- Merged with old version of warshall.c. Some minor improvements.

src/warshall.c

@@ -16,42 +16,76 @@ graph_fill (int *graph, int nodes, int value)
     }
 }
 
-/**
- * return 1 if no cycle
- * return 0 if cycle
- */
-int
-warshall (int *graph, int size)
+//! Show a graph
+void graph_display (int *graph, int nodes)
 {
   int i;
 
-  int index2 (i, j)
+  int index (const int i, const int j)
   {
-    return (i * size + j);
+    return (i * nodes + j);
   }
 
   i = 0;
-  while (i < size)
+  while (i < nodes)
+    {
+      int j;
+      j = 0;
+      while (j<nodes)
+	{
+	  eprintf ("%i ", graph[index(i,j)]);
+	  j++;
+	}
+      eprintf ("\n");
+      i++;
+    }
+}
+
+
+//! Apply warshall's algorithm to determine the closure of a graph
+/**
+ * If j<i and k<j, then k<i.
+ * Could be done more efficiently but that is irrelevant here.
+ *
+ *@param graph A pointer to the integer array of nodes*nodes elements.
+ *@param nodes The number of nodes in the graph.
+ *@Returns 0 if there is a cycle; and the algorithm aborts, 1 if there is no cycle and the result is okay.
+ */
+int
+warshall (int *graph, int nodes)
+{
+  int i;
+
+  int index (const int i, const int j)
+  {
+    return (i * nodes + j);
+  }
+
+  i = 0;
+  while (i < nodes)
     {
       int j;
 
       j = 0;
-      while (j < size)
+      while (j < nodes)
 	{
-	  if (graph[index2 (j, i)] == 1)
+	  if (graph[index (j, i)] == 1)
 	    {
 	      int k;
 
 	      k = 0;
-	      while (k < size)
+	      while (k < nodes)
 		{
-		  if (graph[index2 (k, j)] == 1)
+		  if (graph[index (k, j)] == 1)
 		    {
 		      if (k == i)
 			{
+			  // Oh no! A cycle.
+			  graph [index (k,i)] = 2;
+			  graph_display (graph, nodes);
 			  return 0;
 			}
-		      graph[index2 (k, i)] = 1;
+		      graph[index (k, i)] = 1;
 		    }
 		  k++;
 		}