Refactor: Replace std::map and std::set with unordered versions

graph/scc.h

@@ -13,7 +13,8 @@ class SCC : public Digraph<T> {
 public:
   SCC() = default;
 
-  SCC(std::map<T, std::set<T>> G, T id) : Digraph<T>(G), id(id) { normalize(); }
+  SCC(std::unordered_map<T, std::unordered_set<T>> G, T id)
+    : Digraph<T>(G), id(id) { normalize(); }
 
   SCC(Digraph<T> G, T id) : id(id) { normalize(); }