stronglyConnectedComponents - SeqAn API Documentation

# fn() stronglyConnectedComponents
Decomposes a directed graph into its strongly connected components.

Defined in | <seqan/graph_algorithms.h>
Signature | `TSize stronglyConnectedComponents(components, g);`

## Parameters

`components` | A property map.Each vertex is mapped to a component id. If two vertices share the same id they are in the same component.
`g` | A directed graph. Types: Directed Graph

## Return Values

`TSize` | Number of strongly connected components, Size type of g.

## Detailed Description

### Example

    #include <iostream>
    #include <seqan/graph_algorithms.h>

    using namespace seqan;

    int main()
    {
        typedef Graph<Directed<> > TGraph;
        typedef VertexDescriptor<TGraph>::Type TVertexDescriptor;
        typedef Size<TGraph>::Type TSize;

        // Create grap with 14 directed edges (1,0), (0,4), ...
        TSize numEdges = 14;
        TVertexDescriptor edges[] = {1, 0, 0, 4, 2, 1, 4, 1, 5, 1, 6, 2, 3, 2, 2, 3, 7, 3, 5, 4, 6, 5, 5, 6, 7, 6, 7, 7};
        TGraph g;
        addEdges(g, edges, numEdges);
        // Print graph.
        std::cout << g << std::endl;

        // Create external property map with vertex names and assign to graph.
        String<char> nameMap;
        char names[] = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'};
        assignVertexMap(nameMap, g, names);

        // Compute strongly connected components.
        String<unsigned int> component;
        stronglyConnectedComponents(component, g);

        // Print result to stdout.
        std::cout << "Strongly Connected Components: \n";
        typedef Iterator<TGraph, VertexIterator>::Type TVertexIterator;
        TVertexIterator it(g);
        while (!atEnd(it))
        {
            std::cout << "Vertex " << getProperty(nameMap, getValue(it)) << ": \n"
                      << "Component = " << getProperty(component, getValue(it)) << "\n";
            goNext(it);
        }

        return 0;
    }

Demo: demos/dox/graph_algorithms/strongly_connected_components.cpp

    Adjacency list:
    0 -> 4,
    1 -> 0,
    2 -> 3,1,
    3 -> 2,
    4 -> 1,
    5 -> 6,4,1,
    6 -> 5,2,
    7 -> 7,6,3,
    Edge list:
    Source: 0,Target: 4 (Id: 1)
    Source: 1,Target: 0 (Id: 0)
    Source: 2,Target: 3 (Id: 7)
    Source: 2,Target: 1 (Id: 2)
    Source: 3,Target: 2 (Id: 6)
    Source: 4,Target: 1 (Id: 3)
    Source: 5,Target: 6 (Id: 11)
    Source: 5,Target: 4 (Id: 9)
    Source: 5,Target: 1 (Id: 4)
    Source: 6,Target: 5 (Id: 10)
    Source: 6,Target: 2 (Id: 5)
    Source: 7,Target: 7 (Id: 13)
    Source: 7,Target: 6 (Id: 12)
    Source: 7,Target: 3 (Id: 8)

    Strongly Connected Components:
    Vertex a:
    Component = 3
    Vertex b:
    Component = 3
    Vertex c:
    Component = 2
    Vertex d:
    Component = 2
    Vertex e:
    Component = 3
    Vertex f:
    Component = 1
    Vertex g:
    Component = 1
    Vertex h:
    Component = 0

## Data Races

If not stated otherwise, concurrent invocation is not guaranteed to be thread-safe.

#### Dox Sources

    /*!
     * @fn stronglyConnectedComponents
     *
     * @headerfile <seqan/graph_algorithms.h>
     *
     * @brief Decomposes a directed graph into its strongly connected components.
     *
     * @signature TSize stronglyConnectedComponents(components, g);
     *
     * @param[out] components  A property map.Each vertex is mapped to a component
     *                        id. If two vertices share the same id they are in the
     *                        same component.
     * @param[in] g A directed graph. Types: Directed Graph
     *
     * @return TSize Number of strongly connected components, Size type of g.
     *
     * @section Example
     *
     * @include demos/dox/graph_algorithms/strongly_connected_components.cpp
     *
     * @include demos/dox/graph_algorithms/strongly_connected_components.cpp.stdout
     */