이 제출은 이전 버전의 oj.uz에서 채점하였습니다. 현재는 제출 당시와는 다른 서버에서 채점을 하기 때문에, 다시 제출하면 결과가 달라질 수도 있습니다.
#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(long long i=0;i<(long long)(n);i++)
#define REP(i,k,n) for(long long i=k;i<(long long)(n);i++)
#define pb emplace_back
#define lb(v,k) (lower_bound(all(v),(k))-v.begin())
#define ub(v,k) (upper_bound(all(v),(k))-v.begin())
#define fi first
#define se second
#define pi M_PI
#define PQ(T) priority_queue<T>
#define SPQ(T) priority_queue<T,vector<T>,greater<T>>
#define dame(a) {out(a);return 0;}
#define decimal cout<<fixed<<setprecision(15);
#define all(a) a.begin(),a.end()
#define rsort(a) {sort(all(a));reverse(all(a));}
#define dupli(a) {sort(all(a));a.erase(unique(all(a)),a.end());}
#define popcnt __builtin_popcountll
typedef long long ll;
typedef pair<ll,ll> P;
typedef tuple<ll,ll,ll> PP;
typedef tuple<ll,ll,ll,ll> PPP;
using vi=vector<ll>;
using vvi=vector<vi>;
using vvvi=vector<vvi>;
using vvvvi=vector<vvvi>;
using vp=vector<P>;
using vvp=vector<vp>;
using vb=vector<bool>;
using vvb=vector<vb>;
const ll inf=1001001001001001001;
const ll INF=1001001001;
const ll mod=1000000007;
const double eps=1e-10;
template<class T> bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;}
template<class T> bool chmax(T&a,T b){if(a<b){a=b;return true;}return false;}
template<class T> void out(T a){cout<<a<<'\n';}
template<class T> void outp(T a){cout<<'('<<a.fi<<','<<a.se<<')'<<'\n';}
template<class T> void outvp(T v){rep(i,v.size())cout<<'('<<v[i].fi<<','<<v[i].se<<')';cout<<'\n';}
template<class T> void outvvp(T v){rep(i,v.size())outvp(v[i]);}
template<class T> void outv(T v){rep(i,v.size()){if(i)cout<<' ';cout<<v[i];}cout<<'\n';}
template<class T> void outvv(T v){rep(i,v.size())outv(v[i]);}
template<class T> bool isin(T x,T l,T r){return (l)<=(x)&&(x)<=(r);}
template<class T> void yesno(T b){if(b)out("yes");else out("no");}
template<class T> void YesNo(T b){if(b)out("Yes");else out("No");}
template<class T> void YESNO(T b){if(b)out("YES");else out("NO");}
template<class T> void outset(T s){auto itr=s.begin();while(itr!=s.end()){if(itr!=s.begin())cout<<' ';cout<<*itr;itr++;}cout<<'\n';}
void outs(ll a,ll b){if(a>=inf-100)out(b);else out(a);}
ll gcd(ll a,ll b){if(b==0)return a;return gcd(b,a%b);}
ll modpow(ll a,ll b){ll res=1;a%=mod;while(b){if(b&1)res=res*a%mod;a=a*a%mod;b>>=1;}return res;}
ll solve(ll n,ll m,vp edge){
vvi g(n,vi(n));
rep(i,m)g[edge[i].fi][edge[i].se]=1;
vi ord(n);rep(i,n)ord[i]=i;
ll ans=0;
do{
bool ok=true;
rep(i,n-1)if(ord[i]>ord[i+1]&&!g[ord[i]][ord[i+1]]&&!g[ord[i+1]][ord[i]])ok=false;
if(ok){
rep(i,n)REP(j,i+1,n)if(g[ord[j]][ord[i]])ans++;
}
}while(next_permutation(all(ord)));
return ans;
}
ll solve2(ll n,ll m,vp edge){
ll ans=0;
rep(bit,1<<m){
vvi g(n);
rep(i,m){
if(bit>>i&1)g[edge[i].fi].pb(edge[i].se);
else g[edge[i].se].pb(edge[i].fi);
}
queue<ll> que;
vi cnt(n);
rep(i,n)for(ll x:g[i])cnt[x]++;
rep(i,n)if(cnt[i]==0)que.push(i);
while(!que.empty()){
ll i=que.front();que.pop();
for(ll x:g[i]){
cnt[x]--;
if(cnt[x]==0)que.push(x);
}
}
bool ok=true;
rep(i,n)if(cnt[i])ok=false;
if(ok)ans++;
}
return ans*m/2;
}
int main(){
ll n,m;cin>>n>>m;
vp edge(m);
rep(i,m){
ll a,b;cin>>a>>b;a--;b--;
edge[i]=P(a,b);
}
out(solve2(n,m,edge));
}
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