Add contains method for single vertex and hash function for SCCs

include/graph/graph.h

@@ -27,7 +27,7 @@ public:
   virtual void remove(const T& u, const T& v) =0;
 
   // Return graph vertices
-  auto vertices();
+  auto vertices() const;
 
   // Return num. of vertices
   std::uint16_t V();
@@ -38,11 +38,10 @@ public:
   // Adjacency matrix representation
   std::unordered_map<T, std::unordered_set<T>> adjList;
 
-  friend std::ostream& operator<<<>(std::ostream& os, Graph<T>& G);
 };
 
 template<typename T>
-auto Graph<T>::vertices() {
+auto Graph<T>::vertices() const{
   return std::views::keys(adjList);
 }
 
@@ -60,20 +59,7 @@ std::uint16_t Graph<T>::E() {
   return edges;
 }
 
-template<typename T>
-std::ostream& operator<<(std::ostream& os, Graph<T>& G) {
-  os << "V: " << G.V() << " E: " << G.E() << '\n';
-  for (const auto& u : this->vertices()) {
-    if (!this->adjList[u].empty()) {
-      for (const auto& v : this->adjList[u]) {
-        os << u << "->" << v << ' ';
-      }
-      os << '\n';
-    }
-  }
-  os << '\n';
-  return os;
-}
+
 
 } // namespace graph