甚至下载的测试点也是秒过 输入 4 3 1 2 4 2 2 2 输出 4 1 1 1 2 1 3 1 4

#include<bits/stdc++.h>
using namespace std;
const int N=2e6+5,M=5e5+5;
int e[N],ne[N],h[N],idx=2,dfn[M],low[M],cnt,vis[M],num,n,m;
bool bz[N*2];
vector <int>ans[N*2];
int add(int a,int b){
	e[idx] =b;
	ne[idx]=h[a];
	h[a]=idx++;
}

void tarjan(int u,int fa){
	dfn[u]=low[u]=++cnt;
	for(int i=h[u];i;i=ne[i]){
		int v=e[i];
		if(dfn[v]==0){
			tarjan(v,i);
			if(dfn[u]<low[v]) bz[i]=bz[i^1]=1;
			low[u]=min(low[u],low[v]);
		}
		else if(i!=(fa^1)){	
			low[u]=min(low[u],dfn[v]);
		}
		
	}
}

void dfs(int u,int id){
	vis[u]=id,ans[id-1].push_back(u);
	for(int i=h[u];i;i=ne[i]){
		int v=e[i];
		
		if(vis[v] || bz[i])continue;
		dfs(v,id); 
	}
}


int read(){
	int a=1,b=0;
	char ch=getchar();
	while(ch<'0' || ch>'9'){
		if(ch=='-'){
			a=-a;ch=getchar();
		} 		
	}
	while(ch>='0' && ch<='9'){
		b=(b<<1)+(b<<3)+(ch^48);
		ch=getchar();
	}
	return b;
}

int main(){
	n=read(),m=read();
	for(int i=1;i<=m;i++){
		int u,v;
		u=read(),v=read();
		if(u==v) continue;
		add(u,v),add(v,u);
	}
	for(int i=1;i<=n;i++){
		if(!dfn[i]) tarjan(i,0);
	}
//	for(int i=1;i<=n;i++)cout<<dfn[i]<<" "<<low[i]<<endl;
	for(int i=1;i<=n;i++){
		if(vis[i]==0){
			dfs(i,++num);
		}
	}
	printf("%d\n",num);
	for(int i=0;i<num;i++){
		printf("%d",ans[i].size());
		for(int j=0;j<ans[i].size();j++) printf(" %d",ans[i][j]);
		printf("\n");
	}
	return 0;
}