#include<bits/stdc++.h> using namespace std; #define fi first #define se second #define pb push_back #define eb emplace_back #define vi vector<int> #define pi pair<int,int> #define sz(v) (int)(v).size() #define all(v) (v).begin(), (v).end() #define compact(v) (v).erase(unique(all(v)), (v).end()) template<class T> using upq = priority_queue<T, vector<T>, greater<T>>; template<class T> int lwrbound(const vector<T>& a, const T& b, const int s = 0){return int(lower_bound(s + all(a), b) - a.begin());} template<class T> int uprbound(const vector<T>& a, const T& b, const int s = 0){return int(upper_bound(s + all(a), b) - a.begin());} #define FOR(i, a, b) for(int i = (a); i <= (b); i++) #define ROF(i, a, b) for(int i = (a); i >= (b); i--) #define sumof(x) accumulate(all(x), 0ll) #define dbg(x) "[" << #x " = " << (x) << "]" #define el "\n" using ll = long long; using ld = long double; template<class T> bool ckmx(T& a, const T b){return (a < b ? a = b, true : false);} template<class T> bool ckmn(T& a, const T b){return (a > b ? a = b, true : false);} const int MOD = 998244353; void add(int& x, int y){ x += y; if(x >= MOD) x -= MOD; } int mul(int x, int y){ return 1ll * x * y % MOD; } int bpow(int a, int b){ int ans = 1; for(; b; b >>= 1, a = mul(a, a)) if(b & 1) ans = mul(ans, a); return ans; } void Main() { int N, M; cin >> N >> M; vi E(N); FOR(i, 1, M){ int u, v; cin >> u >> v; --u, --v; E[u] |= (1 << v), E[v] |= (1 << u); } vector<vector<pi>> dp((1 << N)); dp[0].eb((1 << N) - 1, 1); FOR(mask, 0, (1 << N) - 1) if(sz(dp[mask])){ sort(all(dp[mask])); { vector<pi> cdp; int sum = dp[mask][0].se; FOR(i, 1, sz(dp[mask]) - 1){ if(dp[mask][i].fi == dp[mask][i - 1].fi){ add(sum, dp[mask][i].se); } else cdp.eb(dp[mask][i - 1].fi, sum), sum = dp[mask][i].se; } cdp.eb(dp[mask].back().fi, sum); swap(cdp, dp[mask]); } int full = (1 << N) - 1; for(pi e : dp[mask]){ int B = e.fi, vdp = e.se; for(int tm = B; tm; tm -= (tm & -tm)){ int i = 31 - __builtin_clz((tm & -tm)); int nB = (B & (full ^ ((1 << (i + 1)) - 1))); nB = nB | (E[i] ^ (E[i] & mask)); dp[mask | (1 << i)].eb(nB, vdp); //cout << mask <<" " << (mask | (1 << i)) <<" " << bitset<3>(B) <<" " << bitset<3>(nB) <<" " << vdp << el; } } } int ans = 0; for(pi e : dp[(1 << N) - 1]){ add(ans, e.se); } cout << mul(ans, mul(M, bpow(2, MOD - 2))) << el; } int32_t main() { ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); #define name "InvMOD" if(fopen(name".INP", "r")){ freopen(name".INP", "r", stdin); freopen(name".OUT", "w", stdout); } int t = 1; while(t--) Main(); return 0; }

amusementpark.cpp: In function 'int32_t main()':
amusementpark.cpp:107:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  107 |         freopen(name".INP", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
amusementpark.cpp:108:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  108 |         freopen(name".OUT", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~