Problem p02728 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using VI = vector<int>;
using VL = vector<ll>;
using VVI = vector<vector<int>>;
using VVL = vector<vector<ll>>;
using PII = std::pair<int, int>;
using PLL = std::pair<ll, ll>;

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n)-1; i >= 0; i--)
#define rep2(i, s, n) for (int i = (s); i < (int)(n); i++)
#define rep3(i, s, n, d) for (int i = (s); i < (int)(n); i += (d))
#define allpt(v) (v).begin(), (v).end()
#define allpt_c(v) (v).cbegin(), (v).cend()
#define allpt_r(v) (v).rbegin(), (v).rend()

const int mod = 1e9 + 7;

const string wsp = " ";
const string tb = "\t";
const string rt = "\n";

template <typename T> void show1dvec(const vector<T> &v) {
  if (v.size() == 0)
    return;
  int n = v.size() - 1;
  rep(i, n) cout << v[i] << wsp;
  cout << v[n];
  return;
}

template <typename T> void show2dvec(const vector<vector<T>> &v) {
  int n = v.size();
  rep(i, n) show1dvec(v[i]);
}

template <typename T, typename S> void show1dpair(const vector<pair<T, S>> &v) {
  int n = v.size();
  rep(i, n) cout << v[i].first << wsp << v[i].second << rt;
  return;
}

template <typename T, typename S>
void pairzip(const vector<pair<T, S>> &v, vector<T> &t, vector<T> &s) {
  int n = v.size();
  rep(i, n) {
    t.push_back(v[i].first);
    s.push_back(v[i].second);
  }
  return;
}

template <typename T> void maxvec(vector<T> &v) {
  T s = v[0];
  int n = v.size();
  rep(i, n - 1) {
    if (s > v[i + 1]) {
      v[i + 1] = s;
    }
    s = v[i + 1];
  }
}

template <typename T, typename S> bool myfind(T t, S s) {
  return find(t.cbegin(), t.cend(), s) != t.cend();
}

bool check(int y, int x, int h, int w) {
  return 0 <= y && y < h && 0 <= x && x < w;
}

VI cumsum(VI &v) {
  int s = 0;
  VI ret = {0};

  rep(i, v.size()) {
    s += v[i];
    ret.push_back(s);
  }
  return ret;
}

void shuffle(VI &v, int t) {
  int temp = v[t - 1];
  rep(i, t - 1) v[t - 1 - i] = v[t - 2 - i];
  v[0] = temp;
}

struct node {
  VI children;
  ll ans = 1;
  ll ans_from_subtree = 1;
  ll ans_from_surtree = 1;
  int parent = -1;
  int subtree_size = 1;
  int surtree_size = 1;
};

void printsubtree(node n) {
  cout << "parent = " << n.parent << rt;
  cout << "children = ";
  show1dvec(n.children);
  cout << rt;
  cout << "subtree_size = " << n.subtree_size << rt;
  cout << "surtree_size = " << n.surtree_size << rt;
  cout << "ans_from_subtree = " << n.ans_from_subtree << rt;
  cout << "ans_from_surtree = " << n.ans_from_surtree << rt;
  cout << "ans = " << n.ans << rt;
  cout << rt;
}

ll pow_mod(int p, int q, int mod) {
  ll ret = 1, r = p;
  while (q) {
    if (q % 2)
      ret *= r, ret %= mod;
    r = (r * r) % mod, q /= 2;
  }
  return ret % mod;
}

ll const nmax = 100001;
VL frac_table(nmax, 1);
VL frac_inv_table(nmax, 1);

void dfs(const int &x, const VVI &connect, vector<node> &nodes) {
  for (auto z : connect[x]) {
    if (z != nodes[x].parent) {
      nodes[z].parent = x;
      nodes[x].children.push_back(z);
      dfs(z, connect, nodes);
    }
  }
}

void dfs2(const int &x, const int &n, const VVI &connect, vector<node> &nodes) {
  for (auto &z : nodes[x].children) {
    dfs2(z, n, connect, nodes);
    nodes[x].subtree_size += nodes[z].subtree_size;

    nodes[x].ans_from_subtree *= frac_inv_table[nodes[z].subtree_size];
    nodes[x].ans_from_subtree %= mod;
    nodes[x].ans_from_subtree *= nodes[z].ans_from_subtree;
    nodes[x].ans_from_subtree %= mod;
  }
  nodes[x].surtree_size = n - nodes[x].subtree_size;
  nodes[x].ans_from_subtree *= frac_table[nodes[x].subtree_size - 1];
  nodes[x].ans_from_subtree %= mod;
}

void dfs3(const int &x, const int &n, VVI &connect, vector<node> &nodes) {
  nodes[x].ans = nodes[x].ans_from_subtree;
  if (nodes[x].parent != -1) {
    nodes[x].ans *= frac_table[n - 1];
    nodes[x].ans %= mod;
    nodes[x].ans *= frac_inv_table[nodes[x].surtree_size];
    nodes[x].ans %= mod;
    nodes[x].ans *= frac_inv_table[nodes[x].subtree_size - 1];
    nodes[x].ans %= mod;
    nodes[x].ans *= nodes[x].ans_from_surtree;
    nodes[x].ans %= mod;
  }
  for (auto z : nodes[x].children) {
    nodes[z].ans_from_surtree *= nodes[x].ans;
    nodes[z].ans_from_surtree *= frac_inv_table[n - 1];
    nodes[z].ans_from_surtree %= mod;
    nodes[z].ans_from_surtree *= frac_table[nodes[z].subtree_size];
    nodes[z].ans_from_surtree %= mod;
    nodes[z].ans_from_surtree *= frac_table[n - 1 - nodes[z].subtree_size];
    nodes[z].ans_from_surtree %= mod;
    nodes[z].ans_from_surtree *=
        pow_mod(nodes[z].ans_from_subtree, mod - 2, mod);
    nodes[z].ans_from_surtree %= mod;

    dfs3(z, n, connect, nodes);
  }
}

int main() {

#ifdef DEBUG
  cout << "DEBUG MODE" << endl;
  ifstream in("input.txt"); // for debug
  cin.rdbuf(in.rdbuf());    // for debug
#endif

  int s = 1, t = 1;
  rep2(i, 1, nmax) {
    frac_table[i] = (frac_table[i - 1] * i) % mod;
    frac_inv_table[i] =
        (frac_inv_table[i - 1] * pow_mod(i, mod - 2, mod)) % mod;
  }

  int n, a, b;
  cin >> n;
  VVI connect(n);
  vector<node> nodes(n);
  rep(i, n - 1) {
    cin >> a >> b;
    a--, b--;
    connect[a].push_back(b);
    connect[b].push_back(a);
  }

  dfs(0, connect, nodes);
  dfs2(0, n, connect, nodes);
  dfs3(0, n, connect, nodes);
  // for_each(allpt(nodes), printsubtree);
  for_each(allpt(nodes), [](const node &z) { cout << z.ans << rt; });

  return 0;
}


Fixed submission:
#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using VI = vector<int>;
using VL = vector<ll>;
using VVI = vector<vector<int>>;
using VVL = vector<vector<ll>>;
using PII = std::pair<int, int>;
using PLL = std::pair<ll, ll>;

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n)-1; i >= 0; i--)
#define rep2(i, s, n) for (int i = (s); i < (int)(n); i++)
#define rep3(i, s, n, d) for (int i = (s); i < (int)(n); i += (d))
#define allpt(v) (v).begin(), (v).end()
#define allpt_c(v) (v).cbegin(), (v).cend()
#define allpt_r(v) (v).rbegin(), (v).rend()

const int mod = 1e9 + 7;

const string wsp = " ";
const string tb = "\t";
const string rt = "\n";

template <typename T> void show1dvec(const vector<T> &v) {
  if (v.size() == 0)
    return;
  int n = v.size() - 1;
  rep(i, n) cout << v[i] << wsp;
  cout << v[n];
  return;
}

template <typename T> void show2dvec(const vector<vector<T>> &v) {
  int n = v.size();
  rep(i, n) show1dvec(v[i]);
}

template <typename T, typename S> void show1dpair(const vector<pair<T, S>> &v) {
  int n = v.size();
  rep(i, n) cout << v[i].first << wsp << v[i].second << rt;
  return;
}

template <typename T, typename S>
void pairzip(const vector<pair<T, S>> &v, vector<T> &t, vector<T> &s) {
  int n = v.size();
  rep(i, n) {
    t.push_back(v[i].first);
    s.push_back(v[i].second);
  }
  return;
}

template <typename T> void maxvec(vector<T> &v) {
  T s = v[0];
  int n = v.size();
  rep(i, n - 1) {
    if (s > v[i + 1]) {
      v[i + 1] = s;
    }
    s = v[i + 1];
  }
}

template <typename T, typename S> bool myfind(T t, S s) {
  return find(t.cbegin(), t.cend(), s) != t.cend();
}

bool check(int y, int x, int h, int w) {
  return 0 <= y && y < h && 0 <= x && x < w;
}

VI cumsum(VI &v) {
  int s = 0;
  VI ret = {0};

  rep(i, v.size()) {
    s += v[i];
    ret.push_back(s);
  }
  return ret;
}

void shuffle(VI &v, int t) {
  int temp = v[t - 1];
  rep(i, t - 1) v[t - 1 - i] = v[t - 2 - i];
  v[0] = temp;
}

struct node {
  VI children;
  ll ans = 1;
  ll ans_from_subtree = 1;
  ll ans_from_surtree = 1;
  int parent = -1;
  int subtree_size = 1;
  int surtree_size = 1;
};

void printsubtree(node n) {
  cout << "parent = " << n.parent << rt;
  cout << "children = ";
  show1dvec(n.children);
  cout << rt;
  cout << "subtree_size = " << n.subtree_size << rt;
  cout << "surtree_size = " << n.surtree_size << rt;
  cout << "ans_from_subtree = " << n.ans_from_subtree << rt;
  cout << "ans_from_surtree = " << n.ans_from_surtree << rt;
  cout << "ans = " << n.ans << rt;
  cout << rt;
}

ll pow_mod(int p, int q, int mod) {
  ll ret = 1, r = p;
  while (q) {
    if (q % 2)
      ret *= r, ret %= mod;
    r = (r * r) % mod, q /= 2;
  }
  return ret % mod;
}

ll const nmax = 200001;
VL frac_table(nmax, 1);
VL frac_inv_table(nmax, 1);

void dfs(const int &x, const VVI &connect, vector<node> &nodes) {
  for (auto z : connect[x]) {
    if (z != nodes[x].parent) {
      nodes[z].parent = x;
      nodes[x].children.push_back(z);
      dfs(z, connect, nodes);
    }
  }
}

void dfs2(const int &x, const int &n, const VVI &connect, vector<node> &nodes) {
  for (auto &z : nodes[x].children) {
    dfs2(z, n, connect, nodes);
    nodes[x].subtree_size += nodes[z].subtree_size;

    nodes[x].ans_from_subtree *= frac_inv_table[nodes[z].subtree_size];
    nodes[x].ans_from_subtree %= mod;
    nodes[x].ans_from_subtree *= nodes[z].ans_from_subtree;
    nodes[x].ans_from_subtree %= mod;
  }
  nodes[x].surtree_size = n - nodes[x].subtree_size;
  nodes[x].ans_from_subtree *= frac_table[nodes[x].subtree_size - 1];
  nodes[x].ans_from_subtree %= mod;
}

void dfs3(const int &x, const int &n, VVI &connect, vector<node> &nodes) {
  nodes[x].ans = nodes[x].ans_from_subtree;
  if (nodes[x].parent != -1) {
    nodes[x].ans *= frac_table[n - 1];
    nodes[x].ans %= mod;
    nodes[x].ans *= frac_inv_table[nodes[x].surtree_size];
    nodes[x].ans %= mod;
    nodes[x].ans *= frac_inv_table[nodes[x].subtree_size - 1];
    nodes[x].ans %= mod;
    nodes[x].ans *= nodes[x].ans_from_surtree;
    nodes[x].ans %= mod;
  }
  for (auto z : nodes[x].children) {
    nodes[z].ans_from_surtree *= nodes[x].ans;
    nodes[z].ans_from_surtree *= frac_inv_table[n - 1];
    nodes[z].ans_from_surtree %= mod;
    nodes[z].ans_from_surtree *= frac_table[nodes[z].subtree_size];
    nodes[z].ans_from_surtree %= mod;
    nodes[z].ans_from_surtree *= frac_table[n - 1 - nodes[z].subtree_size];
    nodes[z].ans_from_surtree %= mod;
    nodes[z].ans_from_surtree *=
        pow_mod(nodes[z].ans_from_subtree, mod - 2, mod);
    nodes[z].ans_from_surtree %= mod;

    dfs3(z, n, connect, nodes);
  }
}

int main() {

#ifdef DEBUG
  cout << "DEBUG MODE" << endl;
  ifstream in("input.txt"); // for debug
  cin.rdbuf(in.rdbuf());    // for debug
#endif

  int s = 1, t = 1;
  rep2(i, 1, nmax) {
    frac_table[i] = (frac_table[i - 1] * i) % mod;
    frac_inv_table[i] =
        (frac_inv_table[i - 1] * pow_mod(i, mod - 2, mod)) % mod;
  }

  int n, a, b;
  cin >> n;
  VVI connect(n);
  vector<node> nodes(n);
  rep(i, n - 1) {
    cin >> a >> b;
    a--, b--;
    connect[a].push_back(b);
    connect[b].push_back(a);
  }

  dfs(0, connect, nodes);
  dfs2(0, n, connect, nodes);
  dfs3(0, n, connect, nodes);
  // for_each(allpt(nodes), printsubtree);
  for_each(allpt(nodes), [](const node &z) { cout << z.ans << rt; });

  return 0;
}