// ---------- begin ModInt ---------- mod modint { #[allow(dead_code)] pub struct Mod; impl ConstantModulo for Mod { const MOD: u32 = 1_000_000_007; } #[allow(dead_code)] pub struct RuntimeMod; static mut RUNTIME_MOD: u32 = 0; impl Modulo for RuntimeMod { fn modulo() -> u32 { unsafe { RUNTIME_MOD } } } #[allow(dead_code)] impl RuntimeMod { pub fn set_modulo(p: u32) { unsafe { RUNTIME_MOD = p; } } } use std::marker::*; use std::ops::*; pub trait Modulo { fn modulo() -> u32; } pub trait ConstantModulo { const MOD: u32; } impl Modulo for T where T: ConstantModulo, { fn modulo() -> u32 { T::MOD } } pub struct ModularInteger(pub u32, PhantomData); impl Clone for ModularInteger { fn clone(&self) -> Self { ModularInteger::new_unchecked(self.0) } } impl Copy for ModularInteger {} impl Add for ModularInteger { type Output = ModularInteger; fn add(self, rhs: Self) -> Self::Output { let mut d = self.0 + rhs.0; if d >= T::modulo() { d -= T::modulo(); } ModularInteger::new_unchecked(d) } } impl AddAssign for ModularInteger { fn add_assign(&mut self, rhs: Self) { *self = *self + rhs; } } impl Sub for ModularInteger { type Output = ModularInteger; fn sub(self, rhs: Self) -> Self::Output { let mut d = T::modulo() + self.0 - rhs.0; if d >= T::modulo() { d -= T::modulo(); } ModularInteger::new_unchecked(d) } } impl SubAssign for ModularInteger { fn sub_assign(&mut self, rhs: Self) { *self = *self - rhs; } } impl Mul for ModularInteger { type Output = ModularInteger; fn mul(self, rhs: Self) -> Self::Output { let v = self.0 as u64 * rhs.0 as u64 % T::modulo() as u64; ModularInteger::new_unchecked(v as u32) } } impl MulAssign for ModularInteger { fn mul_assign(&mut self, rhs: Self) { *self = *self * rhs; } } impl Neg for ModularInteger { type Output = ModularInteger; fn neg(self) -> Self::Output { if self.0 == 0 { Self::zero() } else { Self::new_unchecked(T::modulo() - self.0) } } } impl std::fmt::Display for ModularInteger { fn fmt<'a>(&self, f: &mut std::fmt::Formatter<'a>) -> std::fmt::Result { write!(f, "{}", self.0) } } impl std::str::FromStr for ModularInteger { type Err = std::num::ParseIntError; fn from_str(s: &str) -> Result { let val = s.parse::()?; Ok(ModularInteger::new(val)) } } impl From for ModularInteger { fn from(val: usize) -> ModularInteger { ModularInteger::new_unchecked((val % T::modulo() as usize) as u32) } } impl From for ModularInteger { fn from(val: i64) -> ModularInteger { let m = T::modulo() as i64; ModularInteger::new((val % m + m) as u32) } } impl ModularInteger { pub fn new_unchecked(d: u32) -> Self { ModularInteger(d, PhantomData) } pub fn zero() -> Self { ModularInteger::new_unchecked(0) } pub fn one() -> Self { ModularInteger::new_unchecked(1) } } #[allow(dead_code)] impl ModularInteger { pub fn new(d: u32) -> Self { ModularInteger::new_unchecked(d % T::modulo()) } pub fn pow(&self, mut n: u32) -> Self { let mut t = Self::one(); let mut s = *self; while n > 0 { if n & 1 == 1 { t *= s; } s *= s; n >>= 1; } t } pub fn inv(&self) -> Self { assert!(self.0 != 0); self.pow(T::modulo() - 2) } } // ---------- begin Precalc ---------- #[allow(dead_code)] pub struct Precalc { inv: Vec>, fact: Vec>, ifact: Vec>, } #[allow(dead_code)] impl Precalc { pub fn new(n: usize) -> Precalc { let mut inv = vec![ModularInteger::one(); n + 1]; let mut fact = vec![ModularInteger::one(); n + 1]; let mut ifact = vec![ModularInteger::one(); n + 1]; for i in 2..(n + 1) { fact[i] = fact[i - 1] * ModularInteger::new_unchecked(i as u32); } ifact[n] = fact[n].inv(); if n > 0 { inv[n] = ifact[n] * fact[n - 1]; } for i in (1..n).rev() { ifact[i] = ifact[i + 1] * ModularInteger::new_unchecked((i + 1) as u32); inv[i] = ifact[i] * fact[i - 1]; } Precalc { inv: inv, fact: fact, ifact: ifact, } } pub fn inv(&self, n: usize) -> ModularInteger { assert!(n > 0); self.inv[n] } pub fn fact(&self, n: usize) -> ModularInteger { self.fact[n] } pub fn ifact(&self, n: usize) -> ModularInteger { self.ifact[n] } pub fn comb(&self, n: usize, k: usize) -> ModularInteger { if k > n { return ModularInteger::zero(); } self.fact[n] * self.ifact[k] * self.ifact[n - k] } } // ---------- end Precalc ---------- } // ---------- begin Tree DP ---------- struct TreeDP { size: usize, graph: Vec>, init: Init, merge: Merge, phantom: std::marker::PhantomData, } impl TreeDP where Edge: Clone, Value: Clone, Init: Fn(usize) -> Value, Merge: Fn(Value, Value, &Edge) -> Value, { fn new(size: usize, init: Init, merge: Merge) -> Self { TreeDP { size: size, graph: vec![vec![]; size], init: init, merge: merge, phantom: std::marker::PhantomData, } } fn add_edge(&mut self, a: usize, b: usize, c: Edge) { assert!(a < self.size && b < self.size && a != b); self.graph[a].push((b, c.clone())); self.graph[b].push((a, c)); } fn solve(&self, root: usize) -> Value { let size = self.size; let graph = &self.graph; let mut topo = vec![]; let mut parent = vec![root; size]; let mut stack = vec![root]; while let Some(v) = stack.pop() { topo.push(v); for e in graph[v].iter() { if e.0 != parent[v] { parent[e.0] = v; stack.push(e.0); } } } assert!(topo.len() == size); let mut dp: Vec> = (0..size).map(|_| None).collect(); for &v in topo.iter().rev() { let mut now = (self.init)(v); for u in graph[v].iter() { if u.0 == parent[v] { continue; } let b = dp[u.0].take().unwrap(); now = (self.merge)(now, b, &u.1); } dp[v] = Some(now); } dp[root].take().unwrap() } } // ---------- end Tree DP ---------- //https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8 より macro_rules! input { (source = $s:expr, $($r:tt)*) => { let mut iter = $s.split_whitespace(); input_inner!{iter, $($r)*} }; ($($r:tt)*) => { let s = { use std::io::Read; let mut s = String::new(); std::io::stdin().read_to_string(&mut s).unwrap(); s }; let mut iter = s.split_whitespace(); input_inner!{iter, $($r)*} }; } macro_rules! input_inner { ($iter:expr) => {}; ($iter:expr, ) => {}; ($iter:expr, $var:ident : $t:tt $($r:tt)*) => { let $var = read_value!($iter, $t); input_inner!{$iter $($r)*} }; } macro_rules! read_value { ($iter:expr, ( $($t:tt),* )) => { ( $(read_value!($iter, $t)),* ) }; ($iter:expr, [ $t:tt ; $len:expr ]) => { (0..$len).map(|_| read_value!($iter, $t)).collect::>() }; ($iter:expr, chars) => { read_value!($iter, String).chars().collect::>() }; ($iter:expr, bytes) => { read_value!($iter, String).bytes().collect::>() }; ($iter:expr, usize1) => { read_value!($iter, usize) - 1 }; ($iter:expr, $t:ty) => { $iter.next().unwrap().parse::<$t>().expect("Parse error") }; } // use modint::*; type ModInt = ModularInteger; fn run() { input! { n: usize, e: [(usize1, usize1); n - 1], } type T = (ModInt, ModInt, ModInt); type E = (); let init = |_v: usize| -> T { (ModInt::zero(), ModInt::zero(), ModInt::one()) }; let merge = |a: T, b: T, _c: &E| -> T { (a.0 + b.0 + b.1 + b.2, a.1 + b.1 + b.2, a.2 + b.2) }; let mut solver = TreeDP::new(n, init, merge); let mut child = vec![false; n]; for (a, b) in e { child[b] = true; solver.add_edge(a, b, ()); } let root = child.iter().position(|c| !*c).unwrap(); let ans = solver.solve(root).0; println!("{}", ans); } fn main() { run(); }