test/loj/3350.test.cpp

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Last update: 2025-08-12 18:01:36+09:00
Problem: https://loj.ac/p/3350

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Code

// competitive-verifier: PROBLEM https://loj.ac/p/3350
// competitive-verifier: TLE 0.5
// competitive-verifier: MLE 64

#include <iostream>
#include "src/Math/ModInt.hpp"
#include "src/LinearAlgebra/Matrix.hpp"
#include "src/Graph/Graph.hpp"
#include "src/Graph/Rerooting.hpp"
using namespace std;
signed main() {
 cin.tie(0);
 ios::sync_with_stdio(0);
 using Mint= ModInt<int(1e9 + 7)>;
 using Mat= Matrix<Mint>;
 long long N, D;
 cin >> N >> D;
 Graph g(N, N - 1);
 for (auto &e: g) cin >> e, --e;
 auto put_edge= [](int, int, Mat x) {
  swap(x[0][0], x[1][0]);
  swap(x[0][1], x[1][1]);
  return x;
 };
 auto op= [](const Mat &l, const Mat &r) {
  Mat ret(2, 2);
  for (int i= 2; i--;)
   for (int j= 2; j--;) {
    ret[i & j][1]+= l[i][1] * r[j][0] + l[i][0] * r[j][1];
    ret[i & j][0]+= l[i][0] * r[j][0];
   }
  return ret;
 };
 Mat ui(2, 2);
 ui[1][0]= 1;
 auto put_vertex= [](int, Mat x) {
  x[0][1]+= 1;
  return x;
 };
 Rerooting<Mat> dp(g, put_edge, op, ui, put_vertex);
 Mat sum(2, 2);
 for (int i= N; i--;) sum+= dp[i];
 auto M= sum;
 M[0][0]*= N, M[1][0]*= N;
 auto A= dp[0];
 A[0][0]*= N, A[1][0]*= N;
 Mint ans= (A * M.pow(D - 1) * sum)[0][0];
 cout << ans << '\n';
 return 0;
}

#line 1 "test/loj/3350.test.cpp"
// competitive-verifier: PROBLEM https://loj.ac/p/3350
// competitive-verifier: TLE 0.5
// competitive-verifier: MLE 64

#include <iostream>
#line 2 "src/Math/mod_inv.hpp"
#include <utility>
#include <type_traits>
#include <cassert>
template <class Uint> constexpr inline Uint mod_inv(Uint a, Uint mod) {
 std::make_signed_t<Uint> x= 1, y= 0, z= 0;
 for (Uint q= 0, b= mod, c= 0; b;) z= x, x= y, y= z - y * (q= a / b), c= a, a= b, b= c - b * q;
 return assert(a == 1), x < 0 ? mod - (-x) % mod : x % mod;
}
#line 2 "src/Internal/Remainder.hpp"
namespace math_internal {
using namespace std;
using u8= unsigned char;
using u32= unsigned;
using i64= long long;
using u64= unsigned long long;
using u128= __uint128_t;
struct MP_Na {  // mod < 2^32
 u32 mod;
 constexpr MP_Na(): mod(0) {}
 constexpr MP_Na(u32 m): mod(m) {}
 constexpr inline u32 mul(u32 l, u32 r) const { return u64(l) * r % mod; }
 constexpr inline u32 set(u32 n) const { return n; }
 constexpr inline u32 get(u32 n) const { return n; }
 constexpr inline u32 norm(u32 n) const { return n; }
 constexpr inline u32 plus(u64 l, u32 r) const { return l+= r, l < mod ? l : l - mod; }
 constexpr inline u32 diff(u64 l, u32 r) const { return l-= r, l >> 63 ? l + mod : l; }
};
template <class u_t, class du_t, u8 B> struct MP_Mo {  // mod < 2^32, mod < 2^62
 u_t mod;
 constexpr MP_Mo(): mod(0), iv(0), r2(0) {}
 constexpr MP_Mo(u_t m): mod(m), iv(inv(m)), r2(-du_t(mod) % mod) {}
 constexpr inline u_t mul(u_t l, u_t r) const { return reduce(du_t(l) * r); }
 constexpr inline u_t set(u_t n) const { return mul(n, r2); }
 constexpr inline u_t get(u_t n) const { return n= reduce(n), n >= mod ? n - mod : n; }
 constexpr inline u_t norm(u_t n) const { return n >= mod ? n - mod : n; }
 constexpr inline u_t plus(u_t l, u_t r) const { return l+= r, l < (mod << 1) ? l : l - (mod << 1); }
 constexpr inline u_t diff(u_t l, u_t r) const { return l-= r, l >> (B - 1) ? l + (mod << 1) : l; }
private:
 u_t iv, r2;
 static constexpr u_t inv(u_t n, int e= 6, u_t x= 1) { return e ? inv(n, e - 1, x * (2 - x * n)) : x; }
 constexpr inline u_t reduce(const du_t &w) const { return u_t(w >> B) + mod - ((du_t(u_t(w) * iv) * mod) >> B); }
};
using MP_Mo32= MP_Mo<u32, u64, 32>;
using MP_Mo64= MP_Mo<u64, u128, 64>;
struct MP_Br {  // 2^20 < mod <= 2^41
 u64 mod;
 constexpr MP_Br(): mod(0), x(0) {}
 constexpr MP_Br(u64 m): mod(m), x((u128(1) << 84) / m) {}
 constexpr inline u64 mul(u64 l, u64 r) const { return rem(u128(l) * r); }
 static constexpr inline u64 set(u64 n) { return n; }
 constexpr inline u64 get(u64 n) const { return n >= mod ? n - mod : n; }
 constexpr inline u64 norm(u64 n) const { return n >= mod ? n - mod : n; }
 constexpr inline u64 plus(u64 l, u64 r) const { return l+= r, l < (mod << 1) ? l : l - (mod << 1); }
 constexpr inline u64 diff(u64 l, u64 r) const { return l-= r, l >> 63 ? l + (mod << 1) : l; }
private:
 u64 x;
 constexpr inline u128 quo(const u128 &n) const { return (n * x) >> 84; }
 constexpr inline u64 rem(const u128 &n) const { return n - quo(n) * mod; }
};
template <class du_t, u8 B> struct MP_D2B1 {  // mod < 2^63, mod < 2^64
 u64 mod;
 constexpr MP_D2B1(): mod(0), s(0), d(0), v(0) {}
 constexpr MP_D2B1(u64 m): mod(m), s(__builtin_clzll(m)), d(m << s), v(u128(-1) / d) {}
 constexpr inline u64 mul(u64 l, u64 r) const { return rem((u128(l) * r) << s) >> s; }
 constexpr inline u64 set(u64 n) const { return n; }
 constexpr inline u64 get(u64 n) const { return n; }
 constexpr inline u64 norm(u64 n) const { return n; }
 constexpr inline u64 plus(du_t l, u64 r) const { return l+= r, l < mod ? l : l - mod; }
 constexpr inline u64 diff(du_t l, u64 r) const { return l-= r, l >> B ? l + mod : l; }
private:
 u8 s;
 u64 d, v;
 constexpr inline u64 rem(const u128 &u) const {
  u128 q= (u >> 64) * v + u;
  u64 r= u64(u) - (q >> 64) * d - d;
  if (r > u64(q)) r+= d;
  if (r >= d) r-= d;
  return r;
 }
};
using MP_D2B1_1= MP_D2B1<u64, 63>;
using MP_D2B1_2= MP_D2B1<u128, 127>;
template <class u_t, class MP> constexpr u_t pow(u_t x, u64 k, const MP &md) {
 for (u_t ret= md.set(1);; x= md.mul(x, x))
  if (k & 1 ? ret= md.mul(ret, x) : 0; !(k>>= 1)) return ret;
}
}
#line 3 "src/Internal/modint_traits.hpp"
namespace math_internal {
struct m_b {};
struct s_b: m_b {};
}
template <class mod_t> constexpr bool is_modint_v= std::is_base_of_v<math_internal::m_b, mod_t>;
template <class mod_t> constexpr bool is_staticmodint_v= std::is_base_of_v<math_internal::s_b, mod_t>;
#line 6 "src/Math/ModInt.hpp"
namespace math_internal {
template <class MP, u64 MOD> struct SB: s_b {
protected:
 static constexpr MP md= MP(MOD);
};
template <class U, class B> struct MInt: public B {
 using Uint= U;
 static constexpr inline auto mod() { return B::md.mod; }
 constexpr MInt(): x(0) {}
 template <class T, typename= enable_if_t<is_modint_v<T> && !is_same_v<T, MInt>>> constexpr MInt(T v): x(B::md.set(v.val() % B::md.mod)) {}
 constexpr MInt(__int128_t n): x(B::md.set((n < 0 ? ((n= (-n) % B::md.mod) ? B::md.mod - n : n) : n % B::md.mod))) {}
 constexpr MInt operator-() const { return MInt() - *this; }
#define FUNC(name, op) \
 constexpr MInt name const { \
  MInt ret; \
  return ret.x= op, ret; \
 }
 FUNC(operator+(const MInt & r), B::md.plus(x, r.x))
 FUNC(operator-(const MInt & r), B::md.diff(x, r.x))
 FUNC(operator*(const MInt & r), B::md.mul(x, r.x))
 FUNC(pow(u64 k), math_internal::pow(x, k, B::md))
#undef FUNC
 constexpr MInt operator/(const MInt &r) const { return *this * r.inv(); }
 constexpr MInt &operator+=(const MInt &r) { return *this= *this + r; }
 constexpr MInt &operator-=(const MInt &r) { return *this= *this - r; }
 constexpr MInt &operator*=(const MInt &r) { return *this= *this * r; }
 constexpr MInt &operator/=(const MInt &r) { return *this= *this / r; }
 constexpr bool operator==(const MInt &r) const { return B::md.norm(x) == B::md.norm(r.x); }
 constexpr bool operator!=(const MInt &r) const { return !(*this == r); }
 constexpr bool operator<(const MInt &r) const { return B::md.norm(x) < B::md.norm(r.x); }
 constexpr inline MInt inv() const { return mod_inv<U>(val(), B::md.mod); }
 constexpr inline Uint val() const { return B::md.get(x); }
 friend ostream &operator<<(ostream &os, const MInt &r) { return os << r.val(); }
 friend istream &operator>>(istream &is, MInt &r) {
  i64 v;
  return is >> v, r= MInt(v), is;
 }
private:
 Uint x;
};
template <u64 MOD> using MP_B= conditional_t < (MOD < (1 << 30)) & MOD, MP_Mo32, conditional_t < MOD < (1ull << 32), MP_Na, conditional_t<(MOD < (1ull << 62)) & MOD, MP_Mo64, conditional_t<MOD<(1ull << 41), MP_Br, conditional_t<MOD<(1ull << 63), MP_D2B1_1, MP_D2B1_2>>>>>;
template <u64 MOD> using ModInt= MInt < conditional_t<MOD<(1 << 30), u32, u64>, SB<MP_B<MOD>, MOD>>;
}
using math_internal::ModInt;
#line 3 "src/LinearAlgebra/Matrix.hpp"
#include <vector>
#line 2 "src/LinearAlgebra/Vector.hpp"
#include <cstdint>
#line 4 "src/LinearAlgebra/Vector.hpp"
#include <valarray>
namespace _la_internal {
using namespace std;
template <class R> struct Vector {
 valarray<R> dat;
 Vector()= default;
 Vector(size_t n): dat(n) {}
 Vector(size_t n, const R &v): dat(v, n) {}
 Vector(const initializer_list<R> &v): dat(v) {}
 R &operator[](int i) { return dat[i]; }
 const R &operator[](int i) const { return dat[i]; }
 bool operator==(const Vector &r) const {
  if (dat.size() != r.dat.size()) return false;
  for (int i= dat.size(); i--;)
   if (dat[i] != r.dat[i]) return false;
  return true;
 }
 bool operator!=(const Vector &r) const { return !(*this == r); }
 explicit operator bool() const { return dat.size(); }
 Vector operator-() const { return Vector(dat.size())-= *this; }
 Vector &operator+=(const Vector &r) { return dat+= r.dat, *this; }
 Vector &operator-=(const Vector &r) { return dat-= r.dat, *this; }
 Vector &operator*=(const R &r) { return dat*= r, *this; }
 Vector operator+(const Vector &r) const { return Vector(*this)+= r; }
 Vector operator-(const Vector &r) const { return Vector(*this)-= r; }
 Vector operator*(const R &r) const { return Vector(*this)*= r; }
 size_t size() const { return dat.size(); }
 friend R dot(const Vector<R> &a, const Vector<R> &b) { return assert(a.size() == b.size()), (a.dat * b.dat).sum(); }
};
using u128= __uint128_t;
using u64= uint64_t;
using u8= uint8_t;
class Ref {
 u128 *ref;
 u8 i;
public:
 Ref(u128 *ref, u8 i): ref(ref), i(i) {}
 Ref &operator=(const Ref &r) { return *this= bool(r); }
 Ref &operator=(bool b) { return *ref&= ~(u128(1) << i), *ref|= u128(b) << i, *this; }
 Ref &operator|=(bool b) { return *ref|= u128(b) << i, *this; }
 Ref &operator&=(bool b) { return *ref&= ~(u128(!b) << i), *this; }
 Ref &operator^=(bool b) { return *ref^= u128(b) << i, *this; }
 operator bool() const { return (*ref >> i) & 1; }
};
template <> class Vector<bool> {
 size_t n;
public:
 valarray<u128> dat;
 Vector(): n(0) {}
 Vector(size_t n): n(n), dat((n + 127) >> 7) {}
 Vector(size_t n, bool b): n(n), dat(-u128(b), (n + 127) >> 7) {
  if (int k= n & 127; k) dat[dat.size() - 1]&= (u128(1) << k) - 1;
 }
 Vector(const initializer_list<bool> &v): n(v.size()), dat((n + 127) >> 7) {
  int i= 0;
  for (bool b: v) dat[i >> 7]|= u128(b) << (i & 127), ++i;
 }
 Ref operator[](int i) { return {begin(dat) + (i >> 7), u8(i & 127)}; }
 bool operator[](int i) const { return (dat[i >> 7] >> (i & 127)) & 1; }
 bool operator==(const Vector &r) const {
  if (dat.size() != r.dat.size()) return false;
  for (int i= dat.size(); i--;)
   if (dat[i] != r.dat[i]) return false;
  return true;
 }
 bool operator!=(const Vector &r) const { return !(*this == r); }
 explicit operator bool() const { return n; }
 Vector operator-() const { return Vector(*this); }
 Vector &operator+=(const Vector &r) { return dat^= r.dat, *this; }
 Vector &operator-=(const Vector &r) { return dat^= r.dat, *this; }
 Vector &operator*=(bool b) { return dat*= b, *this; }
 Vector operator+(const Vector &r) const { return Vector(*this)+= r; }
 Vector operator-(const Vector &r) const { return Vector(*this)-= r; }
 Vector operator*(bool b) const { return Vector(*this)*= b; }
 size_t size() const { return n; }
 friend bool dot(const Vector<bool> &a, const Vector<bool> &b) {
  assert(a.size() == b.size());
  u128 v= 0;
  for (int i= a.dat.size(); i--;) v^= a.dat[i] & b.dat[i];
  return __builtin_parityll(v >> 64) ^ __builtin_parityll(u64(v));
 }
};
template <class R> Vector<R> operator*(const R &r, const Vector<R> &v) { return v * r; }
template <class R> ostream &operator<<(ostream &os, const Vector<R> &v) {
 os << '[';
 for (int _= 0, __= v.size(); _ < __; ++_) os << (_ ? ", " : "") << v[_];
 return os << ']';
}
}
using _la_internal::Vector;
#line 5 "src/LinearAlgebra/Matrix.hpp"
namespace _la_internal {
template <class R, class D> struct Mat {
 Mat(): W(0) {}
 Mat(size_t h, size_t w): W(w), dat(h * w) {}
 Mat(size_t h, size_t w, R v): W(w), dat(v, h * w) {}
 Mat(initializer_list<initializer_list<R>> v): W(v.size() ? v.begin()->size() : 0), dat(v.size() * W) {
  auto it= begin(dat);
  for (const auto &r: v) {
   assert(r.size() == W);
   for (R x: r) *it++= x;
  }
 }
 size_t width() const { return W; }
 size_t height() const { return W ? dat.size() / W : 0; }
 auto operator[](int i) { return begin(dat) + i * W; }
 auto operator[](int i) const { return begin(dat) + i * W; }
protected:
 size_t W;
 valarray<R> dat;
 void add(const Mat &r) { assert(dat.size() == r.dat.size()), assert(W == r.W), dat+= r.dat; }
 D mul(const Mat &r) const {
  const size_t h= height(), w= r.W, l= W;
  assert(l == r.height());
  D ret(h, w);
  auto a= begin(dat);
  auto c= begin(ret.dat);
  for (int i= h; i--; c+= w) {
   auto b= begin(r.dat);
   for (int k= l; k--; ++a) {
    auto d= c;
    auto v= *a;
    for (int j= w; j--; ++b, ++d) *d+= v * *b;
   }
  }
  return ret;
 }
 Vector<R> mul(const Vector<R> &r) const {
  assert(W == r.size());
  const size_t h= height();
  Vector<R> ret(h);
  auto a= begin(dat);
  for (size_t i= 0; i < h; ++i)
   for (size_t k= 0; k < W; ++k, ++a) ret[i]+= *a * r[k];
  return ret;
 }
};
template <class D> struct Mat<bool, D> {
 struct Array {
  u128 *bg;
  Array(u128 *it): bg(it) {}
  Ref operator[](int i) { return Ref{bg + (i >> 7), u8(i & 127)}; }
  bool operator[](int i) const { return (bg[i >> 7] >> (i & 127)) & 1; }
 };
 struct ConstArray {
  const u128 *bg;
  ConstArray(const u128 *it): bg(it) {}
  bool operator[](int i) const { return (bg[i >> 7] >> (i & 127)) & 1; }
 };
 Mat(): H(0), W(0), m(0) {}
 Mat(size_t h, size_t w): H(h), W(w), m((w + 127) >> 7), dat(h * m) {}
 Mat(size_t h, size_t w, bool b): H(h), W(w), m((w + 127) >> 7), dat(-u128(b), h * m) {
  if (size_t i= h, k= w & 127; k)
   for (u128 s= (u128(1) << k) - 1; i--;) dat[i * m]&= s;
 }
 Mat(const initializer_list<initializer_list<bool>> &v): H(v.size()), W(H ? v.begin()->size() : 0), m((W + 127) >> 7), dat(H * m) {
  auto it= begin(dat);
  for (const auto &r: v) {
   assert(r.size() == W);
   int i= 0;
   for (bool b: r) it[i >> 7]|= u128(b) << (i & 127), ++i;
   it+= m;
  }
 }
 size_t width() const { return W; }
 size_t height() const { return H; }
 Array operator[](int i) { return {begin(dat) + i * m}; }
 ConstArray operator[](int i) const { return {begin(dat) + i * m}; }
 ConstArray get(int i) const { return {begin(dat) + i * m}; }
protected:
 size_t H, W, m;
 valarray<u128> dat;
 void add(const Mat &r) { assert(H == r.H), assert(W == r.W), dat^= r.dat; }
 D mul(const Mat &r) const {
  assert(W == r.H);
  D ret(H, r.W);
  valarray<u128> tmp(r.m << 8);
  auto y= begin(r.dat);
  for (size_t l= 0; l < W; l+= 8) {
   auto t= begin(tmp) + r.m;
   for (int i= 0, n= min<size_t>(8, W - l); i < n; ++i, y+= r.m) {
    auto u= begin(tmp);
    for (int s= 1 << i; s--;) {
     auto z= y;
     for (int j= r.m; j--; ++u, ++t, ++z) *t= *u ^ *z;
    }
   }
   auto a= begin(dat) + (l >> 7);
   auto c= begin(ret.dat);
   for (int i= H; i--; a+= m) {
    auto u= begin(tmp) + ((*a >> (l & 127)) & 255) * r.m;
    for (int j= r.m; j--; ++c, ++u) *c^= *u;
   }
  }
  return ret;
 }
 Vector<bool> mul(const Vector<bool> &r) const {
  assert(W == r.size());
  Vector<bool> ret(H);
  auto a= begin(dat);
  for (size_t i= 0; i < H; ++i) {
   u128 v= 0;
   for (size_t j= 0; j < m; ++j, ++a) v^= *a & r.dat[j];
   ret[i]= __builtin_parityll(v >> 64) ^ __builtin_parityll(u64(v));
  }
  return ret;
 }
};
template <class R> struct Matrix: public Mat<R, Matrix<R>> {
 using Mat<R, Matrix<R>>::Mat;
 explicit operator bool() const { return this->W; }
 static Matrix identity(int n) {
  Matrix ret(n, n);
  for (; n--;) ret[n][n]= R(true);
  return ret;
 }
 Matrix submatrix(const vector<int> &rows, const vector<int> &cols) const {
  Matrix ret(rows.size(), cols.size());
  for (int i= rows.size(); i--;)
   for (int j= cols.size(); j--;) ret[i][j]= (*this)[rows[i]][cols[j]];
  return ret;
 }
 Matrix submatrix_rm(vector<int> rows, vector<int> cols) const {
  sort(begin(rows), end(rows)), sort(begin(cols), end(cols)), rows.erase(unique(begin(rows), end(rows)), end(rows)), cols.erase(unique(begin(cols), end(cols)), end(cols));
  const int H= this->height(), W= this->width(), n= rows.size(), m= cols.size();
  vector<int> rs(H - n), cs(W - m);
  for (int i= 0, j= 0, k= 0; i < H; ++i)
   if (j < n && rows[j] == i) ++j;
   else rs[k++]= i;
  for (int i= 0, j= 0, k= 0; i < W; ++i)
   if (j < m && cols[j] == i) ++j;
   else cs[k++]= i;
  return submatrix(rs, cs);
 }
 bool operator==(const Matrix &r) const {
  if (this->width() != r.width() || this->height() != r.height()) return false;
  for (int i= this->dat.size(); i--;)
   if (this->dat[i] != r.dat[i]) return false;
  return true;
 }
 bool operator!=(const Matrix &r) const { return !(*this == r); }
 Matrix &operator*=(const Matrix &r) { return *this= this->mul(r); }
 Matrix operator*(const Matrix &r) const { return this->mul(r); }
 Matrix &operator*=(R r) { return this->dat*= r, *this; }
 template <class T> Matrix operator*(T r) const {
  static_assert(is_convertible_v<T, R>);
  return Matrix(*this)*= r;
 }
 Matrix &operator+=(const Matrix &r) { return this->add(r), *this; }
 Matrix operator+(const Matrix &r) const { return Matrix(*this)+= r; }
 Vector<R> operator*(const Vector<R> &r) const { return this->mul(r); }
 Vector<R> operator()(const Vector<R> &r) const { return this->mul(r); }
 Matrix pow(uint64_t k) const {
  size_t W= this->width();
  assert(W == this->height());
  for (Matrix ret= identity(W), b= *this;; b*= b)
   if (k & 1 ? ret*= b, !(k>>= 1) : !(k>>= 1)) return ret;
 }
};
template <class R, class T> Matrix<R> operator*(const T &r, const Matrix<R> &m) { return m * r; }
template <class R> ostream &operator<<(ostream &os, const Matrix<R> &m) {
 os << "\n[";
 for (int i= 0, h= m.height(); i < h; os << ']', ++i) {
  if (i) os << "\n ";
  os << '[';
  for (int j= 0, w= m.width(); j < w; ++j) os << (j ? ", " : "") << m[i][j];
 }
 return os << ']';
}
template <class K> static bool is_zero(K x) {
 if constexpr (is_floating_point_v<K>) return abs(x) < 1e-8;
 else return x == K();
}
}
using _la_internal::Matrix;
#line 4 "src/Internal/ListRange.hpp"
#include <iterator>
#line 6 "src/Internal/ListRange.hpp"
#define _LR(name, IT, CT) \
 template <class T> struct name { \
  using Iterator= typename std::vector<T>::IT; \
  Iterator bg, ed; \
  Iterator begin() const { return bg; } \
  Iterator end() const { return ed; } \
  size_t size() const { return std::distance(bg, ed); } \
  CT &operator[](int i) const { return bg[i]; } \
 }
_LR(ListRange, iterator, T);
_LR(ConstListRange, const_iterator, const T);
#undef _LR
template <class T> struct CSRArray {
 std::vector<T> dat;
 std::vector<int> p;
 size_t size() const { return p.size() - 1; }
 ListRange<T> operator[](int i) { return {dat.begin() + p[i], dat.begin() + p[i + 1]}; }
 ConstListRange<T> operator[](int i) const { return {dat.cbegin() + p[i], dat.cbegin() + p[i + 1]}; }
};
template <template <class> class F, class T> std::enable_if_t<std::disjunction_v<std::is_same<F<T>, ListRange<T>>, std::is_same<F<T>, ConstListRange<T>>, std::is_same<F<T>, CSRArray<T>>>, std::ostream &> operator<<(std::ostream &os, const F<T> &r) {
 os << '[';
 for (int _= 0, __= r.size(); _ < __; ++_) os << (_ ? ", " : "") << r[_];
 return os << ']';
}
#line 3 "src/Graph/Graph.hpp"
struct Edge: std::pair<int, int> {
 using std::pair<int, int>::pair;
 Edge &operator--() { return --first, --second, *this; }
 int to(int v) const { return first ^ second ^ v; }
 friend std::istream &operator>>(std::istream &is, Edge &e) { return is >> e.first >> e.second, is; }
};
struct Graph: std::vector<Edge> {
 size_t n;
 Graph(size_t n= 0, size_t m= 0): vector(m), n(n) {}
 size_t vertex_size() const { return n; }
 size_t edge_size() const { return size(); }
 size_t add_vertex() { return n++; }
 size_t add_edge(int s, int d) { return emplace_back(s, d), size() - 1; }
 size_t add_edge(Edge e) { return emplace_back(e), size() - 1; }
#define _ADJ_FOR(a, b) \
 for (auto [u, v]: *this) a; \
 for (size_t i= 0; i < n; ++i) p[i + 1]+= p[i]; \
 for (int i= size(); i--;) { \
  auto [u, v]= (*this)[i]; \
  b; \
 }
#define _ADJ(a, b) \
 vector<int> p(n + 1), c(size() << !dir); \
 if (!dir) { \
  _ADJ_FOR((++p[u], ++p[v]), (c[--p[u]]= a, c[--p[v]]= b)) \
 } else if (dir > 0) { \
  _ADJ_FOR(++p[u], c[--p[u]]= a) \
 } else { \
  _ADJ_FOR(++p[v], c[--p[v]]= b) \
 } \
 return {c, p}
 CSRArray<int> adjacency_vertex(int dir) const { _ADJ(v, u); }
 CSRArray<int> adjacency_edge(int dir) const { _ADJ(i, i); }
#undef _ADJ
#undef _ADJ_FOR
};
#line 2 "src/Graph/HeavyLightDecomposition.hpp"
#include <array>
#line 5 "src/Graph/HeavyLightDecomposition.hpp"
class HeavyLightDecomposition {
 std::vector<int> P, PP, D, I, L, R;
public:
 HeavyLightDecomposition()= default;
 HeavyLightDecomposition(const Graph &g, int root= 0): HeavyLightDecomposition(g.adjacency_vertex(0), root) {}
 HeavyLightDecomposition(const CSRArray<int> &adj, int root= 0) {
  const int n= adj.size();
  P.assign(n, -2), PP.resize(n), D.resize(n), I.resize(n), L.resize(n), R.resize(n);
  auto f= [&, i= 0, v= 0, t= 0](int r) mutable {
   for (P[r]= -1, I[t++]= r; i < t; ++i)
    for (int u: adj[v= I[i]])
     if (P[v] != u) P[I[t++]= u]= v;
  };
  f(root);
  for (int r= 0; r < n; ++r)
   if (P[r] == -2) f(r);
  std::vector<int> Z(n, 1), nx(n, -1);
  for (int i= n, v; i--;) {
   if (P[v= I[i]] == -1) continue;
   if (Z[P[v]]+= Z[v]; nx[P[v]] == -1) nx[P[v]]= v;
   if (Z[nx[P[v]]] < Z[v]) nx[P[v]]= v;
  }
  for (int v= n; v--;) PP[v]= v;
  for (int v: I)
   if (nx[v] != -1) PP[nx[v]]= v;
  for (int v: I)
   if (P[v] != -1) PP[v]= PP[PP[v]], D[v]= D[P[v]] + 1;
  for (int i= n; i--;) L[I[i]]= i;
  for (int v: I) {
   int ir= R[v]= L[v] + Z[v];
   for (int u: adj[v])
    if (u != P[v] && u != nx[v]) L[u]= (ir-= Z[u]);
   if (nx[v] != -1) L[nx[v]]= L[v] + 1;
  }
  for (int i= n; i--;) I[L[i]]= i;
 }
 int to_seq(int v) const { return L[v]; }
 int to_vertex(int i) const { return I[i]; }
 size_t size() const { return P.size(); }
 int parent(int v) const { return P[v]; }
 int head(int v) const { return PP[v]; }
 int root(int v) const {
  for (v= PP[v];; v= PP[P[v]])
   if (P[v] == -1) return v;
 }
 bool connected(int u, int v) const { return root(u) == root(v); }
 // u is in v
 bool in_subtree(int u, int v) const { return L[v] <= L[u] && L[u] < R[v]; }
 int subtree_size(int v) const { return R[v] - L[v]; }
 int lca(int u, int v) const {
  for (;; v= P[PP[v]]) {
   if (L[u] > L[v]) std::swap(u, v);
   if (PP[u] == PP[v]) return u;
  }
 }
 int la(int v, int k) const {
  assert(k <= D[v]);
  for (int u;; k-= L[v] - L[u] + 1, v= P[u])
   if (L[v] - k >= L[u= PP[v]]) return I[L[v] - k];
 }
 int jump(int u, int v, int k) const {
  if (!k) return u;
  if (u == v) return -1;
  if (k == 1) return in_subtree(v, u) ? la(v, D[v] - D[u] - 1) : P[u];
  int w= lca(u, v), d_uw= D[u] - D[w], d_vw= D[v] - D[w];
  return k > d_uw + d_vw ? -1 : k <= d_uw ? la(u, k) : la(v, d_uw + d_vw - k);
 }
 int depth(int v) const { return D[v]; }
 int dist(int u, int v) const { return D[u] + D[v] - D[lca(u, v)] * 2; }
 // half-open interval [l,r)
 std::pair<int, int> subtree(int v) const { return {L[v], R[v]}; }
 // sequence of closed intervals [l,r]
 std::vector<std::pair<int, int>> path(int u, int v, bool edge= 0) const {
  std::vector<std::pair<int, int>> up, down;
  while (PP[u] != PP[v]) {
   if (L[u] < L[v]) down.emplace_back(L[PP[v]], L[v]), v= P[PP[v]];
   else up.emplace_back(L[u], L[PP[u]]), u= P[PP[u]];
  }
  if (L[u] < L[v]) down.emplace_back(L[u] + edge, L[v]);
  else if (L[v] + edge <= L[u]) up.emplace_back(L[u], L[v] + edge);
  return up.insert(up.end(), down.rbegin(), down.rend()), up;
 }
};
#line 4 "src/Graph/Rerooting.hpp"
// put_edge(int v, int e, T t) -> U
// op(U l, U r) -> U
// ui(:U) is the identity element of op
// put_vertex(int v, U sum) -> T
template <class T> class Rerooting {
 HeavyLightDecomposition hld;
 std::valarray<T> dp, dp1, dp2;
public:
 template <class U, class F1, class F2, class F3> Rerooting(const Graph &g, const CSRArray<int> &adje, const HeavyLightDecomposition &hld, const F1 &put_edge, const F2 &op, const U &ui, const F3 &put_vertex) : hld(hld){
  static_assert(std::is_invocable_r_v<U, F1, int, int, T>, "put_edge(int,int,T) is not invocable");
  static_assert(std::is_invocable_r_v<U, F2, U, U>, "op(U,U) is not invocable");
  static_assert(std::is_invocable_r_v<T, F3, int, U>, "put_vertex(int,U) is not invocable");
  const int n= g.vertex_size();
  dp.resize(n), dp1.resize(n), dp2.resize(n);
  for (int i= n, v; i--;) {
   U sum= ui;
   for (int e: adje[v= hld.to_vertex(i)])
    if (int u= g[e].to(v); u != hld.parent(v)) sum= op(sum, put_edge(v, e, dp1[u]));
   dp1[v]= put_vertex(v, sum);
  }
  for (int i= 0, v; i < n; ++i) {
   auto gv= adje[v= hld.to_vertex(i)];
   int dg= gv.size();
   std::valarray<U> f(dg + 1), b(dg + 1);
   for (int j= 0, e, u; j < dg; ++j) u= g[e= gv[j]].to(v), f[j + 1]= put_edge(v, e, u == hld.parent(v) ? dp2[v] : dp1[u]);
   f[0]= b[dg]= ui;
   for (int j= dg; j--;) b[j]= op(f[j + 1], b[j + 1]);
   for (int j= 0; j < dg; ++j) f[j + 1]= op(f[j], f[j + 1]);
   for (int j= 0; j < dg; ++j)
    if (int u= g[gv[j]].to(v); u != hld.parent(v)) dp2[u]= put_vertex(v, op(f[j], b[j + 1]));
   dp[v]= put_vertex(v, f[dg]);
  }
 }
 template <class U, class F1, class F2, class F3> Rerooting(const Graph &g, const CSRArray<int> &adje, const F1 &put_edge, const F2 &op, const U &ui, const F3 &put_vertex): Rerooting(g, adje, HeavyLightDecomposition(g), put_edge, op, ui, put_vertex) {}
 template <class U, class F1, class F2, class F3> Rerooting(const Graph &g, const HeavyLightDecomposition &hld, const F1 &put_edge, const F2 &op, const U &ui, const F3 &put_vertex): Rerooting(g, g.adjacency_edge(0), hld, put_edge, op, ui, put_vertex) {}
 template <class U, class F1, class F2, class F3> Rerooting(const Graph &g, const F1 &put_edge, const F2 &op, const U &ui, const F3 &put_vertex): Rerooting(g, g.adjacency_edge(0), HeavyLightDecomposition(g), put_edge, op, ui, put_vertex) {}
 const T &operator[](int v) const { return dp[v]; }
 auto begin() const { return std::cbegin(dp); }
 auto end() const { return std::cend(dp); }
 const T &operator()(int root, int v) const { return root == v ? dp[v] : hld.in_subtree(root, v) ? dp2[hld.jump(v, root, 1)] : dp1[v]; }
};
#line 10 "test/loj/3350.test.cpp"
using namespace std;
signed main() {
 cin.tie(0);
 ios::sync_with_stdio(0);
 using Mint= ModInt<int(1e9 + 7)>;
 using Mat= Matrix<Mint>;
 long long N, D;
 cin >> N >> D;
 Graph g(N, N - 1);
 for (auto &e: g) cin >> e, --e;
 auto put_edge= [](int, int, Mat x) {
  swap(x[0][0], x[1][0]);
  swap(x[0][1], x[1][1]);
  return x;
 };
 auto op= [](const Mat &l, const Mat &r) {
  Mat ret(2, 2);
  for (int i= 2; i--;)
   for (int j= 2; j--;) {
    ret[i & j][1]+= l[i][1] * r[j][0] + l[i][0] * r[j][1];
    ret[i & j][0]+= l[i][0] * r[j][0];
   }
  return ret;
 };
 Mat ui(2, 2);
 ui[1][0]= 1;
 auto put_vertex= [](int, Mat x) {
  x[0][1]+= 1;
  return x;
 };
 Rerooting<Mat> dp(g, put_edge, op, ui, put_vertex);
 Mat sum(2, 2);
 for (int i= N; i--;) sum+= dp[i];
 auto M= sum;
 M[0][0]*= N, M[1][0]*= N;
 auto A= dp[0];
 A[0][0]*= N, A[1][0]*= N;
 Mint ans= (A * M.pow(D - 1) * sum)[0][0];
 cout << ans << '\n';
 return 0;
}

Test cases

Env	Name	Status	Elapsed	Memory
g++-13	000	AC	5 ms	4 MB
g++-13	001	AC	5 ms	4 MB
g++-13	002	AC	4 ms	4 MB
g++-13	003	AC	4 ms	4 MB
g++-13	005	AC	4 ms	3 MB
g++-13	006	AC	4 ms	4 MB
g++-13	007	AC	4 ms	4 MB
g++-13	008	AC	4 ms	4 MB
g++-13	009	AC	4 ms	4 MB
g++-13	010	AC	4 ms	4 MB
g++-13	011	AC	4 ms	4 MB
g++-13	012	AC	5 ms	4 MB
g++-13	013	AC	5 ms	4 MB
g++-13	014	AC	5 ms	4 MB
g++-13	015	AC	5 ms	4 MB
g++-13	016	AC	5 ms	4 MB
g++-13	017	AC	124 ms	26 MB
g++-13	018	AC	123 ms	26 MB
g++-13	019	AC	124 ms	32 MB
g++-13	020	AC	123 ms	26 MB
g++-13	021	AC	121 ms	26 MB
g++-13	022	AC	6 ms	4 MB
g++-13	023	AC	5 ms	4 MB
g++-13	024	AC	5 ms	4 MB
g++-13	025	AC	5 ms	4 MB
g++-13	026	AC	5 ms	4 MB
g++-13	027	AC	125 ms	26 MB
g++-13	028	AC	107 ms	24 MB
g++-13	029	AC	105 ms	29 MB
g++-13	030	AC	122 ms	26 MB
g++-13	031	AC	124 ms	26 MB
g++-13	032	AC	118 ms	26 MB
g++-13	033	AC	118 ms	26 MB
g++-13	034	AC	98 ms	26 MB
g++-13	035	AC	116 ms	26 MB
g++-13	036	AC	119 ms	26 MB
g++-13	037	AC	118 ms	26 MB
g++-13	038	AC	119 ms	26 MB
g++-13	039	AC	119 ms	26 MB
clang++-18	000	AC	5 ms	4 MB
clang++-18	001	AC	5 ms	4 MB
clang++-18	002	AC	4 ms	4 MB
clang++-18	003	AC	4 ms	4 MB
clang++-18	005	AC	4 ms	4 MB
clang++-18	006	AC	4 ms	4 MB
clang++-18	007	AC	4 ms	4 MB
clang++-18	008	AC	4 ms	4 MB
clang++-18	009	AC	4 ms	4 MB
clang++-18	010	AC	4 ms	4 MB
clang++-18	011	AC	4 ms	4 MB
clang++-18	012	AC	5 ms	4 MB
clang++-18	013	AC	5 ms	4 MB
clang++-18	014	AC	5 ms	4 MB
clang++-18	015	AC	5 ms	4 MB
clang++-18	016	AC	5 ms	4 MB
clang++-18	017	AC	112 ms	26 MB
clang++-18	018	AC	110 ms	26 MB
clang++-18	019	AC	114 ms	32 MB
clang++-18	020	AC	113 ms	26 MB
clang++-18	021	AC	114 ms	26 MB
clang++-18	022	AC	6 ms	4 MB
clang++-18	023	AC	5 ms	4 MB
clang++-18	024	AC	5 ms	4 MB
clang++-18	025	AC	5 ms	4 MB
clang++-18	026	AC	5 ms	4 MB
clang++-18	027	AC	115 ms	26 MB
clang++-18	028	AC	99 ms	24 MB
clang++-18	029	AC	106 ms	28 MB
clang++-18	030	AC	115 ms	26 MB
clang++-18	031	AC	114 ms	26 MB
clang++-18	032	AC	114 ms	26 MB
clang++-18	033	AC	111 ms	26 MB
clang++-18	034	AC	93 ms	26 MB
clang++-18	035	AC	114 ms	26 MB
clang++-18	036	AC	126 ms	26 MB
clang++-18	037	AC	124 ms	26 MB
clang++-18	038	AC	125 ms	26 MB
clang++-18	039	AC	117 ms	26 MB