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

include/algorithm/roditty_zwick.h

@@ -5,8 +5,6 @@
 #include "algorithm/tarjan.h"
 #include "graph/breadth_first_tree.h"
 
-using namespace graph;
-
 namespace algo {
 
 template<typename T>
@@ -14,7 +12,7 @@ class RodittyZwick : public DecrementalReachability<T> {
 public:
   RodittyZwick() = default;
 
-  RodittyZwick(Digraph<T> G) { this->G = G; }
+  explicit RodittyZwick(graph::Digraph<T> G) { this->G = G; }
 
   //
   void init() override;