dijkstra - SeqAn API Documentation

# fn() dijkstra
Computes shortest paths from a single source in a graph.

Defined in | <seqan/graph_algorithms.h>
Signature | `void dijkstra(predecessor, distance, g, source, weight);`

## Parameters

`predecessor` | A property map. A property map that represents predecessor relationships among vertices. It determines a shortest-paths tree.
`distance` | A property map.Indicates for each vertex the distance from the source.
`g` | A graph. Types: Directed Graph
`source` | A source vertex. Types: VertexDescriptor
`weight` | A weight map. A property map with edge weights. Edge weights have to be nonnegative.

## Detailed Description

### Remarks

Edge weights have to be nonnegative.

### Example

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

    using namespace seqan2;

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

        // Create graph with 10 directed edges (0,1), (0,3), ...
        TSize numEdges = 10;
        TVertexDescriptor edges[] = {0, 1, 0, 3, 1, 2, 1, 3, 2, 4, 3, 1, 3, 2, 3, 4, 4, 0, 4, 2};
        TGraph g;
        addEdges(g, edges, numEdges);

        // Fill external edge weight map.
        unsigned weights[] = {10, 5, 1, 2, 4, 3, 9, 2, 7, 6};
        String<unsigned> weightMap;
        assignEdgeMap(weightMap, g, weights);

        // Run Dijkstra's algorithm from vertex 0.
        String<unsigned> predMap;
        String<unsigned> distMap;
        dijkstra(predMap, distMap, g, 0, weightMap);

        // Print results to stdout.
        std::cout << "Single-Source Shortest Paths: \n";
        typedef Iterator<TGraph, VertexIterator>::Type TVertexIterator;
        TVertexIterator it(g);
        while (!atEnd(it))
        {
            std::cout << "Path from 0 to " << getValue(it) << ": ";
            _printPath(g, predMap, (TVertexDescriptor) 0, getValue(it));
            std::cout << " (Distance: " << getProperty(distMap, getValue(it)) << ")\n";
            goNext(it);
        }

        // We can achieve the same thing using an internal map that is edge cargos.
        typedef unsigned int TEdgeCargo;
        typedef Directed<TEdgeCargo> TEdges;
        typedef Graph<TEdges> TCargoGraph;

        // Construct graph with the same edges as above.
        TCargoGraph cargoG;
        addEdges(cargoG, edges, numEdges);

        // Fill internal edge weight map.
        InternalPropertyMap<TEdgeCargo> intMap;
        assignEdgeMap(intMap, cargoG, weights);

        // Run Dijkstra's algorithm from vertex 0.
        clear(predMap);
        clear(distMap);
        dijkstra(predMap, distMap, cargoG, 0, intMap);

        // Print result to stdout.
        std::cout << "\nSingle-Source Shortest Paths: \n";
        typedef Iterator<TCargoGraph, VertexIterator>::Type TCargoVertexIterator;
        TCargoVertexIterator itC(cargoG);
        while (!atEnd(itC))
        {
            std::cout << "Path from 0 to " << getValue(itC) << ": ";
            _printPath(g, predMap, (TVertexDescriptor)0, getValue(itC));
            std::cout << " (Distance: " << getProperty(distMap, getValue(itC)) << ")\n";
            goNext(itC);
        }

        return 0;
    }

Demo: demos/dox/graph_algorithms/dijkstra.cpp

    Single-Source Shortest Paths:
    Path from 0 to 0: 0 (Distance: 0)
    Path from 0 to 1: 0,3,1 (Distance: 8)
    Path from 0 to 2: 0,3,1,2 (Distance: 9)
    Path from 0 to 3: 0,3 (Distance: 5)
    Path from 0 to 4: 0,3,4 (Distance: 7)

    Single-Source Shortest Paths:
    Path from 0 to 0: 0 (Distance: 0)
    Path from 0 to 1: 0,3,1 (Distance: 8)
    Path from 0 to 2: 0,3,1,2 (Distance: 9)
    Path from 0 to 3: 0,3 (Distance: 5)
    Path from 0 to 4: 0,3,4 (Distance: 7)

## Data Races

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

## See Also

- bellmanFordAlgorithm
- dagShortestPath

#### Dox Sources

    /*!
     * @fn dijkstra
     *
     * @headerfile <seqan/graph_algorithms.h>
     *
     * @brief Computes shortest paths from a single source in a graph.
     *
     * @signature void dijkstra(predecessor, distance, g, source, weight);
     *
     * @param[out] predecessor A property map. A property map that represents
     *                         predecessor relationships among vertices. It
     *                         determines a shortest-paths tree.
     * @param[out] distance A property map.Indicates for each vertex the distance
     *                      from the source.
     * @param[in] g A graph. Types: Directed Graph
     * @param[in] source A source vertex. Types: VertexDescriptor
     * @param[in] weight A weight map. A property map with edge weights. Edge
     *                   weights have to be nonnegative.
     *
     * @section Remarks
     *
     * Edge weights have to be nonnegative.
     *
     * @section Example
     *
     * @include demos/dox/graph_algorithms/dijkstra.cpp
     *
     * @include demos/dox/graph_algorithms/dijkstra.cpp.stdout
     *
     * @see dagShortestPath
     * @see bellmanFordAlgorithm
     */