Graph newGraph(int nV)
{
   assert(nV >= 0);
   int i, j;
   int **e = malloc(nV * sizeof(int *));
   assert(e != NULL);
   for (i = 0; i < nV; i++) {
      e[i] = malloc(nV * sizeof(int));
      assert(e[i] != NULL);
      for (j = 0; j < nV; j++)
         e[i][j] = 0;
   }
   Graph g = malloc(sizeof(GraphRep));
   assert(g != NULL);
   g->nV = nV;  g->nE = 0;  g->edges = e;
   return g;
}