# HG changeset patch
# User Balazs Dezso <deba@google.com>
# Date 1539791531 -7200
# Node ID 6b79d93e812f3d99e00e90bd5c7a5d04f05f6cc1
# Parent  1e5da3fc4fbceced88d54f3429934054ba559c79
Planar drawing algorithm now works for less than 3 nodes (#611)

diff -r 1e5da3fc4fbc -r 6b79d93e812f lemon/planarity.h
--- a/lemon/planarity.h	Tue May 15 14:16:35 2018 +0200
+++ b/lemon/planarity.h	Wed Oct 17 17:52:11 2018 +0200
@@ -2398,6 +2398,15 @@
     void run(const EmbeddingMap& embedding) {
       typedef SmartEdgeSet<Graph> AuxGraph;
 
+      if (countNodes(_graph) < 3) {
+        int y = 0;
+        for (typename Graph::NodeIt n(_graph); n != INVALID; ++n) {
+          _point_map[n].x = 0;
+          _point_map[n].y = y++;
+        }
+        return;
+      }
+
       if (3 * countNodes(_graph) - 6 == countEdges(_graph)) {
         drawing(_graph, embedding, _point_map);
         return;
diff -r 1e5da3fc4fbc -r 6b79d93e812f test/planarity_test.cc
--- a/test/planarity_test.cc	Tue May 15 14:16:35 2018 +0200
+++ b/test/planarity_test.cc	Wed Oct 17 17:52:11 2018 +0200
@@ -30,10 +30,40 @@
 using namespace lemon;
 using namespace lemon::dim2;
 
-const int lgfn = 4;
+const int lgfn = 8;
 const std::string lgf[lgfn] = {
   "@nodes\n"
   "label\n"
+  "@edges\n"
+  "     label\n",
+
+  "@nodes\n"
+  "label\n"
+  "0\n"
+  "@edges\n"
+  "     label\n",
+
+  "@nodes\n"
+  "label\n"
+  "0\n"
+  "1\n"
+  "@edges\n"
+  "     label\n"
+  "0 1  0\n",
+
+  "@nodes\n"
+  "label\n"
+  "0\n"
+  "1\n"
+  "2\n"
+  "@edges\n"
+  "     label\n"
+  "0 1  0\n"
+  "1 2  1\n"
+  "2 0  2\n",
+
+  "@nodes\n"
+  "label\n"
   "0\n"
   "1\n"
   "2\n"
@@ -136,8 +166,11 @@
       ++face_num;
     }
   }
-  check(face_num + countNodes(graph) - countConnectedComponents(graph) ==
-        countEdges(graph) + 1, "Euler test does not passed");
+
+  if (face_num != 0) {
+    check(face_num + countNodes(graph) - countConnectedComponents(graph) ==
+          countEdges(graph) + 1, "Euler test does not passed");
+  }
 }
 
 void checkKuratowski(const Graph& graph, PE& pe) {