Make bfs return a digraph since shortest-path in-out trees are directed graphs

algorithm/bfs.h

@@ -12,16 +12,16 @@ namespace algo {
 template<typename T>
 class BFS {
 public:
-  BFS(Digraph<T> G, T root) : G(G), root(root) {}
+  BFS(Graph<T> G) : G(G) {}
 
   //
-  std::map<T, std::set<T>> run();
+  Digraph<T> run(const T& root);
 
-  //
+  // Initialize the lookup table that is used to
+  // show which vertices have been traversed 
   std::map<T, bool> initExplore();
 private:
-  Digraph<T> G;
-  T root;
+  Graph<T> G;
 }; 
 
 template<typename T>
@@ -34,7 +34,7 @@ std::map<T, bool> BFS<T>::initExplore() {
 }
 
 template<typename T>
-std::map<T, std::set<T>> BFS<T>::run() {
+Digraph<T> BFS<T>::run(const T& root) {
   std::map<T, std::set<T>> tree;
   std::map<T, bool> graphExplore = initExplore();
   std::queue<T> Q;
@@ -54,7 +54,7 @@ std::map<T, std::set<T>> BFS<T>::run() {
     }
   }
 
-  return tree;
+  return Digraph<T>(tree);
 }
 
 } // namespace algo