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;
}