use std::cmp::*; use std::collections::*; // https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8 macro_rules! input { ($($r:tt)*) => { let stdin = std::io::stdin(); let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock())); let mut next = move || -> String{ bytes.by_ref().map(|r|r.unwrap() as char) .skip_while(|c|c.is_whitespace()) .take_while(|c|!c.is_whitespace()) .collect() }; input_inner!{next, $($r)*} }; } macro_rules! input_inner { ($next:expr) => {}; ($next:expr,) => {}; ($next:expr, $var:ident : $t:tt $($r:tt)*) => { let $var = read_value!($next, $t); input_inner!{$next $($r)*} }; } macro_rules! read_value { ($next:expr, ( $($t:tt),* )) => { ($(read_value!($next, $t)),*) }; ($next:expr, [ $t:tt ; $len:expr ]) => { (0..$len).map(|_| read_value!($next, $t)).collect::>() }; ($next:expr, usize1) => (read_value!($next, usize) - 1); ($next:expr, $t:ty) => ($next().parse::<$t>().expect("Parse error")); } /// Verified by https://atcoder.jp/contests/abc198/submissions/21774342 mod mod_int { use std::ops::*; pub trait Mod: Copy { fn m() -> i64; } #[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord)] pub struct ModInt { pub x: i64, phantom: ::std::marker::PhantomData } impl ModInt { // x >= 0 pub fn new(x: i64) -> Self { ModInt::new_internal(x % M::m()) } fn new_internal(x: i64) -> Self { ModInt { x: x, phantom: ::std::marker::PhantomData } } pub fn pow(self, mut e: i64) -> Self { debug_assert!(e >= 0); let mut sum = ModInt::new_internal(1); let mut cur = self; while e > 0 { if e % 2 != 0 { sum *= cur; } cur *= cur; e /= 2; } sum } #[allow(dead_code)] pub fn inv(self) -> Self { self.pow(M::m() - 2) } } impl>> Add for ModInt { type Output = Self; fn add(self, other: T) -> Self { let other = other.into(); let mut sum = self.x + other.x; if sum >= M::m() { sum -= M::m(); } ModInt::new_internal(sum) } } impl>> Sub for ModInt { type Output = Self; fn sub(self, other: T) -> Self { let other = other.into(); let mut sum = self.x - other.x; if sum < 0 { sum += M::m(); } ModInt::new_internal(sum) } } impl>> Mul for ModInt { type Output = Self; fn mul(self, other: T) -> Self { ModInt::new(self.x * other.into().x % M::m()) } } impl>> AddAssign for ModInt { fn add_assign(&mut self, other: T) { *self = *self + other; } } impl>> SubAssign for ModInt { fn sub_assign(&mut self, other: T) { *self = *self - other; } } impl>> MulAssign for ModInt { fn mul_assign(&mut self, other: T) { *self = *self * other; } } impl Neg for ModInt { type Output = Self; fn neg(self) -> Self { ModInt::new(0) - self } } impl ::std::fmt::Display for ModInt { fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result { self.x.fmt(f) } } impl From for ModInt { fn from(x: i64) -> Self { Self::new(x) } } } // mod mod_int macro_rules! define_mod { ($struct_name: ident, $modulo: expr) => { #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)] struct $struct_name {} impl mod_int::Mod for $struct_name { fn m() -> i64 { $modulo } } } } const MOD: i64 = 998_244_353; define_mod!(P, MOD); type MInt = mod_int::ModInt

; // Depends on MInt.rs fn fact_init(w: usize) -> (Vec, Vec) { let mut fac = vec![MInt::new(1); w]; let mut invfac = vec![0.into(); w]; for i in 1..w { fac[i] = fac[i - 1] * i as i64; } invfac[w - 1] = fac[w - 1].inv(); for i in (0..w - 1).rev() { invfac[i] = invfac[i + 1] * (i as i64 + 1); } (fac, invfac) } fn dfs(v: usize, par: usize, hm: &HashMap>, vis: &mut HashSet) -> usize { if vis.contains(&v) { return 0; } vis.insert(v); let mut s = 1; for &w in &hm[&v] { if w == par { continue; } s += dfs(w, v, hm, vis); } s } fn main() { input! { n: usize, m: usize, ab: [(usize1, usize1); m], } let (fac, invfac) = fact_init(n + m + 1); let mut acc = vec![vec![vec![MInt::new(0); n + 2]; m + 1]; 2 * m + 1]; // acc[x][y][z] = \sum_{0 <= i < z} C(n - x, i) * (i + y - 1)! * 2^{y - 1} for x in 0..min(n, 2 * m) + 1 { let mut cur = MInt::new(2).inv(); for y in 0..m + 1 { for i in if y == 0 { 1 } else { 0 }..n + 1 { let tmp = if i <= n - x { fac[n - x] * invfac[n - x - i] * invfac[i] * fac[i + y - 1] } else { 0.into() }; acc[x][y][i + 1] = acc[x][y][i] + tmp * cur; } cur *= 2; } } let mut tot = MInt::new(0); 'outer: for bits in 0usize..1 << m { let odd = bits.count_ones() % 2 == 1; let mut hm = HashMap::new(); for i in 0..m { if (bits & 1 << i) != 0 { let (a, b) = ab[i]; hm.entry(a).or_insert(vec![]).push(b); hm.entry(b).or_insert(vec![]).push(a); } } let mut f = [0; 3]; for (&_, v) in &hm { if v.len() >= 3 { continue 'outer; } f[v.len()] += 1; } let mut vis = HashSet::new(); let mut np = 0; let mut np1 = 0; for (&k, v) in &hm { if v.len() == 1 { let c = dfs(k, n, &hm, &mut vis); if c > 0 { np += 1; if c == 2 { np1 += 1; } } } } let mut nc = 0; for (&k, _) in &hm { if !vis.contains(&k) { nc += 1; dfs(k, n, &hm, &mut vis); } } // The graph is a sum of paths and cycles. if np > 0 && nc > 0 { continue; } if nc > 0 { if nc >= 2 { continue; } if odd { tot -= 1; } else { tot += 1; } continue; } let nr = n - hm.len(); let mut tmp = MInt::new(0); // Find \sum_{0 <= i <= nr, 0 <= j <= np1, 0 <= k <= np - np1} // C(nr, i) (i+j+k-1)! * 2^{j+k-1} [i + 2j + 3k >= 3] // where j = np1, k = np - np1 { let j = np1; let k = np - np1; let imin = max(2 * j + 3 * k, 3) - (2 * j + 3 * k); let tbl = &acc[hm.len()][j + k]; if imin <= nr { tmp += (tbl[nr + 1] - tbl[imin]) * fac[np1] * invfac[j] * invfac[np1 - j] * fac[np - np1] * invfac[k] * invfac[np - np1 - k]; } } if odd { tot -= tmp; } else { tot += tmp; } } println!("{}", tot); }