Merge pull request 'Update package version' (#10) from release-0.3.1 into main

Reviewed-on: #10

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "grapherity"
-version = "0.3.0"
+version = "0.3.1"
 authors = ["Stefan Müller"]
 edition = "2024"
 rust-version = "1.85.0"

src/generators.rs

@@ -1,6 +1,48 @@
 //! Generators for common graphs.
 
-use crate::traits::{GraphTopology, GraphTopologyAddition};
+use crate::models::AppendGraph;
+use crate::traits::{GraphTopology, GraphTopologyAddition, GraphTopologyConversion};
+
+/// Builds a graph of type `G` by running a generator on a temporary [`AppendGraph`].
+///
+/// `generate_as` fills a temporary graph and converts it to `G`. It returns the handles of the
+/// elements it created as handles of the resulting graph. This makes it possible to obtain graph
+/// types directly that do not implement [`GraphTopologyAddition`], such as [`FrozenGraph`].
+///
+/// # Examples
+///
+/// ```
+/// use grapherity::generators;
+/// use grapherity::models::FrozenGraph;
+/// use grapherity::traits::GraphTopology;
+///
+/// let (graph, vertices, edges) = generators::generate_as::<FrozenGraph, _, _>(generators::petersen);
+/// assert_eq!(graph.vertex_count(), 10);
+/// assert_eq!(graph.edge_count(), 15);
+/// assert!(graph.vertices().all(|v| graph.degree(v) == 3));
+/// ```
+///
+/// [`FrozenGraph`]: crate::models::FrozenGraph
+pub fn generate_as<G, const V: usize, const E: usize>(
+    generator: impl FnOnce(
+        &mut AppendGraph,
+    ) -> (
+        [<AppendGraph as GraphTopology>::Vertex; V],
+        [<AppendGraph as GraphTopology>::Edge; E],
+    ),
+) -> (G, [G::Vertex; V], [G::Edge; E])
+where
+    G: GraphTopologyConversion,
+{
+    let mut builder = AppendGraph::new();
+    let (vertices, edges) = generator(&mut builder);
+    let (graph, iso) = G::convert(&builder);
+    (
+        graph,
+        vertices.map(|v| iso.vertex(v)),
+        edges.map(|e| iso.edge(e)),
+    )
+}
 
 /// Generates a Petersen graph.
 ///
@@ -42,38 +84,128 @@ where
 
 #[cfg(test)]
 mod tests {
+    use std::fmt::Debug;
+
     use super::*;
-    use crate::models::AppendGraph;
+    use crate::models::{FrozenGraph, Graph};
 
     #[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");
+    fn petersen_append_graph() {
+        petersen_add::<AppendGraph>();
+    }
+
+    #[test]
+    fn petersen_graph() {
+        petersen_add::<Graph>();
+    }
+
+    #[test]
+    fn petersen_frozen_graph() {
+        petersen_generate_as::<FrozenGraph>();
+    }
+
+    fn petersen_generate_as<G: GraphTopologyConversion>()
+    where
+        G::Vertex: Debug,
+        G::Edge: Debug,
+    {
+        let (graph, vertices, edges) = generate_as::<G, _, _>(petersen);
+        assert_petersen(&graph, &vertices, &edges);
+    }
+
+    fn petersen_add<G: GraphTopologyAddition>()
+    where
+        G::Vertex: Debug,
+        G::Edge: Debug,
+    {
+        let mut graph = G::default();
+        let (vertices, edges) = petersen(&mut graph);
+        assert_petersen(&graph, &vertices, &edges);
+    }
+
+    fn assert_petersen<G: GraphTopology>(graph: &G, vertices: &[G::Vertex], edges: &[G::Edge])
+    where
+        G::Vertex: Debug,
+        G::Edge: Debug,
+    {
+        assert_element_counts(graph, 10, 15);
+        assert_handles(graph.vertices(), vertices, "vertex");
+        assert_handles(graph.edges(), edges, "edge");
+        assert_no_loops_no_multi_edges(graph);
         assert!(
             graph.vertices().all(|v| graph.degree(v) == 3),
             "all vertices should have degree 3"
         );
-        assert_handles_in_graph(&graph, &vertices, &edges);
+        // Checks that each pair of vertices (u, v) has no common neighbor if they are adjacent, and
+        // exactly one common neighbor otherwise.
+        for (i, &v) in vertices.iter().enumerate() {
+            for &u in &vertices[i + 1..] {
+                if graph.are_adjacent(v, u) {
+                    assert!(
+                        graph.common_neighbors(u, v).next().is_none(),
+                        "adjacent vertices {u:?} and {v:?} should not have a common neighbor"
+                    );
+                } else {
+                    assert_eq!(
+                        graph.common_neighbors(u, v).count(),
+                        1,
+                        "non-adjacent vertices {u:?} and {v:?} should have exactly one common neighbor"
+                    );
+                }
+            }
+        }
     }
 
-    fn assert_handles_in_graph<G: GraphTopology>(
+    fn assert_element_counts<G: GraphTopology>(
         graph: &G,
-        vertices: &[G::Vertex],
-        edges: &[G::Edge],
+        expected_vertex_count: usize,
+        expected_edge_count: usize,
     ) {
-        assert!(
-            vertices.iter().all(|&v| graph.vertices().any(|u| u == v)),
-            "all returned vertices should be in the graph"
+        assert_eq!(
+            graph.vertex_count(),
+            expected_vertex_count,
+            "unexpected number of vertices"
         );
-        assert!(
-            edges.iter().all(|&e| graph.edges().any(|f| f == e)),
-            "all returned edges should be in the graph"
+        assert_eq!(
+            graph.edge_count(),
+            expected_edge_count,
+            "unexpected number of edges"
         );
     }
+
+    /// Asserts that every handle in `returned` is unique and in `all`.
+    fn assert_handles<T: PartialEq + Debug>(
+        all: impl Iterator<Item = T>,
+        returned: &[T],
+        kind: &str,
+    ) {
+        let mut remaining: Vec<T> = all.collect();
+        for e in returned {
+            let Some(position) = remaining.iter().position(|x| x == e) else {
+                panic!("returned {kind} {e:?} is not in the graph or appears more than once");
+            };
+            remaining.swap_remove(position);
+        }
+    }
+
+    fn assert_no_loops_no_multi_edges<G: GraphTopology>(graph: &G)
+    where
+        G::Vertex: Debug,
+        G::Edge: Debug,
+    {
+        for e in graph.edges() {
+            let (u, v) = graph.incident_vertices(e);
+            assert_ne!(u, v, "unexpected loop edge {e:?}");
+        }
+        for v in graph.vertices() {
+            let mut neighbors = Vec::new();
+            for u in graph.adjacent_vertices(v) {
+                assert!(
+                    !neighbors.contains(&u),
+                    "unexpected multi-edge between {v:?} and {u:?}"
+                );
+                neighbors.push(u);
+            }
+        }
+    }
 }

src/maps.rs

@@ -141,9 +141,10 @@ impl<E: Copy, T: Clone> IndexMut<E> for ElementMap<E, T> {
 
 #[cfg(test)]
 mod tests {
-    use super::*;
     use std::rc::Rc;
 
+    use super::*;
+
     #[test]
     fn initial_values_are_default() {
         let map = ElementMap::new(42, |e| e, 6);

src/testing/fixtures.rs

@@ -5,6 +5,7 @@ use crate::models::{AppendGraph, FrozenGraph};
 use crate::traits::{GraphTopology, GraphTopologyAddition, GraphTopologyConversion, Incidence};
 
 pub trait MakeTestGraph: GraphTopology + Sized {
+    /// Returns a versatile, pre-defined standard test graph.
     // Since this is only a test fixture, the complex return type here is deemed acceptable.
     #[allow(clippy::type_complexity)]
     fn standard() -> (
@@ -14,20 +15,32 @@ pub trait MakeTestGraph: GraphTopology + Sized {
         [Vec<Incidence<Self::Vertex, Self::Edge>>; 10],
     );
 
+    /// Returns an empty graph.
     fn empty() -> Self;
 
+    /// Returns a graph with a single vertex and no edges.
     fn single_vertex() -> (Self, Self::Vertex);
 
+    /// Returns a graph with two vertices connected by a single edge.
     fn single_edge() -> (Self, [Self::Vertex; 2], Self::Edge);
 
+    /// Returns a graph with vertices *v0*, *v1*, and *v2*, where *v0* is isolated, and the other
+    /// two are connected by a single edge.
     fn disconnected() -> (Self, [Self::Vertex; 3]);
 
+    /// Returns a graph with a single vertex that has a single loop edge.
     fn loop_edge() -> (Self, Self::Vertex, Self::Edge);
 
+    /// Returns a graph with two vertices that are connected by `K` multi-edges.
     fn multiple_edges<const K: usize>() -> (Self, [Self::Vertex; 2], [Self::Edge; K]);
 
+    /// Returns a graph that is a path with three vertices and two edges between them, returned in
+    /// order.
     fn two_edge_path() -> (Self, [Self::Vertex; 3], [Self::Edge; 2]);
 
+    /// Returns a graph that is a path with three vertices *v0*, *v1*, and *v2*, and two edges
+    /// *e0 = (v0, v1)* and *e1 = (v1, v2)* between them, and two loops on the first two vertices
+    /// *e2 = (v0, v0)* and *e3 = (v1, v1)*.
     fn two_edge_path_with_loops() -> (Self, [Self::Vertex; 3], [Self::Edge; 4]);
 }
 

src/testing/graph_topology_testing.rs

@@ -49,6 +49,12 @@ macro_rules! graph_topology_tests {
             incidence_cursor_copy,
             incident_vertices_incidences_consistency,
             incident_edges_incidences_consistency,
+            common_neighbors,
+            common_neighbors_same_vertex,
+            common_neighbors_single,
+            common_neighbors_disconnected,
+            common_neighbors_multiple_edges,
+            common_neighbors_loop_edge,
         );
     };
 
@@ -771,3 +777,118 @@ where
         );
     }
 }
+
+pub fn common_neighbors<G: MakeTestGraph>()
+where
+    G::Vertex: Debug,
+{
+    let (graph, vertices, _, _) = G::standard();
+    // Pairs of vertex indices with the indices of their expected common neighbors.
+    let cases: [(usize, usize, &[usize]); _] = [
+        (0, 3, &[1]),
+        (1, 6, &[2, 3]),
+        (5, 8, &[]),
+        (2, 9, &[5, 6]),
+        (7, 3, &[]),
+        (0, 1, &[]),
+        (6, 7, &[9]),
+        // Loop only on one side, adjacent.
+        (2, 6, &[2]),
+        // Loop only on one side, not adjacent.
+        (2, 7, &[4]),
+        // Adjacent through a double edge, and both have a loop.
+        (2, 4, &[1, 2, 4]),
+    ];
+    for (i, j, expected) in cases {
+        let expected: Vec<_> = expected.iter().map(|&k| vertices[k]).collect();
+        assert_common_neighbors(&graph, vertices[i], vertices[j], &expected);
+    }
+}
+
+pub fn common_neighbors_same_vertex<G: MakeTestGraph>()
+where
+    G::Vertex: Debug,
+{
+    let (graph, vertices, _, _) = G::standard();
+    // Vertex 1 has a double edge to vertex 0, but no loop.
+    assert_common_neighbors(
+        &graph,
+        vertices[1],
+        vertices[1],
+        &[vertices[0], vertices[2], vertices[3], vertices[4]],
+    );
+    // Vertex 4 has a loop, and is therefore its own common neighbor with itself.
+    assert_common_neighbors(
+        &graph,
+        vertices[4],
+        vertices[4],
+        &[
+            vertices[1],
+            vertices[2],
+            vertices[4],
+            vertices[7],
+            vertices[8],
+        ],
+    );
+}
+
+pub fn common_neighbors_single<G: MakeTestGraph>()
+where
+    G::Vertex: Debug,
+{
+    let (graph, v) = G::single_vertex();
+    assert_common_neighbors(&graph, v, v, &[]);
+}
+
+pub fn common_neighbors_disconnected<G: MakeTestGraph>()
+where
+    G::Vertex: Debug,
+{
+    let (graph, v) = G::disconnected();
+    assert_common_neighbors(&graph, v[0], v[0], &[]);
+    assert_common_neighbors(&graph, v[0], v[1], &[]);
+}
+
+pub fn common_neighbors_multiple_edges<G: MakeTestGraph>()
+where
+    G::Vertex: Debug,
+{
+    let (graph, [v0, v1], _) = G::multiple_edges::<3>();
+    assert_common_neighbors(&graph, v0, v1, &[]);
+    assert_common_neighbors(&graph, v1, v1, &[v0]);
+}
+
+pub fn common_neighbors_loop_edge<G: MakeTestGraph>()
+where
+    G::Vertex: Debug,
+{
+    let (graph, v, _) = G::loop_edge();
+    assert_common_neighbors(&graph, v, v, &[v]);
+}
+
+/// Asserts that `u` and `v` have exactly the `expected` common neighbors, each yielded once, for
+/// both argument orders.
+fn assert_common_neighbors<G: MakeTestGraph>(
+    graph: &G,
+    u: G::Vertex,
+    v: G::Vertex,
+    expected: &[G::Vertex],
+) where
+    G::Vertex: Debug,
+{
+    for (a, b) in [(u, v), (v, u)] {
+        let mut remaining = expected.to_vec();
+        for w in graph.common_neighbors(a, b) {
+            let pos = remaining.iter().position(|&x| x == w).unwrap_or_else(|| {
+                panic!(
+                    "unexpected or repeated common neighbor {w:?} of vertices {a:?} and {b:?} from iterator"
+                )
+            });
+            remaining.swap_remove(pos);
+        }
+        assert!(
+            remaining.is_empty(),
+            "expected common neighbors {remaining:?} of vertices {a:?} and {b:?} were not matched by iterator"
+        );
+    }
+}

src/traits.rs

@@ -175,6 +175,58 @@ pub trait GraphTopology {
     ///
     /// Panics if `v` is not a valid vertex of this graph.
     fn incidence_cursor(&self, v: Self::Vertex) -> Self::IncidenceCursor;
+
+    /// Returns an iterator over all vertices that are adjacent to both `u` and `v`.
+    ///
+    /// Every common neighbor is yielded exactly once, in unspecified order, regardless of how
+    /// many parallel edges connect it to `u` or `v`. This method is symmetric up to permutations,
+    /// i.e. swapping the arguments will yield the same vertices, but not necessarily in the same
+    /// order.
+    ///
+    /// If `u` has a loop and is adjacent to `v`, then `u` is a common neighbor, and will be yielded
+    /// exactly once, and analogously for a loop at `v`.
+    ///
+    /// If `u == v`, then the common neighbors are all neighbors of `u`, including `u` itself if and
+    /// only if it has a loop.
+    ///
+    /// All neighbors of `u` are collected when this method is called, while those of `v` are
+    /// traversed lazily.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `u` or `v` is not a valid vertex of this graph.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use grapherity::models::AppendGraph;
+    /// use grapherity::prelude::*;
+    ///
+    /// let mut graph = AppendGraph::new();
+    /// let [u, w, v] = core::array::from_fn(|_| graph.add_vertex());
+    /// // Parallel edges do not yield `w` more than once.
+    /// graph.add_edge(u, w);
+    /// graph.add_edge(u, w);
+    /// graph.add_edge(w, v);
+    /// assert!(graph.common_neighbors(u, v).eq([w]));
+    /// ```
+    // TODO: FrozenGraph could provide a sorted-merge override, if its vertices were sorted.
+    fn common_neighbors(
+        &self,
+        u: Self::Vertex,
+        v: Self::Vertex,
+    ) -> impl Iterator<Item = Self::Vertex> {
+        // TODO: Instead of Vec, this could use a vertex ElementMap with marked neighbors if the product of the degrees of u and v is large compared to |V|.
+        // TODO: Instead of Vec, this could use a reusable, user-provided(?) "scratch-pad" vertex ElementMap, to not pay its allocation.
+        let mut u_neighbors: Vec<_> = self.adjacent_vertices(u).collect();
+        let mut v_neighbors = self.adjacent_vertices(v);
+        std::iter::from_fn(move || {
+            let w = v_neighbors.find(|w| u_neighbors.contains(w))?;
+            // Removes all parallel entries, so that `w` is not yielded again.
+            u_neighbors.retain(|x| *x != w);
+            Some(w)
+        })
+    }
 }
 
 /// A trait that adds construction operations to an undirected graph topology.