1 void dfs(int u,int father) 2 { 3     int child=0; 4     dfn[u]=low[u]=++dfs_clock; 5      6     for (int c=head[u];c;c=nxt[c]) 7     { 8         int v=to[c]; 9         if (!dfn[v])10         {11             child++;12             dfs(v,u);13             low[u]=min(low[u],low[v]);14             if (low[v]>=dfn[u])15                 is_cut[u]=true;16         }17         else if (v!=father)18             low[u]=min(low[u],dfn[v]);19     }20     21     if (!father && child==1)22         is_cut[u]=0;23 }