Problem p02728 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstring>
#include <deque>
#include <fstream>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <vector>
using namespace std;
using ll = long long;
#define fst first
#define snd second

/* clang-format off */
template <class T, size_t D> struct _vec { using type = vector<typename _vec<T, D - 1>::type>; };
template <class T> struct _vec<T, 0> { using type = T; };
template <class T, size_t D> using vec = typename _vec<T, D>::type;
template <class T> vector<T> make_v(size_t size, const T& init) { return vector<T>(size, init); }
template <class... Ts> auto make_v(size_t size, Ts... rest) { return vector<decltype(make_v(rest...))>(size, make_v(rest...)); }
template <class T> inline void chmin(T &a, const T& b) { if (b < a) a = b; }
template <class T> inline void chmax(T &a, const T& b) { if (b > a) a = b; }
/* clang-format on */

template <std::uint_fast64_t Modulus> class modint {
  using u64 = std::uint_fast64_t;

public:
  u64 a;

  constexpr modint(const u64 x = 0) noexcept : a(x % Modulus) {}
  constexpr u64 &value() noexcept { return a; }
  constexpr const u64 &value() const noexcept { return a; }
  constexpr modint operator+(const modint rhs) const noexcept {
    return modint(*this) += rhs;
  }
  constexpr modint operator-(const modint rhs) const noexcept {
    return modint(*this) -= rhs;
  }
  constexpr modint operator*(const modint rhs) const noexcept {
    return modint(*this) *= rhs;
  }
  constexpr modint operator/(const modint rhs) const noexcept {
    return modint(*this) /= rhs;
  }
  constexpr modint &operator+=(const modint rhs) noexcept {
    a += rhs.a;
    if (a >= Modulus) {
      a -= Modulus;
    }
    return *this;
  }
  constexpr modint &operator-=(const modint rhs) noexcept {
    if (a < rhs.a) {
      a += Modulus;
    }
    a -= rhs.a;
    return *this;
  }
  constexpr modint &operator*=(const modint rhs) noexcept {
    a = a * rhs.a % Modulus;
    return *this;
  }
  constexpr modint &operator/=(const modint rhs) noexcept {
    return *this *= ~rhs;
  }
  constexpr modint power(u64 exp) const noexcept {
    modint v = 1, x = *this;
    while (exp) {
      if (exp & 1) {
        v *= x;
      }
      x *= x;
      exp >>= 1;
    }
    return v;
  }
  constexpr modint operator~() const noexcept { return power(Modulus - 2); }
};

using mint = modint<1000000007>;

template <typename Data, typename T> struct ReRooting {

  struct Node {
    int to, rev;
    Data data;
  };

  using F1 = function<T(T, T)>;
  using F2 = function<T(T, Data)>;

  vector<vector<Node>> g;
  vector<vector<T>> ldp, rdp;
  vector<int> lptr, rptr;
  const F1 f1;
  const F2 f2;
  const T ident;

  ReRooting(int n, const F1 &f1, const F2 &f2, const T &ident)
      : g(n), ldp(n), rdp(n), lptr(n), rptr(n), f1(f1), f2(f2), ident(ident) {}

  void add_edge(int u, int v, const Data &d) {
    g[u].emplace_back((Node){v, (int)g[v].size(), d});
    g[v].emplace_back((Node){u, (int)g[u].size() - 1, d});
  }

  void add_edge_bi(int u, int v, const Data &d, const Data &e) {
    g[u].emplace_back((Node){v, (int)g[v].size(), d});
    g[v].emplace_back((Node){u, (int)g[u].size() - 1, e});
  }

  T dfs(int idx, int par) {

    while (lptr[idx] != par && lptr[idx] < g[idx].size()) {
      auto &e = g[idx][lptr[idx]];
      ldp[idx][lptr[idx] + 1] =
          f1(ldp[idx][lptr[idx]], f2(dfs(e.to, e.rev), e.data));
      ++lptr[idx];
    }
    while (rptr[idx] != par && rptr[idx] >= 0) {
      auto &e = g[idx][rptr[idx]];
      rdp[idx][rptr[idx]] =
          f1(rdp[idx][rptr[idx] + 1], f2(dfs(e.to, e.rev), e.data));
      --rptr[idx];
    }
    if (par < 0)
      return rdp[idx][0];
    return f1(ldp[idx][par], rdp[idx][par + 1]);
  }

  vector<T> solve() {
    for (int i = 0; i < g.size(); i++) {
      ldp[i].assign(g[i].size() + 1, ident);
      rdp[i].assign(g[i].size() + 1, ident);
      lptr[i] = 0;
      rptr[i] = (int)g[i].size() - 1;
    }
    vector<T> ret;
    for (int i = 0; i < g.size(); i++) {
      ret.push_back(dfs(i, -1));
    }
    return ret;
  }
};

vector<mint> fact, factInv;
void initFact(int N) {
  fact.resize(N + 1);
  factInv.resize(N + 1);
  fact[0] = 1;
  for (int i = 1; i <= N; i++)
    fact[i] = fact[i - 1] * i;
  factInv[N] = ~fact[N];
  for (int i = N - 1; i >= 0; i--)
    factInv[i] = factInv[i + 1] * (i + 1);
}

mint choose(int n, int k) {
  if (n < 0 || k < 0 || k > n) {
    return 0;
  } else {
    return fact[n] * factInv[k] * factInv[n - k];
  }
}

int main() {
#ifdef DEBUG
  ifstream ifs("in.txt");
  cin.rdbuf(ifs.rdbuf());
#endif
  int N;
  while (cin >> N) {
    initFact((int)1e5 + 10);
    using P = pair<int, mint>;
    auto f1 = [&](const P &a, const P &b) -> P {
      mint x = a.snd;
      mint y = b.snd;
      return {a.fst + b.fst, a.snd * b.snd * choose(a.fst + b.fst, a.fst)};
    };
    auto f2 = [&](const P &a, int d) -> P { return {a.fst + 1, a.snd}; };
    ReRooting<int, P> g(N, f1, f2, {0, mint(1)});
    for (int i = 0; i < N - 1; i++) {
      int a, b;
      cin >> a >> b;
      --a;
      --b;
      g.add_edge(a, b, 0);
    }
    for (auto &x : g.solve()) {
      cout << x.snd.value() << endl;
    }
  }
  return 0;
}


Fixed submission:
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstring>
#include <deque>
#include <fstream>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <vector>
using namespace std;
using ll = long long;
#define fst first
#define snd second

/* clang-format off */
template <class T, size_t D> struct _vec { using type = vector<typename _vec<T, D - 1>::type>; };
template <class T> struct _vec<T, 0> { using type = T; };
template <class T, size_t D> using vec = typename _vec<T, D>::type;
template <class T> vector<T> make_v(size_t size, const T& init) { return vector<T>(size, init); }
template <class... Ts> auto make_v(size_t size, Ts... rest) { return vector<decltype(make_v(rest...))>(size, make_v(rest...)); }
template <class T> inline void chmin(T &a, const T& b) { if (b < a) a = b; }
template <class T> inline void chmax(T &a, const T& b) { if (b > a) a = b; }
/* clang-format on */

template <std::uint_fast64_t Modulus> class modint {
  using u64 = std::uint_fast64_t;

public:
  u64 a;

  constexpr modint(const u64 x = 0) noexcept : a(x % Modulus) {}
  constexpr u64 &value() noexcept { return a; }
  constexpr const u64 &value() const noexcept { return a; }
  constexpr modint operator+(const modint rhs) const noexcept {
    return modint(*this) += rhs;
  }
  constexpr modint operator-(const modint rhs) const noexcept {
    return modint(*this) -= rhs;
  }
  constexpr modint operator*(const modint rhs) const noexcept {
    return modint(*this) *= rhs;
  }
  constexpr modint operator/(const modint rhs) const noexcept {
    return modint(*this) /= rhs;
  }
  constexpr modint &operator+=(const modint rhs) noexcept {
    a += rhs.a;
    if (a >= Modulus) {
      a -= Modulus;
    }
    return *this;
  }
  constexpr modint &operator-=(const modint rhs) noexcept {
    if (a < rhs.a) {
      a += Modulus;
    }
    a -= rhs.a;
    return *this;
  }
  constexpr modint &operator*=(const modint rhs) noexcept {
    a = a * rhs.a % Modulus;
    return *this;
  }
  constexpr modint &operator/=(const modint rhs) noexcept {
    return *this *= ~rhs;
  }
  constexpr modint power(u64 exp) const noexcept {
    modint v = 1, x = *this;
    while (exp) {
      if (exp & 1) {
        v *= x;
      }
      x *= x;
      exp >>= 1;
    }
    return v;
  }
  constexpr modint operator~() const noexcept { return power(Modulus - 2); }
};

using mint = modint<1000000007>;

template <typename Data, typename T> struct ReRooting {

  struct Node {
    int to, rev;
    Data data;
  };

  using F1 = function<T(T, T)>;
  using F2 = function<T(T, Data)>;

  vector<vector<Node>> g;
  vector<vector<T>> ldp, rdp;
  vector<int> lptr, rptr;
  const F1 f1;
  const F2 f2;
  const T ident;

  ReRooting(int n, const F1 &f1, const F2 &f2, const T &ident)
      : g(n), ldp(n), rdp(n), lptr(n), rptr(n), f1(f1), f2(f2), ident(ident) {}

  void add_edge(int u, int v, const Data &d) {
    g[u].emplace_back((Node){v, (int)g[v].size(), d});
    g[v].emplace_back((Node){u, (int)g[u].size() - 1, d});
  }

  void add_edge_bi(int u, int v, const Data &d, const Data &e) {
    g[u].emplace_back((Node){v, (int)g[v].size(), d});
    g[v].emplace_back((Node){u, (int)g[u].size() - 1, e});
  }

  T dfs(int idx, int par) {

    while (lptr[idx] != par && lptr[idx] < g[idx].size()) {
      auto &e = g[idx][lptr[idx]];
      ldp[idx][lptr[idx] + 1] =
          f1(ldp[idx][lptr[idx]], f2(dfs(e.to, e.rev), e.data));
      ++lptr[idx];
    }
    while (rptr[idx] != par && rptr[idx] >= 0) {
      auto &e = g[idx][rptr[idx]];
      rdp[idx][rptr[idx]] =
          f1(rdp[idx][rptr[idx] + 1], f2(dfs(e.to, e.rev), e.data));
      --rptr[idx];
    }
    if (par < 0)
      return rdp[idx][0];
    return f1(ldp[idx][par], rdp[idx][par + 1]);
  }

  vector<T> solve() {
    for (int i = 0; i < g.size(); i++) {
      ldp[i].assign(g[i].size() + 1, ident);
      rdp[i].assign(g[i].size() + 1, ident);
      lptr[i] = 0;
      rptr[i] = (int)g[i].size() - 1;
    }
    vector<T> ret;
    for (int i = 0; i < g.size(); i++) {
      ret.push_back(dfs(i, -1));
    }
    return ret;
  }
};

vector<mint> fact, factInv;
void initFact(int N) {
  fact.resize(N + 1);
  factInv.resize(N + 1);
  fact[0] = 1;
  for (int i = 1; i <= N; i++)
    fact[i] = fact[i - 1] * i;
  factInv[N] = ~fact[N];
  for (int i = N - 1; i >= 0; i--)
    factInv[i] = factInv[i + 1] * (i + 1);
}

mint choose(int n, int k) {
  if (n < 0 || k < 0 || k > n) {
    return 0;
  } else {
    return fact[n] * factInv[k] * factInv[n - k];
  }
}

int main() {
#ifdef DEBUG
  ifstream ifs("in.txt");
  cin.rdbuf(ifs.rdbuf());
#endif
  int N;
  while (cin >> N) {
    initFact((int)2 * 1e5 + 10);
    using P = pair<int, mint>;
    auto f1 = [&](const P &a, const P &b) -> P {
      mint x = a.snd;
      mint y = b.snd;
      return {a.fst + b.fst, a.snd * b.snd * choose(a.fst + b.fst, a.fst)};
    };
    auto f2 = [&](const P &a, int d) -> P { return {a.fst + 1, a.snd}; };
    ReRooting<int, P> g(N, f1, f2, {0, mint(1)});
    for (int i = 0; i < N - 1; i++) {
      int a, b;
      cin >> a >> b;
      --a;
      --b;
      g.add_edge(a, b, 0);
    }
    for (auto &x : g.solve()) {
      cout << x.snd.value() << endl;
    }
  }
  return 0;
}