Optimize 2025 day 8 part 1 using sizes from UnionFind

Author: sim642

src/main/scala/eu/sim642/adventofcode2025/Day8.scala

@@ -39,8 +39,9 @@ object Day8 {
     val closestPairs = iterateClosestPairs(junctionBoxes)
     val (ufAfter, _) = Kruskal.iterate(junctionBoxes, closestPairs)(after)
 
-    ufAfter.groups()
+    ufAfter.rootNodes
       .map(_.size)
+      .toSeq
       .sorted(using Ordering.Int.reverse)
       .take(sizes)
       .product

src/main/scala/eu/sim642/adventofcodelib/UnionFind.scala

@@ -38,8 +38,11 @@ class UnionFind[A](val nodes: Map[A, Node[A]]) {
       new UnionFind(nodes + (yRepr -> yNode.copy(size = xNode.size + yNode.size)) + (xRepr -> xNode.copy(parent = yRepr)))
   }
 
-  def groups(): Seq[Seq[A]] =
-    nodes.keys.groupBy(findRepr).values.map(_.toSeq).toSeq
+  def components: Iterable[Iterable[A]] =
+    nodes.keys.groupBy(findRepr).values
+
+  def rootNodes: Iterable[Node[A]] =
+    nodes.view.filter((x, node) => x == node.parent).values
 
   override def toString: String = nodes.toString()
 }