Adding transpose function and corresponding tests.

include/graaflib/graph.h

@@ -228,6 +228,11 @@ using directed_graph = graph<VERTEX_T, EDGE_T, graph_type::DIRECTED>;
 template <typename VERTEX_T, typename EDGE_T>
 using undirected_graph = graph<VERTEX_T, EDGE_T, graph_type::UNDIRECTED>;
 
+template <typename VERTEX_T, typename EDGE_T>
+void get_transposed_graph(
+    const directed_graph<VERTEX_T, EDGE_T>& graph,
+    directed_graph<VERTEX_T, EDGE_T>& out_transposed_graph);
+
 }  // namespace graaf
 
 #include "graph.tpp"

include/graaflib/graph.tpp

@@ -213,4 +213,29 @@ void graph<VERTEX_T, EDGE_T, GRAPH_TYPE_V>::remove_edge(
   std::abort();
 }
 
+template <typename VERTEX_T, typename EDGE_T>
+void get_transposed_graph(
+    const directed_graph<VERTEX_T, EDGE_T>& graph,
+    directed_graph<VERTEX_T, EDGE_T>& out_transposed_graph) {
+  for (const auto [edge_vertices, edge] : graph.get_edges()) {
+    const auto [vertex_id_lhs, vertex_id_rhs] = edge_vertices;
+
+    auto vertex_value_lhs = graph.get_vertex(vertex_id_lhs);
+    auto vertex_value_rhs = graph.get_vertex(vertex_id_rhs);
+    auto edge_type = edge;
+
+    if (!out_transposed_graph.has_vertex(vertex_id_lhs)) {
+      auto vertex_id =
+          out_transposed_graph.add_vertex(vertex_value_lhs, vertex_id_lhs);
+    }
+
+    if (!out_transposed_graph.has_vertex(vertex_id_rhs)) {
+      auto vertex_id =
+          out_transposed_graph.add_vertex(vertex_value_rhs, vertex_id_rhs);
+    }
+
+    out_transposed_graph.add_edge(vertex_id_rhs, vertex_id_lhs, edge_type);
+  }
+}
+
 }  // namespace graaf

test/graaflib/graph_test.cpp

@@ -247,4 +247,28 @@ TYPED_TEST(GraphTest, ConstGetter) {
   ASSERT_NO_THROW(test_getters_on_const_graph(graph));
 }
 
+TEST(GraphTest, Transpose) {
+  // GIVEN
+  using graph_t = directed_graph<int, int>;
+  graph_t graph{};
+  const auto vertex_id_1 = graph.add_vertex(1);
+  const auto vertex_id_2 = graph.add_vertex(2);
+  const auto vertex_id_3 = graph.add_vertex(3);
+  graph.add_edge(vertex_id_1, vertex_id_2, 100);
+  graph.add_edge(vertex_id_2, vertex_id_3, 200);
+  graph.add_edge(vertex_id_3, vertex_id_1, 300);
+
+  // WHEN
+  graph_t transposed_graph{};
+  get_transposed_graph(graph, transposed_graph);
+
+  // THEN
+  EXPECT_EQ(get_weight(transposed_graph.get_edge(vertex_id_2, vertex_id_1)),
+            100);
+  EXPECT_EQ(get_weight(transposed_graph.get_edge(vertex_id_3, vertex_id_2)),
+            200);
+  EXPECT_EQ(get_weight(transposed_graph.get_edge(vertex_id_1, vertex_id_3)),
+            300);
+}
+
 }  // namespace graaf