Question

I’m new to OGDF library and need to find the longest path in an acyclic directed graph (I want to use OGDF built in functions).
I know, it is possible to find longest path using shortest path algorithms with negative weights for edges, but also could not find a proper function for it.
Does OGDF has a specific function to do that?
If yes, how can I use it?

Answer 1

In OGDF, you can find the shortest path between node s and other nodes using ShortestPathWithBFM. The lengths (weights) of edges should be passed to the function, using EdgeArray<int>. Here is the class definition from its source code:

namespace ogdf {

class OGDF_EXPORT ShortestPathWithBFM : public ShortestPathModule
{
public:
 ShortestPathWithBFM() { }

 // computes shortest paths
 // Precond.:
 //
 // returns false iff the graph contains a negative cycle
 bool call(
 const Graph          &G,      // directed graph
 const node           s,       // source node
 const EdgeArray<int> &length, // length of an edge
 NodeArray<int>       &d,      // contains shortest path distances after call
 NodeArray<edge>      &pi
 );


};


} // end namespace ogdf

The algorithm would compute the longest path if you pass lengths in negative.
For more information, please refer to: http://www.ogdf.net/doc-ogdf/classogdf_1_1_shortest_path_with_b_f_m.html