README.md

Full documentation: http://docs.timwi.de/RT.Dijkstra

This class allows you to find the shortest path through any kind of graph in which the edges have weights.

Usage example

Suppose you have a network of roads that connect cities:

 From         To            Distance
═════════════════════════════════════
 New York     Chicago            789
 New York     Philadelphia        97
 Los Angeles  Phoenix            372
 Chicago      Houston           1083
 Chicago      Philadelphia       759
 Houston      Phoenix           1176

Suppose also that this information is stored in a dictionary such as the following:

public static class CityInfo
{
    public static Dictionary<string, Dictionary<string, int>> Distances;

    static CityInfo()
    {
        // Populate Distances here
    }
}

Now Dijkstra’s Algorithm lets you find the shortest route to get from any city to any other. First, declare a type similar to the following:

public sealed class CityNode : Node<int, string>
{
    public string City { get; private set; }
    public string Destination { get; private set; }

    public CityNode(string city, string destination)
    {
        City = city;
        Destination = destination;
    }

    // This function must return true if the two nodes represent the same city.
    public override bool Equals(Node<int, string> other)
    {
        return City.Equals(((CityNode) other).City);
    }

    public override int GetHashCode() { return City.GetHashCode(); }

    // This function determines whether we’ve arrived at our intended destination.
    public override bool IsFinal { get { return City == Destination; } }

    // This function returns the direct connections from the current city.
    public override IEnumerable<Edge<int, string>> Edges
    {
        get
        {
            return CityInfo.Distances[City].Select(toCity => new Edge<int, string>(
                // The weight of this edge is the distance between the cities.
                toCity.Value,
                // The label of this edge is the travel route.
                string.Format("{0} to {1}", City, toCity.Key),
                // The other city the edge leads to.
                new CityNode(toCity.Key, Destination)));
        }
    }
}

And then a single call to DijkstrasAlgorithm.Run does the actual work. Let’s create a function that returns a human-readable route:

static string GetRoute(string from, string to)
{
    int totalDistance;
    var route = DijkstrasAlgorithm.Run(
		// The start node to begin our search.
		new CityNode(from, to),
		// The initial value for the distance traveled.
		0,
		// How to add two distances.
		(a, b) => a + b,
		// The variable to receive the total distance traveled.
		out totalDistance);

    return string.Format("{0} ({1} miles)", string.Join(", ", route), totalDistance);
}

// This example outputs:
// New York to Chicago, Chicago to Houston, Houston to Phoenix (3048 miles)
Console.WriteLine(GetRoute("New York", "Phoenix"));

// This example outputs:
// Los Angeles to Phoenix, Phoenix to Houston, Houston to Chicago (2631 miles)
Console.WriteLine(GetRoute("Los Angeles", "Chicago"));

// This example outputs:
// Phoenix to Houston (1176 miles)
Console.WriteLine(GetRoute("Phoenix", "Houston"));

// This example outputs an empty route, because we’re already at the destination:
//  (0 miles)
Console.WriteLine(GetRoute("Phoenix", "Phoenix"));