Add reverse a digraph function and test

graph/digraph.h

@@ -28,7 +28,15 @@ Digraph<T>::Digraph(std::map<T, std::set<T>> digraph) {
 
 template<typename T>
 Digraph<T> Digraph<T>::reverse() {
-  return Digraph<T>();
+  std::map<T, std::set<T>> revMatrix;
+  
+  for (const auto& v : Graph<T>::adjMatrix) {
+    for (const auto& u : v.second) {
+      revMatrix[u].insert(v.first);
+    }
+  }
+
+  return revMatrix;
 }
 
 } // namespace graph

test/graph_test.cc

@@ -10,6 +10,43 @@ using namespace graph;
 
 TEST_SUITE("Graph") {
 
+  TEST_CASE("Reverse") {
+    // 1 --> 2 --> 4 --> 1
+    //       2 --> 3 --> 5 --> 7 --> 3
+    //                   5 --> 9 --> 6 --> 8 --> 9
+    Digraph<std::uint16_t> G;
+    G.insert(1, 2);
+    G.insert(2, 3);
+    G.insert(2, 4);
+    G.insert(3, 5);
+    G.insert(4, 1);
+    G.insert(5, 7);
+    G.insert(5, 9);
+    G.insert(6, 8);
+    G.insert(7, 3);
+    G.insert(8, 9);
+    G.insert(9, 6);
+
+    REQUIRE_EQ(G.vertices.size(), 9);
+
+    auto RG = G.reverse();
+
+    std::map<std::uint16_t, std::set<std::uint16_t>> exp = {
+      {1, {4}},
+      {2, {1}},
+      {3, {2, 7}},
+      {4, {2}},
+      {5, {3}},
+      {6, {9}},
+      {7, {5}},
+      {8, {6}},
+      {9, {5, 8}}
+    };
+    
+    CHECK_EQ(RG.adjMatrix, exp);
+
+  }
+
   TEST_CASE("SCC T1") {
     // 1 --> 2 --> 4 --> 1
     //       2 --> 3 --> 5 --> 7 --> 3