kruskal_demo.cc File Reference

---

Detailed Description

This demo program shows how to find a minimum weight spanning tree in a graph by using the Kruskal algorithm.

/* -*- C++ -*-
 *
 * This file is a part of LEMON, a generic C++ optimization library
 *
 * Copyright (C) 2003-2008
 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
 * (Egervary Research Group on Combinatorial Optimization, EGRES).
 *
 * Permission to use, modify and distribute this software is granted
 * provided that this copyright notice appears in all copies. For
 * precise terms see the accompanying LICENSE file.
 *
 * This software is provided "AS IS" with no warranty of any kind,
 * express or implied, and with no claim as to its suitability for any
 * purpose.
 *
 */


#include <iostream>
#include <vector>

#include <lemon/maps.h>
#include <lemon/kruskal.h>
#include <lemon/list_graph.h>


using namespace std;
using namespace lemon;


int main() {

  typedef ListGraph::Node Node;
  typedef ListGraph::Edge Edge;
  typedef ListGraph::NodeIt NodeIt;
  typedef ListGraph::EdgeIt EdgeIt;

  ListGraph g;
  //Make an example graph g.
  Node s=g.addNode();
  Node v1=g.addNode();
  Node v2=g.addNode();
  Node v3=g.addNode();
  Node v4=g.addNode();
  Node t=g.addNode();
  
  Edge e1 = g.addEdge(s, v1);
  Edge e2 = g.addEdge(s, v2);
  Edge e3 = g.addEdge(v1, v2);
  Edge e4 = g.addEdge(v2, v1);
  Edge e5 = g.addEdge(v1, v3);
  Edge e6 = g.addEdge(v3, v2);
  Edge e7 = g.addEdge(v2, v4);
  Edge e8 = g.addEdge(v4, v3);
  Edge e9 = g.addEdge(v3, t);
  Edge e10 = g.addEdge(v4, t);

  //Make the input for the kruskal.
  typedef ListGraph::EdgeMap<int> ECostMap;
  ECostMap edge_cost_map(g);

  // Fill the edge_cost_map. 
  edge_cost_map.set(e1, -10);
  edge_cost_map.set(e2, -9);
  edge_cost_map.set(e3, -8);
  edge_cost_map.set(e4, -7);
  edge_cost_map.set(e5, -6);
  edge_cost_map.set(e6, -5);
  edge_cost_map.set(e7, -4);
  edge_cost_map.set(e8, -3);
  edge_cost_map.set(e9, -2);
  edge_cost_map.set(e10, -1);

  // Make the map or the vector, which will contain the edges of the minimum
  // spanning tree.

  typedef ListGraph::EdgeMap<bool> EBoolMap;
  EBoolMap tree_map(g);

  vector<Edge> tree_edge_vec;


  //Kruskal Algorithm.  

  //Input: a graph (g); a costmap of the graph (edge_cost_map); a
  //boolmap (tree_map) or a vector (tree_edge_vec) to store the edges
  //of the output tree;

  //Output: it gives back the value of the minimum spanning tree, and
  //set true for the edges of the tree in the edgemap tree_map or
  //store the edges of the tree in the vector tree_edge_vec;


  // Kruskal with boolmap;
  std::cout << "The weight of the minimum spanning tree is " << 
    kruskal(g, edge_cost_map, tree_map)<<std::endl;

  int k=0;
  std::cout << "The edges of the tree:" ;
  for(EdgeIt i(g); i!=INVALID; ++i)
    if (tree_map[i]) { 
      std::cout << g.id(i) <<";";
      ++k;
    }

  std::cout << std::endl;
  std::cout << "The size of the tree is: "<< k << std::endl;


  // Kruskal with vector;
  std::cout << "The weight of the minimum spanning tree again is " << 
    kruskal(g, edge_cost_map, std::back_inserter(tree_edge_vec)) <<std::endl;



  std::cout << "The edges of the tree again: " ;
  for(int i=tree_edge_vec.size()-1; i>=0;  i--)
    std::cout << g.id(tree_edge_vec[i]) << ";" ;
  std::cout << std::endl;
  std::cout << "The size of the tree again is: "<< tree_edge_vec.size()
            << std::endl; 

  
  return 0;
}

#include <iostream>
#include <vector>
#include <lemon/maps.h>
#include <lemon/kruskal.h>
#include <lemon/list_graph.h>