Change value of adjacent vertices and remove self loop

Question

Try writing Kargers algorithm with boost :: graph

Example

(the first column is the vertex, the others are adjacent vertices):

• 1 2 3
• 2 1 3 4
• 3 1 2 4
• 4 2 3

Suppose I merge from 2 to 1, I get the result

• 1 2 3 2 1 1 3 4
• 2 1 3 4
• 3 1 2 4
• 4 2 3

first question: how do I change adjacent vertices (from "2" to "1") of vertex 1?

my naive decision

template<typename Vertex, typename Graph>
void change_adjacent_vertices_value(Vertex input, Vertex value, Graph &g)
{
    for (auto it = boost::adjacent_vertices(input, g);
         it.first != it.second; ++it.first){
        if(*it.first == value){
            *(it.first) = input; //error C2106: '=' : left operand must be l-value
        }
    }
}

Apparently, I cannot set the value of adjacent vertices to "1" in this way

The result I want after "change_adjacent_vertices_value"

• 1 1 3 1 1 1 3 4
• 2 1 3 4
• 3 1 2 4
• 4 2 3

second question: how could I pull adjacent peaks?

Suppose I want to infer sequential 1 from vertex 1 The result that I expected

• 1 1 3 1 3 4
• 2 1 3 4
• 3 1 2 4
• 4 2 3

"pop_adjacent_vertex" ?

Answer 1

, . , , , .

API Mutable Graph: http://www.boost.org/doc/libs/1_55_0/libs/graph/doc/MutableGraph.html

:

///adds all edges from src to target and removes the vertex src from the graph
template<typename Vertex, typename Graph>
void merge_vertices(Vertex src, Vertex tgt, Graph &g)
{
    for (auto it = boost::out_edges(src, g);
         it.first != it.second; ++it.first)
    {
        Vertex u = target(*it.first,g);
        add_edge(u,tgt,g); 
        //Note, if edges have properties, you should extract and copy them as well
    }
    clear_vertex(src,g);  //removes all edges to/from "src"
    remove_vertex(src,g); //removes vertex src itself
}

, , .

:

typedef boost::adjacency_list<boost::listS, 
         boost::listS, boost::undirectedS > graph_t;
typedef boost::graph_traits<graph_t>::vertex_descriptor vertex_t;

int main(int, char**)
{
    typedef std::map<vertex_t, size_t> IndexMap;
    IndexMap mapIndex;

    graph_t g;
    vertex_t v0 = add_vertex(g);
    mapIndex[v0]=0;
    vertex_t v1 = add_vertex(g);
    mapIndex[v1]=1;
    vertex_t v2 = add_vertex(g);
    mapIndex[v2]=2;
    vertex_t v3 = add_vertex(g);
    mapIndex[v3]=3;

    add_edge(v0,v2,g);
    add_edge(v1,v3,g);
    add_edge(v1,v0,g);
    std::cout << "Before merging " << std::endl;
    boost::print_graph(g, boost::make_assoc_property_map(mapIndex));

    merge_vertices(v1,v2,g);
    std::cout << "After merging "<< std::endl;

    boost::print_graph(g, boost::make_assoc_property_map(mapIndex));;
}

:

Before merging 
0 <--> 2 1 
1 <--> 3 0 
2 <--> 0 
3 <--> 1 
After merging 
0 <--> 2 2 
2 <--> 0 3 0 
3 <--> 2