Split graph folder into graph and tree

graph/dag.h

@@ -1,17 +0,0 @@
-#ifndef DAG_H_
-#define DAG_H_
-
-#include "digraph.h"
-
-namespace graph {
-
-// Directed Acyclic Graph
-template<typename T>
-class DAG {
-public:
-  DAG() = default;
-};
-
-} // namespace graph
-
-#endif

graph/directed_acyclic_graph.h

@@ -0,0 +1,16 @@
+#ifndef DIRECTED_ACYCLIC_GRAPH_H_
+#define DIRECTED_ACYCLIC_GRAPH_H_
+
+#include "digraph.h"
+
+namespace graph {
+
+template<typename T>
+class DirectedAcyclicGraph {
+public:
+  DirectedAcyclicGraph() = default;
+};
+
+} // namespace graph
+
+#endif