QuickGraph - is there algorithm for find all parents (up to root vertex's) of a set of vertex's

Question

In QuickGraph - is there algorithm for find all parents (up to root vertex\'s) of a set of vertex\'s. In other words all vertex\'s which have somewhere under them (on the w

Answer 1

You either need to maintain a reversed graph, or create a wrapper over the graph that reverses every edge. QuickGraph has the ReversedBidirectionalGraph class that is a wrapper intended just for that, but it does not seem to work with the algorithm classes because of generic type incompatibility. I had to create my own wrapper class:

class ReversedBidirectionalGraphWrapper : IVertexListGraph where TEdge : IEdge 
{
  private BidirectionalGraph _originalGraph;
  public IEnumerable OutEdges(TVertex v)
    {
        foreach (var e in _graph.InEdges(v))
        {
            yield return (TEdge)Convert.ChangeType(new Edge(e.Target, e.Source), typeof(TEdge));
        }
    } //...implement the rest of the interface members using the same trick
}

Then run DFS or BFS on this wrapper:

var w = new ReversedBidirectionalGraphWrapper>(graph);    
var result = new List();    
var alg = new DepthFirstSearchAlgorithm>(w);
alg.TreeEdge += e => result.Add(e.Target);    
alg.Compute(node);

Doug's answer is not correct, because DFS will only visit the downstream subgraph. The predecessor observer does not help.