先把一个环缩成一个点处理

然后转化成树形dp解决即可

#include<bits/stdc++.h>
using namespace std;
#define ll long long
const int N=1000010;
const int mod=19260817;
int num[N],low[N];
int ring[N],stk[N];
int belong[N];
int ins[N];
int id,top,scc;
vector<int>e[N];
vector<int>e2[N];
ll f[N];
ll res;
struct node{
	int x,y;
}edge[2*N];
void dfs(int u,int fa){
	
	stk[++top]=u;
	id++;
	num[u]=low[u]=id;
	ins[u]=1;
	for(int i=0;i<(int)e[u].size();i++){
		int v=e[u][i];
		if(v==fa)continue;
		if(num[v]==0){
			dfs(v,u);
			low[u]=min(low[u],low[v]);
		}
		else if(ins[v]){
			low[u]=min(low[u],num[v]);
		}
	}
	if(num[u]==low[u]){
		scc++;
		while(top){
			
			int v=stk[top--];
			ring[scc]++;
			belong[v]=scc;
			ins[v]=0;
			if(v==u)break;
		}
	}
}
void dfs_dp(int u,int fa){
	
	ll tmp=0;
	if(ring[u]>1)f[u]=1;
	for(int i=0;i<(int)e2[u].size();i++){
		
		int v=e2[u][i];
		if(v==fa)continue;
		dfs_dp(v,u);
		tmp+=f[u]*f[v]%mod;
		if(ring[u]>1)f[u]=(f[u]+f[v]*2)%mod;
		else f[u]=(f[u]+f[v])%mod;
	}
	res=(res+tmp)%mod;
}
int main(){
//		freopen("1.txt","r",stdin);
	int n,m;
	cin>>n>>m;
	for(int i=1;i<=m;i++){
		
		
		int x,y;
		cin>>x>>y;
		e[x].push_back(y);
		e[y].push_back(x);
		edge[i]={x,y};
	}
	dfs(1,0);
	for(int i=1;i<=m;i++){
		int u=belong[edge[i].x];
		int v=belong[edge[i].y];
		if(u==v)continue;
		
		e2[u].push_back(v);
		e2[v].push_back(u);
	}
	dfs_dp(1,0);
	cout<<res;
	return 0;
}