# ConnectedComponents

VTKExamples/Cxx/Graphs/ConnectedComponents

### Description

This example constructs a graph with 4 vertices and 2 edges. V1 and V2 are not connected to V3 or V4. We wish to obtain all of the connected components of the graph. The output of the example is a list of component IDs. All vertices with the same ID can be reached from any vertex with the same ID.

### Code

ConnectedComponents.cxx

    #include <vtkSmartPointer.h>

    #include <vtkBoostConnectedComponents.h>
    #include <vtkDataArray.h>
    #include <vtkDataSetAttributes.h>
    #include <vtkGraph.h>
    #include <vtkIntArray.h>
    #include <vtkMutableUndirectedGraph.h>

    int main ( int, char *[] )
    {
      vtkSmartPointer<vtkMutableUndirectedGraph> g =
        vtkSmartPointer<vtkMutableUndirectedGraph>::New();

      vtkIdType v1 = g->AddVertex();
      vtkIdType v2 = g->AddVertex();
      vtkIdType v3 = g->AddVertex();
      vtkIdType v4 = g->AddVertex();

      g->AddEdge ( v1, v2 );
      g->AddEdge ( v3, v4 );

      vtkSmartPointer<vtkBoostConnectedComponents> connectedComponents =
        vtkSmartPointer<vtkBoostConnectedComponents>::New();
      connectedComponents->SetInput(g);
      connectedComponents->Update();

      vtkGraph* outputGraph = connectedComponents->GetOutput();

      vtkIntArray* components = vtkIntArray::SafeDownCast(
        outputGraph->GetVertexData()->GetArray("component"));

      for(vtkIdType i = 0; i < components->GetNumberOfTuples(); i++)
      {
        int val = components->GetValue(i);
        std::cout << val << std::endl;
      }

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(ConnectedComponents)

    find_package(VTK REQUIRED)
    include(${VTK_USE_FILE})

    add_executable(ConnectedComponents MACOSX_BUNDLE ConnectedComponents.cxx )

    target_link_libraries(ConnectedComponents ${VTK_LIBRARIES})

### Download and Build ConnectedComponents

Click here to download ConnectedComponents and its CMakeLists.txt file. Once the tarball ConnectedComponents.tar has been downloaded and extracted,

    cd ConnectedComponents/build

If VTK is installed:

    cmake ..

If VTK is not installed but compiled on your system, you will need to specify the path to your VTK build:

    cmake -DVTK_DIR:PATH=/home/me/vtk_build ..

Build the project:

    make

and run it:

    ./ConnectedComponents

WINDOWS USERS

Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.