/// <summary>Finds the minimum paths from the <see cref="Vertex"/> with the specified id to all the other <see cref="Vertices"/> of the graph.</summary>
/// <param name="sourceId">The id of the source <see cref="Vertex"/>.</param>
/// <exception cref="ArgumentNullException"></exception>
public void FindMinimumPathsFrom(string sourceId)
{
if (sourceId == null)
{
throw new ArgumentNullException("sourceId");
}
foreach (DijkstraVertex vtx in Vertices)
{
vtx.PathInformation.SetDefaultValues();
if (vtx.Vertex.Id == sourceId)
{
vtx.PathInformation.MinimumCost = 0;
}
}
BuildMinHeap();
while (HeapSize > 0)
{
DijkstraVertex min = ExtractMin();
foreach (NavigableNeighbor nn in min.Vertex.Neighbors)
{
Relax(min, nn.Neighbor, nn.Cost, nn.ConnectingEdge);
}
}
}
private void MinHeapify(int i)
{
int left = 2 * i + 1;
int right = left + 1;
int min;
if (left < HeapSize && Vertices[left] < Vertices[i])
{
min = left;
}
else
{
min = i;
}
if (right < HeapSize && Vertices[right] < Vertices[min])
{
min = right;
}
if (min != i)
{
DijkstraVertex swap = Vertices[i];
Vertices[i] = Vertices[min];
Vertices[min] = swap;
MinHeapify(min);
}
}
private void Relax(DijkstraVertex source, Vertex target, double cost, Edge connectingEdge)
{
DijkstraVertex trg = Array.Find(Vertices, v => v.Vertex.Id == target.Id);
if (trg.PathInformation.MinimumCost > source.PathInformation.MinimumCost + cost)
{
trg.PathInformation.MinimumCost = source.PathInformation.MinimumCost + cost;
trg.PathInformation.Predecessor = source;
trg.PathInformation.ConnectingEdge = connectingEdge;
}
}
private DijkstraVertex ExtractMin()
{
DijkstraVertex min = Vertices[0];
Vertices[0] = Vertices[HeapSize - 1];
Vertices[HeapSize - 1] = min;
HeapSize--;
MinHeapify(0);
return(min);
}
/// <summary>This constructor initializes the new <c>DijkstraAlgorithm</c> from an array containing all the <see cref="Vertex"/>-s of the <see cref="GraphParser"/>.</summary>
/// <param name="vertices">The <see cref="Vertex"/>-s of the <see cref="GraphParser"/>.</param>
/// <exception cref="ArgumentNullException"></exception>
public DijkstraAlgorithm(Vertex[] vertices)
{
if (vertices == null)
{
throw new ArgumentNullException("vertices");
}
Vertices = new DijkstraVertex[vertices.Length];
for (int i = 0; i < Vertices.Length; i++)
{
Vertices[i] = new DijkstraVertex(vertices[i]);
}
HeapSize = Vertices.Length;
}
