Minor performance optimization

vertex_cover/src/owned.rs

@@ -1,5 +1,3 @@
-use std::collections::HashSet;
-
 #[derive(Debug)]
 struct Vertex {
     name: u16,
@@ -50,7 +48,12 @@ impl Graph {
 
         for &e in &vertex.edges {
             let i = self.index[e as usize];
-            self.vertices[i as usize].edges.retain(|&o| o != v);
+            let p = self.vertices[i as usize]
+                .edges
+                .iter()
+                .position(|&o| o == v)
+                .unwrap();
+            self.vertices[i as usize].edges.swap_remove(p);
         }
         // dbg!(&self.index);