calculate tree out of the graph

[arneboe]

• There should be a method that returns a tree representation of the graph
• The tree should be created using bfs starting from the root. This way we get the shortest paths.
• possible signatures are:
  • std::unordered_map<FrameId, std::vector<FrameId>> getTree(const FrameId& root) const
  • std::unordered_map<vertex_descriptor, std::vector<vertex_descriptor,>> getTree(const FrameId& root) const
  • The second one is more efficient because it avoids a lot of lookup calls and vertex_descriptor is cheaper to copy than FrameId aka std::string

[arneboe]

Implemented by 3e315bcdfe45a261a8f6b7aff15bee1c6abc00cb