+ * into strongly connected components (SCCs).
+ * follows(i, j, user) should return 1 if "i" follows "j" and 0 otherwise.
+ * It should return -1 on error.
+ *
+ * If SCC a contains a node i that follows a node j in another SCC b
+ * (i.e., follows(i, j, user) returns 1), then SCC a will appear after SCC b
+ * in the result.