Tarjan

//SCC板子
void tarjan(int u){
	dfn[u]=low[u]=++cnt;
	stk[++top]=u;
	ins[u]=1;
	for(int i=hed[u];i;i=nxt[i]){
		int v=ver[i];
		if(!dfn[v]){
			tarjan(v);
			low[u]=min(low[u],low[v]);
		}
		else if(ins[v]){
			low[u]=min(low[u],dfn[v]);
		}
	}
	if(dfn[u]==low[u]){
		int v;
		cntt++;
		do{
			v=stk[top--];
			ins[v]=0;
			scc[cntt].push_back(v);
			blg[v]=cntt;
		}while(u!=v);
	}
}

//点双连通分量板子
void tarjan(int x){
	dfn[x]=low[x]=++cnt;
	ins[x]=1;
	s.push(x);
	if(!siz[x]){
		dcc[++cntt].push_back(x);
		return ;
	}
	int ch=0;
	for(int i=hed[x];i;i=nxt[i]){
		int y=ver[i];
		if(!dfn[y]){
			tarjan(y);
			low[x]=min(low[x],low[y]);
			if(low[y]>=dfn[x]){
				ch++;
				if(rt!=x||ch>1){
					cut[x]=1;
				}
				cntt++;
				int z;
				do{
					z=s.top();
					ins[z]=0;
					s.pop();
					dcc[cntt].push_back(z);
				}while(y!=z);
				dcc[cntt].push_back(x);
			}
		}
		else{
			low[x]=min(low[x],dfn[y]);
		}
	}
}

//边双连通分量板子
void tarjan(int u,int in_edg){
	dfn[u]=low[u]=++cnt;
	for(int i=hed[u];i;i=nxt[i]){
		int v=ver[i];
		if(!dfn[v]){
			tarjan(v,i);
			low[u]=min(low[u],low[v]);
			if(low[v]>dfn[u]){
				brg[i]=brg[i^1]=1;
			}
		}
		else if(i!=(in_edg^1)){
			low[u]=min(low[u],dfn[v]);
		}
	}
}