Fix bug in connectedComponents()

Author: tdebatty

src/main/java/info/debatty/java/graphs/Graph.java

@@ -200,11 +200,11 @@ public final void prune(final double threshold) {
     public final ArrayList<Graph<T>> connectedComponents() {
 
         ArrayList<Graph<T>> subgraphs = new ArrayList<Graph<T>>();
-        ArrayList<T> nodes_to_process =
-                new ArrayList<T>(map.keySet());
+        LinkedList<T> nodes_to_process =
+                new LinkedList<T>(map.keySet());
 
-        for (int i = 0; i < nodes_to_process.size(); i++) {
-            T n = nodes_to_process.get(i);
+        while (!nodes_to_process.isEmpty()) {
+            T n = nodes_to_process.peek();
             if (n == null) {
                 continue;
             }
@@ -220,7 +220,7 @@ public final ArrayList<Graph<T>> connectedComponents() {
     private void addAndFollow(
             final Graph<T> subgraph,
             final T node,
-            final ArrayList<T> nodes_to_process) {
+            final LinkedList<T> nodes_to_process) {
 
         nodes_to_process.remove(node);
 

src/test/java/info/debatty/java/graphs/GraphTest.java

@@ -25,7 +25,6 @@
 
 import info.debatty.java.graphs.build.Brute;
 import info.debatty.java.graphs.build.GraphBuilder;
-import info.debatty.java.util.BoundedPriorityQueue;
 import java.io.BufferedOutputStream;
 import java.io.File;
 import java.io.FileInputStream;
@@ -76,6 +75,28 @@ public void testConnectedComponents() {
         assertEquals(2, graph.connectedComponents().size());
     }
 
+    /**
+     * Test the connectedComponents method with isolated nodes (that have no
+     * neighbors).
+     */
+    public void testConnectedComponentsIsolated() {
+        System.out.println("Connected components with isolated nodes...");
+        System.out.println("===========================================");
+        int k = 10;
+        Graph<Double> graph = new Graph<Double>(k);
+        graph.put(15.5, new NeighborList(k));
+        graph.put(1.55, new NeighborList(k));
+        graph.put(1.56, new NeighborList(k));
+        graph.put(1.57, new NeighborList(k));
+        graph.put(1.58, new NeighborList(k));
+        graph.put(1.59, new NeighborList(k));
+        graph.put(1.60, new NeighborList(k));
+
+        ArrayList<Graph<Double>> components = graph.connectedComponents();
+        System.out.println(components);
+        assertEquals(graph.size(), components.size());
+    }
+
         /**
      * Test of stronglyConnectedComponents method, of class Graph.
      */