Fix is_semi_connected (#1561)

Co-authored-by: Ivan Carvalho <8753214+IvanIsCoding@users.noreply.github.com>

Author: jberg5

src/connectivity/mod.rs

@@ -618,10 +618,10 @@ pub fn is_semi_connected(graph: &digraph::PyDiGraph) -> PyResult<bool> {
     }
 
     let mut temp_graph = DiGraph::new();
-    let mut node_map = Vec::new();
+    let mut node_map = vec![NodeIndex::end(); graph.graph.node_bound()];
 
-    for _node in graph.graph.node_indices() {
-        node_map.push(temp_graph.add_node(()));
+    for node in graph.graph.node_indices() {
+        node_map[node.index()] = temp_graph.add_node(());
     }
 
     for edge in graph.graph.edge_indices() {

tests/digraph/test_is_semi_connected.py

@@ -74,3 +74,14 @@ def test_is_semi_connected_directed_star_graph(self):
     def test_is_semi_connected_directed_grid_graph(self):
         graph = rustworkx.generators.directed_grid_graph(10, 10)
         self.assertEqual(rustworkx.is_semi_connected(graph), naive_semi_connected(graph))
+
+    def test_is_semi_connected_with_node_gaps(self):
+        graph = rustworkx.PyDiGraph()
+        graph.add_nodes_from(list(range(5)))
+        graph.remove_node(1)
+        # Remaining nodes 0, 2, 3, 4 form a path
+        graph.add_edge(0, 2, None)
+        graph.add_edge(2, 3, None)
+        graph.add_edge(3, 4, None)
+
+        self.assertEqual(rustworkx.is_semi_connected(graph), naive_semi_connected(graph))