source: lemon-0.x/src/work/athos/preflow_push.hh @ 52:a4fc9c5dcee5

#ifndef PREFLOW_PUSH_HH
#define PREFLOW_PUSH_HH

#include <algorithm>
#include <list>
#include <vector>
//#include "pf_hiba.hh"
//#include <marci_list_graph.hh>
#include <marci_graph_traits.hh>
#include "reverse_bfs.hh"

using namespace std;

namespace marci {

  template <typename graph_type, typename T>
  class preflow_push {

    //Hasznos typedef-ek
    typedef graph_traits<graph_type>::node_iterator node_iterator;
    typedef graph_traits<graph_type>::edge_iterator edge_iterator;
    typedef graph_traits<graph_type>::each_node_iterator each_node_iterator;
    typedef graph_traits<graph_type>::each_edge_iterator each_edge_iterator;
    typedef graph_traits<graph_type>::out_edge_iterator out_edge_iterator;
    typedef graph_traits<graph_type>::in_edge_iterator in_edge_iterator;
    typedef graph_traits<graph_type>::sym_edge_iterator sym_edge_iterator;

    //---------------------------------------------
    //Parameters of the algorithm
    //---------------------------------------------
    //Fully examine an active node until excess becomes 0
    enum node_examination_t {examine_full, examine_to_relabel};
    //No more implemented yet:, examine_only_one_edge};
    node_examination_t node_examination;
    //Which implementation to be used
    enum implementation_t {impl_fifo, impl_highest_label};
    //No more implemented yet:};
    implementation_t implementation;
    //---------------------------------------------
    //Parameters of the algorithm
    //---------------------------------------------
 
  private:
    //input
    graph_type& G;
    node_iterator s;
    node_iterator t;
    edge_property_vector<graph_type, T> &capacity;
    //output
    edge_property_vector<graph_type, T> preflow;
    T maxflow_value;
  
    //auxiliary variables for computation
    int number_of_nodes;
    node_property_vector<graph_type, int> level;
    node_property_vector<graph_type, T> excess;
    
    //Number of nodes on each level
    vector<int> num_of_nodes_on_level;
    
    //For the FIFO implementation
    list<node_iterator> fifo_nodes;
    //For 'highest label' implementation
    int highest_active;
    //int second_highest_active;
    vector< list<node_iterator> > active_nodes;

  public:
  
    //Constructing the object using the graph, source, sink and capacity vector
    preflow_push(
                      graph_type& _G, 
                      node_iterator _s, 
                      node_iterator _t, 
                      edge_property_vector<graph_type, T>& _capacity)
      : G(_G), s(_s), t(_t), 
        capacity(_capacity), 
        preflow(_G),
        //Counting the number of nodes
        number_of_nodes(number_of(G.first_node())),
        level(_G),
        excess(_G)//,
        // Default constructor: active_nodes()
    { 
      //Simplest parameter settings
      node_examination = examine_full;//examine_to_relabel;//
      //Which implementation to be usedexamine_full
      implementation = impl_highest_label;//impl_fifo;
 
      //
      num_of_nodes_on_level.resize(2*number_of_nodes-1);
      num_of_nodes_on_level.clear();

      switch(implementation){
      case impl_highest_label :{
        active_nodes.resize(2*number_of_nodes-1);
        active_nodes.clear();
        break;
      }
      default:
        break;
      }

    }

    //Returns the value of a maximal flow 
    T run();
  
    edge_property_vector<graph_type, T> getmaxflow(){
      return preflow;
    }


  private:
    //For testing purposes only
    //Lists the node_properties
    void write_property_vector(node_property_vector<graph_type, T> a, 
                               char* prop_name="property"){
      for(each_node_iterator i=G.first_node(); i.valid(); ++i) {
        cout<<"Node id.: "<<G.id(i)<<", "<<prop_name<<" value: "<<a.get(i)<<endl;
      }
      cout<<endl;
    }

    //Modifies the excess of the node and makes sufficient changes
    void modify_excess(const node_iterator& a ,T v){
        T old_value=excess.get(a);
        excess.put(a,old_value+v);
    }
  
    //This private procedure is supposed to modify the preflow on edge j
    //by value v (which can be positive or negative as well) 
    //and maintain the excess on the head and tail
    //Here we do not check whether this is possible or not
    void modify_preflow(edge_iterator j, const T& v){

      //Auxiliary variable
      T old_value;
        
      //Modifiyng the edge
      old_value=preflow.get(j);
      preflow.put(j,old_value+v);


      //Modifiyng the head
      modify_excess(G.head(j),v);
        
      //Modifiyng the tail
      modify_excess(G.tail(j),-v);

    }

    //Gives the active node to work with 
    //(depending on the implementation to be used)
    node_iterator get_active_node(){
      //cout<<highest_active<<endl;

      switch(implementation) {
      case impl_highest_label : {

        //First need to find the highest label for which there"s an active node
        while( highest_active>=0 && active_nodes[highest_active].empty() ){ 
          --highest_active;
        }

        if( highest_active>=0) {
          node_iterator a=active_nodes[highest_active].front();
          active_nodes[highest_active].pop_front();
          return a;
        }
        else {
          return node_iterator();
        }
        
        break;
        
      }
      case impl_fifo : {

        if( ! fifo_nodes.empty() ) {
          node_iterator a=fifo_nodes.front();
          fifo_nodes.pop_front();
          return a;
        }
        else {
          return node_iterator();
        }
        break;
      }
      }
      //
      return node_iterator();
    }

    //Puts node 'a' among the active nodes
    void make_active(const node_iterator& a){
      //s and t never become active
      if (a!=s && a!= t){
        switch(implementation){
        case impl_highest_label :
          active_nodes[level.get(a)].push_back(a);
          break;
        case impl_fifo :
          fifo_nodes.push_back(a);
          break;
        }

      }

      //Update highest_active label
      if (highest_active<level.get(a)){
        highest_active=level.get(a);
      }

    }

    //Changes the level of node a and make sufficent changes
    void change_level_to(node_iterator a, int new_value){
      int seged = level.get(a);
      level.put(a,new_value);
      --num_of_nodes_on_level[seged];
      ++num_of_nodes_on_level[new_value];
    }

    //Collection of things useful (or necessary) to do before running
    void preprocess(){

      //---------------------------------------
      //Initialize parameters
      //---------------------------------------

      //Setting starting preflow, level and excess values to zero
      //This can be important, if the algorithm is run more then once
      for(each_node_iterator i=G.first_node(); i.valid(); ++i) {
        level.put(i,0);
        excess.put(i,0);
        for(out_edge_iterator j=G.first_out_edge(i); j.valid(); ++j) 
          preflow.put(j, 0);
      }
      num_of_nodes_on_level[0]=number_of_nodes;
      highest_active=0;
      //---------------------------------------
      //Initialize parameters
      //---------------------------------------

      
      //------------------------------------
      //This is the only part that uses BFS
      //------------------------------------
      //Setting starting level values using reverse bfs
      reverse_bfs<graph_type> rev_bfs(G,t);
      rev_bfs.run();
      //write_property_vector(rev_bfs.dist,"rev_bfs");
      for(each_node_iterator i=G.first_node(); i.valid(); ++i) {
        change_level_to(i,rev_bfs.dist(i));
        //level.put(i,rev_bfs.dist.get(i));
      }
      //------------------------------------
      //This is the only part that uses BFS
      //------------------------------------
      
      
      //Starting level of s
      change_level_to(s,number_of_nodes);
      //level.put(s,number_of_nodes);
      
      
      //we push as much preflow from s as possible to start with
      for(out_edge_iterator j=G.first_out_edge(s); j.valid(); ++j){ 
        modify_preflow(j,capacity.get(j) );
        make_active(G.head(j));
        int lev=level.get(G.head(j));
        if(highest_active<lev){
          highest_active=lev;
        }
      }
      //cout<<highest_active<<endl;
    } 

    
    //If the preflow is less than the capacity on the given edge
    //then it is an edge in the residual graph
    bool is_admissible_forward_edge(out_edge_iterator j, int& new_level){
      if (capacity.get(j)>preflow.get(j)){
        if(level.get(G.tail(j))==level.get(G.head(j))+1){
          return true;
        }
        else{
          if (level.get(G.head(j)) < new_level)
            new_level=level.get(G.head(j));
        }
      }
      return false;
    }

    //If the preflow is greater than 0 on the given edge
    //then the edge reversd is an edge in the residual graph
    bool is_admissible_backward_edge(in_edge_iterator j, int& new_level){
      if (0<preflow.get(j)){
        if(level.get(G.tail(j))==level.get(G.head(j))-1){
          return true;
        }
        else{
          if (level.get(G.tail(j)) < new_level)
            new_level=level.get(G.tail(j));
        }
        
      }
      return false;
    }

 
  };  //class preflow_push  

  template<typename graph_type, typename T>
    T preflow_push<graph_type, T>::run() {
    
    preprocess();
    
    T e,v;
    node_iterator a;
    while (a=get_active_node(), a.valid()){
      //cout<<G.id(a)<<endl;
      //write_property_vector(excess,"excess");
      //write_property_vector(level,"level");

      //Initial value for the new level for the active node we are dealing with
      int new_level=2*number_of_nodes;

      bool go_to_next_node=false;
      e = excess.get(a);
      while (!go_to_next_node){
        
        //Out edges from node a
        {
          out_edge_iterator j=G.first_out_edge(a);
          while (j.valid() && e){

            if (is_admissible_forward_edge(j,new_level)){
              v=min(e,capacity.get(j) - preflow.get(j));
              e -= v;
              //New node might become active
              if (excess.get(G.head(j))==0){
                make_active(G.head(j));
              }
              modify_preflow(j,v);
            }
            ++j;
          }
        }
        //In edges to node a
        {
          in_edge_iterator j=G.first_in_edge(a);
          while (j.valid() && e){
            if (is_admissible_backward_edge(j,new_level)){
              v=min(e,preflow.get(j));
              e -= v;
              //New node might become active
              if (excess.get(G.tail(j))==0){
                make_active(G.tail(j));
              }
              modify_preflow(j,-v);
            }
            ++j;
          }
        }

        //cout<<G.id(a)<<" "<<new_level<<endl;

        if (0==e){
          //Saturating push
          go_to_next_node=true;
        }
        else{//If there is still excess in node a

          //Level remains empty
          if (num_of_nodes_on_level[level.get(a)]==1){
            change_level_to(a,number_of_nodes);
            //go_to_next_node=True;
          }
          else{
            change_level_to(a,new_level+1);
            //increase_level(a);
          }

    
          

          switch(node_examination){
          case examine_to_relabel:
            make_active(a);

            go_to_next_node = true;
            break;
          default:
            break;
          }
          
    
        
        }//if (0==e)
      }
    }
    maxflow_value = excess.get(t);
    return maxflow_value;
  }//run


}//namespace marci

#endif //PREFLOW_PUSH_HH