判断无向图是否是树

void dfs(ALGraph graph, int v, bool visit[], int &vnum, int &arcnum)
{
    visit[v] = true;
    vnum++;
    for(ArcNode* edge = graph.adjList[v].first; edge != NULL; edge = edge->next)
    {
        if(!visit[edge->adjvex])
        {
            arcnum++;
            dfs(graph, edge->adjvex, visit, vnum, arcnum);
        }
    }
}

/*
    一个无向图G是一颗树的条件：
    G必须是无回路的连通图或者是n-1条边的连通图
*/
bool isTree(ALGraph graph)
{
    bool visit[MAX_NUM];
    memset(visit, 0, sizeof(visit));
    int vnum = 0, arcnum = 0;//访问过顶点的个数，边的条数
    dfs(graph, 1, visit, vnum, arcnum);
    if(vnum == graph.vexnum && arcnum ==  graph.vexnum - 1)
        return true;
    return false;
}