In file included from main.cpp:55:0:
visitor.h:34:7: error: 'map' does not name a type
       map<Vertex, Vertex> parent_;
       ^~~
visitor.h: In member function 'void BfsVisitor<Vertex>::DiscoverVertex(const Vertex&)':
visitor.h:14:11: error: 'parent_' was not declared in this scope
           parent_[vertex] = current_vertex_;
           ^~~~~~~
visitor.h:14:11: note: suggested alternative: 'Parent'
           parent_[vertex] = current_vertex_;
           ^~~~~~~
           Parent
visitor.h: In member function 'size_t BfsVisitor<Vertex>::DistanceTo(const Vertex&) const':
visitor.h:20:41: error: 'parent_' was not declared in this scope
               Vertex parent_of_target = parent_[current_target];
                                         ^~~~~~~
visitor.h:20:41: note: suggested alternative: 'Parent'
               Vertex parent_of_target = parent_[current_target];
                                         ^~~~~~~
                                         Parent
visitor.h: In member function 'Vertex BfsVisitor<Vertex>::Parent(const Vertex&) const':
visitor.h:30:18: error: 'parent_' was not declared in this scope
           return parent_[vertex];
                  ^~~~~~~
visitor.h:30:18: note: suggested alternative: 'Parent'
           return parent_[vertex];
                  ^~~~~~~
                  Parent