length[e] < heap[w] ) {
              heap.decrease(w, oldvalue+length[e]); 
              predecessor.set(w,e);
              pred_node.set(w,v);
            }
            break;
          case heap.POST_HEAP:
            break;
          }
        }
      }
  }
  
} //END OF NAMESPACE HUGO

#endif