public static void ShortestPaths(Graph graph, int vStart,
IndexedPriorityQueue.IndexedPriorityQueue reachableNodes,
out double[] pi, out int[] pred)
{
// idea:
// greedy approach,
// always extend a shortest path tree by the minimum reachable node
// reachable nodes and shortest paths lengths are efficiently stored in a heap
pi = new double[graph.Nodes()]; // shortest known path lengths
pred = new int[graph.Nodes()]; // predeceesor nodes for these paths
for (int v = 0; v < graph.Nodes(); v++)
{
pi[v] = System.Double.PositiveInfinity;
pred[v] = -1;
}
pi[vStart] = 0.0;
reachableNodes.Insert(vStart, pi[vStart]);
while (!reachableNodes.Empty())
{
int v = reachableNodes.DeleteMin(); // nearest reachable node
List <Edge> edges = graph.Edges(v);
for (int e = 0; e < edges.Count; e++) // test edges from v
{
int w = edges[e].To();
double weight = edges[e].Weight();
if (pi[w] > pi[v] + weight) // new vertex v leads to shorter path
{
pi[w] = pi[v] + weight;
pred[w] = v;
if (reachableNodes.Contains(w))
{
reachableNodes.Change(w, pi[w]);
}
else
{
reachableNodes.Insert(w, pi[w]);
}
}
}
}
}
public static void ShortestPathsArray(Graph graph, int vStart,
out double[] pi, out int[] pred)
{
ShortestPaths(graph, vStart, new PriorityArray(graph.Nodes()), out pi, out pred);
}