Remove "using namespace" from headers and make single param constructors explicit

include/graph/graph.h

@@ -15,7 +15,7 @@ template<typename T> std::ostream& operator<<(std::ostream& os, Graph<T>& G);
 template<typename T>
 class Graph {
 public:
-  ~Graph();
+  virtual ~Graph() = default;
   
   // Return true if there is a path from u to v
   virtual bool contains(const T& u, const T& v) =0;
@@ -41,11 +41,6 @@ public:
   friend std::ostream& operator<<<>(std::ostream& os, Graph<T>& G);
 };
 
-template<typename T>
-Graph<T>::~Graph() {
-  adjList.clear();
-}
-
 template<typename T>
 auto Graph<T>::vertices() {
   return std::views::keys(adjList);
@@ -62,7 +57,7 @@ std::uint16_t Graph<T>::E() {
   for (const auto& u : vertices()) {
     edges += static_cast<std::uint16_t>(adjList[u].size());
   }
-  return static_cast<std::uint16_t>(edges);
+  return edges;
 }
 
 template<typename T>