public java.util.LinkedList <Edge> RemoveNode(String label)
{
java.util.LinkedList <Edge> edges = new java.util.LinkedList <Edge>();
if (nodes.ContainsKey(label))
{
Node node = nodes[label];
nodes.Remove(label);
edges.addAll(node.GetEdges());
edges.addAll(RemoveEdgesToNode(label));
}
return(edges);
}
public java.util.LinkedList <Edge> GetEdgeList()
{
java.util.LinkedList <Edge> edgeList = new java.util.LinkedList <Edge>();
foreach (Node node in nodes.Values)
{
edgeList.addAll(node.GetEdges());
}
return(edgeList);
}
/**
* Computes the K shortest paths in a graph from node s to node t using Yen's algorithm
*
* @param graph the graph on which to compute the K shortest paths from s to t
* @param sourceLabel the starting node for all of the paths
* @param targetLabel the ending node for all of the paths
* @param K the number of shortest paths to compute
* @return a list of the K shortest paths from s to t, ordered from shortest to longest
*/
public IList <Path> Ksp(Graph graph, String sourceLabel, String targetLabel, int K)
{
// Initialize containers for candidate paths and k shortest paths
List <Path> ksp = new List <Path>();
java.util.PriorityQueue <Path> candidates = new java.util.PriorityQueue <Path>();
//try {
/* Compute and add the shortest path */
Path kthPath = Dijkstra.ShortestPath(graph, sourceLabel, targetLabel);
ksp.Add(kthPath);
/* Iteratively compute each of the k shortest paths */
for (int k = 1; k < K; k++)
{
// Get the (k-1)st shortest path
Path previousPath = ksp[k - 1];
/* Iterate over all of the nodes in the (k-1)st shortest path except for the target node; for each node,
* (up to) one new candidate path is generated by temporarily modifying the graph and then running
* Dijkstra's algorithm to find the shortest path between the node and the target in the modified
* graph */
for (int i = 0; i < previousPath.Size(); i++)
{
// Initialize a container to store the modified (removed) edges for this node/iteration
java.util.LinkedList <Edge> removedEdges = new java.util.LinkedList <Edge>();
// Spur node = currently visited node in the (k-1)st shortest path
String spurNode = previousPath.GetEdges().get(i).GetFromNode();
// Root path = prefix portion of the (k-1)st path up to the spur node
Path rootPath = previousPath.CloneTo(i);
/* Iterate over all of the (k-1) shortest paths */
foreach (Path p in ksp)
{
Path stub = p.CloneTo(i);
// Check to see if this path has the same prefix/root as the (k-1)st shortest path
if (rootPath.Equals((object)stub))
{
/* If so, eliminate the next edge in the path from the graph (later on, this forces the spur
* node to connect the root path with an un-found suffix path) */
Edge re = p.GetEdges().get(i);
graph.RemoveEdge(re.GetFromNode(), re.GetToNode());
removedEdges.add(re);
}
}
/* Temporarily remove all of the nodes in the root path, other than the spur node, from the graph */
foreach (Edge rootPathEdge in rootPath.GetEdges())
{
String rn = rootPathEdge.GetFromNode();
if (!rn.Equals(spurNode))
{
removedEdges.addAll(graph.RemoveNode(rn));
}
}
// Spur path = shortest path from spur node to target node in the reduced graph
Path spurPath = Dijkstra.ShortestPath(graph, spurNode, targetLabel);
// If a new spur path was identified...
if (spurPath != null)
{
// Concatenate the root and spur paths to form the new candidate path
Path totalPath = rootPath.Clone();
totalPath.AddPath(spurPath);
// If candidate path has not been generated previously, add it
if (!candidates.contains(totalPath))
{
candidates.add(totalPath, totalPath.GetTotalCost());
}
}
// Restore all of the edges that were removed during this iteration
graph.AddEdges(removedEdges);
}
/* Identify the candidate path with the shortest cost */
bool isNewPath;
do
{
kthPath = candidates.poll();
isNewPath = true;
if (kthPath != null)
{
foreach (Path p in ksp)
{
// Check to see if this candidate path duplicates a previously found path
if (p.Equals(kthPath))
{
isNewPath = false;
break;
}
}
}
} while(!isNewPath);
// If there were not any more candidates, stop
if (kthPath == null)
{
break;
}
// Add the best, non-duplicate candidate identified as the k shortest path
ksp.Add(kthPath);
}
//} catch (Exception e) {
// SystemOut.println(e);
// e.printStackTrace();
//}
// Return the set of k shortest paths
return(ksp);
}