Fix includes and add some comments

algorithm/tarjan.h

@@ -1,7 +1,6 @@
 #ifndef TARJAN_H_
 #define TARJAN_H_
 
-#include "graph/digraph.h"
 #include "graph/scc.h"
 
 #include <stack>
@@ -16,10 +15,8 @@ class Tarjan {
 public:
   Tarjan(Digraph<T> G) : G(G) {}
 
-  //
-  std::vector<SCC<T>> findSCC();
+  std::vector<SCC<T>> execute();
 
-  //
   void strongConnect(const T& v);
 private:
   // Necessary info about vertices when running Tarjan's algorithm
@@ -68,7 +65,7 @@ void Tarjan<T>::strongConnect(const T& v) {
 }
 
 template<typename T>
-std::vector<SCC<T>> Tarjan<T>::findSCC() {
+std::vector<SCC<T>> Tarjan<T>::execute() {
   for (const auto& v : G.vertices) {
     if (p[v].index == -1) {
       strongConnect(v);