A depth-first graph traversal to find connected components of graph.

dfs.c

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+/*======================================================================
+
+  File: dfs.c
+
+  Created: Tue May  6 09:27:26 2008
+
+  Author: Jostein R. Natvig <Jostein.R.Natvig@sintef.no>
+
+  Revision: $Id$
+  ====================================================================*/
+#include <assert.h>
+
+void dfs (int size, int *ia, int *ja, int *ncolors, int *color, int* work)
+{
+   int i, c;
+
+   int *stack  = work;
+   int *bottom = stack;
+
+   *ncolors = 0; /* colors are nonnegative */
+  
+   for (i=0; i<size; ++i) {
+      color [i] = -(ia[i+1]-ia[i]+1);
+   }
+
+   /* Push seeds on stack */
+   for (i=0; i<size; ++i) {
+      if(color[i] >= 0) {
+         continue;
+      }
+
+      *stack++ = i; /* push i */
+     
+      while ( stack != bottom ) {
+         c = *(stack-1); /* peek */
+
+         if (color[c] < 0){
+            *stack++ = ja[ia[c]-color[c]-2];
+            ++color[c];
+   
+         } else {
+            color[c] = *ncolors;
+            --stack; /* pop c */
+         }
+      }
+      ++*ncolors;
+   }
+}
+
+
+
+
+#if TEST
+#include <stdlib.h>
+#include <stdio.h>
+
+
+/* Test code.  Reads a sparse matrix from a file specified on the   */
+/* command line with file format "m n\n i1 j1 v1\n i2 j2 v2\n ...". */
+/* Computes reorder sequence                                        */
+int main (int argc, char *argv [])
+{
+   int      *color, *work;
+   int       j, ncolors;
+   int size = 8;
+   int ia[] = {0, 1, 2, 4, 5, 5, 7, 7, 8};
+   int ja[] = {1, 2, 0, 3, 4, 5, 6, 6};
+
+   color = malloc (size * sizeof *color);
+   work  = malloc (size * sizeof *work);
+   dfs(size, ia, ja, &ncolors, color, work);
+
+
+   fprintf(stderr, "ncolors = %d\n", ncolors);
+   for (j=0; j<size; ++j) {
+      fprintf(stderr, "%d\n", color[j]);   
+   }
+ 
+
+   free (color);
+   free (work);
+   return 0;
+}
+#endif

dfs.h

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+#ifndef DFS_H_INCLUDED
+#define DFS_H_INCLUDED
+void dfs (int size, int *ia, int *ja, int *ncolors, int *color, int* work);
+#endif