/// <inheritdoc/>
protected override IResult <V, E> InternalSearch(IGraph <V, E> graph, V src, V dst, IEdgeWeigher <V, E> weigher, int maxPaths = -1)
{
// TODO: This method needs to be refactored as it is difficult to follow and debug.
// TODO: There is a defect here triggered by 3+ edges between the same vertices which
// makes an attempt to produce looping paths. Protection against this was added to
// AbstractGraphPathSearch, but the root issue remains here.
// TODO: There is a defect here where not all paths are truly disjoint.
// This class needs to filter its own results to make sure that the paths
// are indeed disjoint. Temporary fix for this is provided, but the issue still
// needs to be addressed through refactoring.
weightF = weigher;
firstDijkstraS = (DefaultResult)base.InternalSearch(graph, src, dst, weigher, AllPaths);
firstDijkstra = (DefaultResult)base.InternalSearch(graph, src, null, weigher, AllPaths);
// Choose an arbitrary shortest path to run Suurballe on.
IPath <V, E> shortPath = null;
if (firstDijkstraS.Paths.Count == 0)
{
return(firstDijkstraS);
}
DisjointPathResult result = new DisjointPathResult(firstDijkstra, src, dst, maxPaths);
foreach (IPath <V, E> p in firstDijkstraS.Paths)
{
shortPath = p;
// Transforms the graph so tree edges have 0 weight.
var modified = new ModifiedWeigher(this);
// Create a residual graph g' by removing all source vertices and reversing 0 length path edges.
IMutableGraph <V, E> gt = MutableCopy(graph);
foreach (E edge in graph.GetEdgesTo(src))
{
gt.RemoveEdge(edge);
}
foreach (E edge in shortPath.Edges)
{
gt.RemoveEdge(edge);
E reverse = (E)Activator.CreateInstance(typeof(E), edge.Dst, edge.Src);
revToEdge.AddOrSet(reverse, edge);
gt.AddEdge(reverse);
}
// Rerun dijkstra on the temporary graph to get a second path.
IResult <V, E> secondDijkstra = new DijkstraGraphSearch <V, E>().Search(gt, src, dst, modified);
IPath <V, E> residualShortPath = null;
if (secondDijkstra.Paths.Count == 0)
{
result.Dpps.Add(new DisjointPathPair <V, E>(shortPath, null));
continue;
}
foreach (IPath <V, E> p2 in secondDijkstra.Paths)
{
residualShortPath = p2;
IMutableGraph <V, E> roundTrip = MutableCopy(graph);
List <E> tmp = roundTrip.Edges.ToList();
tmp.ForEach(roundTrip.RemoveEdge);
foreach (E edge in shortPath.Edges)
{
roundTrip.AddEdge(edge);
}
if (residualShortPath != null)
{
foreach (E edge in residualShortPath.Edges)
{
if (revToEdge.ContainsKey(edge))
{
E edgeToRemove = revToEdge[edge];
if (roundTrip.Edges.Contains(edgeToRemove))
{
roundTrip.RemoveEdge(edgeToRemove);
}
}
else
{
roundTrip.AddEdge(edge);
}
}
}
// Actually build the final result.
DefaultResult lastSearch = (DefaultResult)base.InternalSearch(roundTrip, src, dst, weigher, AllPaths);
IPath <V, E> primary = lastSearch.Paths.First();
foreach (E edge in primary.Edges)
{
roundTrip.RemoveEdge(edge);
}
ISet <IPath <V, E> > backups = base.InternalSearch(roundTrip, src, dst, weigher, AllPaths).Paths;
// Find first backup path that does not share any nodes with the primary.
foreach (IPath <V, E> backup in backups)
{
if (IsDisjoint(primary, backup))
{
result.Dpps.Add(new DisjointPathPair <V, E>(primary, backup));
break;
}
}
}
}
for (int i = result.Dpps.Count - 1; i > 0; --i)
{
if (result.Dpps[i].Size <= 1)
{
result.Dpps.RemoveAt(i);
}
}
result.BuildPaths();
return(result);
}
void IMutableGraph <TVertex, TEdge> .Clear()
{
IMutableGraph <TVertex, TEdge> ithis = this;
}