Add "algorithms" and "models" modules for existing code and related todos

src/models.rs

@@ -0,0 +1,81 @@
+// TODO: Vertex value must not be public.
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub struct Vertex(pub usize);
+
+// TODO: Incidence value must not be public.
+// TODO: Incidence must not be public.
+#[derive(Copy, Clone, PartialEq, Eq)]
+pub struct Incidence(pub usize);
+
+// TODO: VertexIncidenceHeader and its fields must not be public, but without iterators there is currently no other way to access vertex incidences.
+pub struct VertexIncidenceHeader {
+    incidence_count: usize,
+    pub first_incidence: Option<Incidence>,
+}
+
+// TODO: Graph fields must not be public.
+pub struct Graph {
+    // TODO: Index 'incidence_headers' by a 'Vertex' instead of 'Vertex.0'?
+    pub incidence_headers: Vec<VertexIncidenceHeader>,
+    pub next_incidences: Vec<Option<Incidence>>,
+    pub incidence_vertices: Vec<Vertex>,
+}
+
+// TODO: Add iterator of vertices.
+// TODO: Add iterator of edges.
+// TODO: Add iterator of vertex neighbors, see 'fn add_adjacent()'.
+impl Graph {
+    pub fn vertex_count(&self) -> usize {
+        self.incidence_headers.len()
+    }
+
+    pub fn edge_count(&self) -> usize {
+        self.next_incidences.len() / 2
+    }
+
+    pub fn degree(&self, v: Vertex) -> usize {
+        self.incidence_headers[v.0].incidence_count
+    }
+
+    // TODO: 'fn are_adjacent()' could probably be done with a neighbor vertex iterator.
+    pub fn are_adjacent(&self, v1: Vertex, v2: Vertex) -> bool {
+        let Some(mut incidence) = self.incidence_headers[v1.0].first_incidence else {
+            return false;
+        };
+        loop {
+            if self.incidence_vertices[incidence.0] == v2 {
+                return true;
+            }
+            let Some(next) = self.next_incidences[incidence.0] else {
+                return false;
+            };
+            incidence = next;
+        }
+    }
+
+    // TODO: 'fn add_vertex()' should not be publicly accessible for all graph implementations.
+    // TODO: 'fn add_vertex()' needs variants for custom vertex data.
+    pub fn add_vertex(&mut self) -> Vertex {
+        self.incidence_headers.push(VertexIncidenceHeader {
+            incidence_count: 0,
+            first_incidence: None,
+        });
+        Vertex(self.incidence_headers.len() - 1)
+    }
+
+    // TODO: 'fn add_edge()' should not be publicly accessible for all graph implementations.
+    // TODO: 'fn add_edge()' needs variants for custom edge data.
+    pub fn add_edge(&mut self, v1: Vertex, v2: Vertex) {
+        self.add_incidence(v1, v2);
+        self.add_incidence(v2, v1);
+    }
+
+    fn add_incidence(&mut self, v1: Vertex, v2: Vertex) {
+        self.incidence_vertices.push(v2);
+        self.next_incidences
+            .push(self.incidence_headers[v1.0].first_incidence.take());
+        self.incidence_headers[v1.0].incidence_count += 1;
+        self.incidence_headers[v1.0].first_incidence =
+            Some(Incidence(self.incidence_vertices.len() - 1));
+    }
+}