# HG changeset patch
# User Balazs Dezso <deba@google.com>
# Date 1375995370 -7200
# Node ID 552e3d1242c641658cdb188d4efe452404fb5f22
# Parent  3e711ee55d3184a42ccc00feb76ca15a724b3c88
Fix biNodeConnected() function (#439)

diff -r 3e711ee55d31 -r 552e3d1242c6 lemon/connectivity.h
--- a/lemon/connectivity.h	Wed Aug 07 06:29:34 2013 +0200
+++ b/lemon/connectivity.h	Thu Aug 08 22:56:10 2013 +0200
@@ -744,8 +744,9 @@
   ///
   /// \brief Check whether an undirected graph is bi-node-connected.
   ///
-  /// This function checks whether the given undirected graph is 
-  /// bi-node-connected, i.e. any two edges are on same circle.
+  /// This function checks whether the given undirected graph is
+  /// bi-node-connected, i.e. a connected graph without articulation
+  /// node.
   ///
   /// \return \c true if the graph bi-node-connected.
   /// \note By definition, the empty graph is bi-node-connected.
@@ -753,6 +754,22 @@
   /// \see countBiNodeConnectedComponents(), biNodeConnectedComponents()
   template <typename Graph>
   bool biNodeConnected(const Graph& graph) {
+    bool hasNonIsolated = false, hasIsolated = false;
+    for (typename Graph::NodeIt n(graph); n != INVALID; ++n) {
+      if (typename Graph::OutArcIt(graph, n) == INVALID) {
+        if (hasIsolated || hasNonIsolated) {
+          return false;
+        } else {
+          hasIsolated = true;
+        }
+      } else {
+        if (hasIsolated) {
+          return false;
+        } else {
+          hasNonIsolated = true;
+        }
+      }
+    }
     return countBiNodeConnectedComponents(graph) <= 1;
   }
 
diff -r 3e711ee55d31 -r 552e3d1242c6 test/connectivity_test.cc
--- a/test/connectivity_test.cc	Wed Aug 07 06:29:34 2013 +0200
+++ b/test/connectivity_test.cc	Thu Aug 08 22:56:10 2013 +0200
@@ -99,6 +99,23 @@
   }
 
   {
+    ListGraph g;
+    ListGraph::NodeMap<bool> map(g);
+
+    ListGraph::Node n1 = g.addNode();
+    ListGraph::Node n2 = g.addNode();
+
+    ListGraph::Edge e1 = g.addEdge(n1, n2);
+    ::lemon::ignore_unused_variable_warning(e1);
+    check(biNodeConnected(g), "Graph is bi-node-connected");
+
+    ListGraph::Node n3 = g.addNode();
+    ::lemon::ignore_unused_variable_warning(n3);
+    check(!biNodeConnected(g), "Graph is not bi-node-connected");
+  }
+
+
+  {
     Digraph d;
     Digraph::NodeMap<int> order(d);
     Graph g(d);