总之很NB……

源代码：

#include<bits/stdc++.h>
using namespace std;
int n,m,dfn[20001],cnt,stk[20001],s,sum;
vector<int>a[20001],sc[2001];
int dfs(int u,int f){
	int lowu=dfn[u]=++s,c=0,v,lowv;
	stk[++cnt]=u;
	for(int i=0;i<a[u].size();i++){
		v=a[u][i];
		if(!dfn[v]){
			c++,lowv=dfs(v,u),lowu=min(lowu,lowv);
			if(lowv>=dfn[u]){
				sum++;
				while(stk[cnt+1]!=v)sc[sum].push_back(stk[cnt--]);
				sc[sum].push_back(u);
			}
		}else if(dfn[v]<dfn[u]&&v!=f)lowu=min(lowu,dfn[v]);
	}if(!f&&!c)sc[++sum].push_back(u);
	return lowu;
}
int main(){
	cin>>n>>m;
	for(int i=0;i<m;i++){
		int x,y;
		cin>>x>>y;
		a[x].push_back(y),a[y].push_back(x);
	}for(int i=1;i<=n;i++)if(!dfn[i])cnt=0,dfs(i,0);
	cout<<sum<<endl;
	for(int i=1;i<=sum;i++){
		cout<<a[i].size()<<' ';
		for(int j=0;j<a[i].size();j++)cout<<a[i][j]<<' ';
		cout<<endl;
	}
	return 0;
}