public static void Dfs(ref Graph g, int in_v, ref string res, ref bool[,] bm)
        {
            if (g.val[in_v].edges.Count != 0)
            {
                res = res + in_v.ToString() + "(";

                for (int i = 0; i < g.val[in_v].edges.Count; i++)
                {
                    bm[g.val[in_v].edges[i], in_v] = true;

                    if (res.Length > 0 && res[res.Length - 1] != '(')
                        res = res + ",";

                    Dfs(ref g, g.val[in_v].edges[i], ref res, ref bm);

                }
                res = res + ")";
            }
            else
                res = res + in_v.ToString();
        }