多思考递归的过程！
//DFS实现逆拓扑排序
bool visited[MaxVertexNum];
void DFSTraverse(Graph G){for(v=0;v<G.vexnum;v++)visited[v]=FALSE;for(v=0;v<G.vexnum;v++)if(!visited[v])DFS(G,v);
}
void DFS(Graph G,int v){visit(v);visited[v]=TRUE;for(w=FirstNeighbor(G,v);w>=0;w=NextNeighbor(G,v,w))if(!visited[w]){DFS(G,w);}cout<<v<<endl;
}