Refactor contract to be a stateless function

src/contractor/contractor.cpp

@@ -73,14 +73,12 @@ int Contractor::Run()
     util::DeallocatingVector<QueryEdge> contracted_edge_list;
     { // own scope to not keep the contractor around
         auto contractor_graph = toContractorGraph(max_edge_id+1, std::move(edge_based_edge_list));
-        GraphContractor graph_contractor(contractor_graph,
+        std::tie(node_levels, is_core_node) = contractGraph(contractor_graph,
                                          std::move(node_levels),
-                                         std::move(node_weights));
-        graph_contractor.Run(config.core_factor);
+                                         std::move(node_weights),
+                                         config.core_factor);
 
         contracted_edge_list = toEdges<QueryEdge>(std::move(contractor_graph));
-        is_core_node = graph_contractor.GetCoreMarker();
-        node_levels = graph_contractor.GetNodeLevels();
     }
     TIMER_STOP(contraction);