From 8db7a86187c5af677c3dd73f0930605348df3361 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20M=C3=BCller?= <stefan.mueller@aksdb.de>
Date: Sat, 18 Jul 2026 23:38:08 +0200
Subject: [PATCH] Add Petersen graph generator

---
 src/generators.rs | 65 +++++++++++++++++++++++++++++++++++++++++++++++
 src/lib.rs        |  1 +
 2 files changed, 66 insertions(+)
 create mode 100644 src/generators.rs

diff --git a/src/generators.rs b/src/generators.rs
new file mode 100644
index 0000000..d257851
--- /dev/null
+++ b/src/generators.rs
@@ -0,0 +1,65 @@
+use crate::traits::GraphTopology;
+
+pub fn petersen<G>(
+    graph: &mut G,
+) -> (
+    [<G as GraphTopology>::Vertex; 10],
+    [<G as GraphTopology>::Edge; 15],
+)
+where
+    G: GraphTopology,
+{
+    const N: usize = 5;
+    const K: usize = 2;
+
+    let vertices = core::array::from_fn(|_| graph.add_vertex());
+    let edges = core::array::from_fn(|j| {
+        let i = j / 3;
+        match j % 3 {
+            0 => {
+                let outer = if i < N - 1 { i + 1 } else { 0 };
+                graph.add_edge(vertices[i], vertices[outer])
+            }
+            1 => {
+                let inner = if i < N - K { i + N + K } else { i + K };
+                graph.add_edge(vertices[i + N], vertices[inner])
+            }
+            _ => graph.add_edge(vertices[i], vertices[i + N]),
+        }
+    });
+    (vertices, edges)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::models::AppendGraph;
+
+    #[test]
+    fn petersen() {
+        let mut graph = AppendGraph::new();
+        let (vertices, edges) = super::petersen(&mut graph);
+        assert_eq!(graph.vertex_count(), 10, "unexpected number of added vertices");
+        assert_eq!(graph.edge_count(), 15, "unexpected number of added edges");
+        assert!(
+            graph.vertices().all(|v| graph.degree(v) == 3),
+            "all vertices should have degree 3"
+        );
+        assert_handles_in_graph(&graph, &vertices, &edges);
+    }
+
+    fn assert_handles_in_graph<G: GraphTopology>(
+        graph: &G,
+        vertices: &[G::Vertex],
+        edges: &[G::Edge],
+    ) {
+        assert!(
+            vertices.iter().all(|&v| graph.vertices().any(|u| u == v)),
+            "all returned vertices should be in the graph"
+        );
+        assert!(
+            edges.iter().all(|&e| graph.edges().any(|f| f == e)),
+            "all returned edges should be in the graph"
+        );
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index ffb77ee..593f258 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -128,6 +128,7 @@
 //! [`GraphTopologyDeletion`]: crate::traits::GraphTopologyDeletion
 
 pub mod algorithms;
+pub mod generators;
 pub mod maps;
 pub mod models;
 pub mod traits;