Articulation point

int dfs_num[mx], dfs_cnt, dfs_low[mx], dfs_parent[mx], n, vis[mx], root, child, art_ver[mx];
vector <int> graph[mx];

void init(){
    dfs_cnt = 1;
    for(int j=1;j<=n;j++){
        if(dfs_num[j]==0){
            root = j; child = 0;
            articulationpoint(j);
            art_ver[j] = (child>1);
        }
    }
    ans = 0;
    for(int j=1;j<=n;j++){
        if(art_ver[j]){
            ans++;
        }
    }
}

void articulationpoint(int u){
    dfs_low[u] = dfs_num[u] = dfs_cnt++;
    for(int i=0;i<graph[u].size();i++){
        if(dfs_num[graph[u][i]] == 0){
            dfs_parent[graph[u][i]] = u;
            if(u==root){
                child++;
                //cout << "root " << graph[u][i] <<" ";
            }
            articulationpoint(graph[u][i]);
            if(dfs_low[graph[u][i]]>=dfs_num[u]){
                art_ver[u] = 1;
            }
            dfs_low[u] = min(dfs_low[u], dfs_low[graph[u][i]]);
        }
        else if(graph[u][i]!=dfs_parent[u]){
            dfs_low[u] = min(dfs_low[u], dfs_num[graph[u][i]]);
        }
    }
}