Problem p02728 (C++) — buggy submission, verdict: Runtime Error

/*input

*/
#include <bits/stdc++.h>
#define up(i, a, b) for (int(i) = (a); (i) <= (b); ++(i))
#define down(i, b, a) for (int(i) = (b); i >= (a); --i)
#define debug(x) cerr << (x) << '\\n';
#define bits(x, i) ((x >> i) & 1)
#define mid ((l + r) / 2)
#define pr pair<int, int>
#define long long long
using namespace std;
const int N = 200005;
const int mod = 1e9 + 7;
vector<int> G[N];
int children[N], pchildren[N];
long ans[N], dp[N], pDp[N];
long fact[N];
int n;
void init() {
  up(i, 1, n) dp[i] = children[i] = 1;
  fact[0] = 1;
  for (int i = 1; i <= n; ++i)
    fact[i] = (fact[i - 1] * i * 1LL) % mod;
}
long power(long x, long n) {
  long ans = 1;
  for (int i = 0; i < 31; ++i) {
    if (bits(n, i))
      ans = (ans * x) % mod;
    x = (x * x) % mod;
  }
  return ans;
}
long inv(long num, long den) { return (num * power(den, mod - 2)) % mod; }
long C(int k, int n) {
  int num = fact[n];
  int den = (fact[k] * fact[n - k]) % mod;
  return inv(num, den);
}
void precal(int u, int par) {
  for (auto v : G[u]) {
    if (v == par)
      continue;
    precal(v, u);
    children[u] += children[v];
  }
  int remaider = children[u] - 1;
  for (auto v : G[u]) {
    if (v == par)
      continue;
    // cout << children[v] << ' ' << remaider << '\\n';
    long cur = (1LL * dp[v] * C(children[v], remaider)) % mod;
    dp[u] = (dp[u] * cur) % mod;
    remaider -= children[v];
  }
}
void rollback(int u, int v) {
  pDp[u] = dp[u];
  pDp[v] = dp[v];
  pchildren[u] = children[u];
  pchildren[v] = children[v];
}
void dfs(int u, int par) {
  ans[u] = dp[u];
  for (auto v : G[u]) {
    if (v == par)
      continue;
    rollback(u, v);
    dp[u] = inv(dp[u], (dp[v] * C(children[v], children[u] - 1)) % mod);
    children[u] -= children[v];
    children[v] += children[u];
    long mul = (dp[u] * C(children[u], children[v] - 1)) % mod;
    dp[v] = (dp[v] * mul) % mod;
    dfs(v, u);
    dp[u] = pDp[u];
    dp[v] = pDp[v];
    children[u] = pchildren[u];
    children[v] = pchildren[v];
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  up(i, 1, n - 1) {
    int u, v;
    cin >> u >> v;
    G[u].push_back(v);
    G[v].push_back(u);
  }
  init();
  precal(1, 0);
  // solve
  dfs(1, 0);
  for (int i = 1; i <= n; ++i)
    cout << ans[i] << '\\n';
}

Error: 0

Fixed submission:

/*input

*/
#include <bits/stdc++.h>
#define up(i, a, b) for (int(i) = (a); (i) <= (b); ++(i))
#define down(i, b, a) for (int(i) = (b); i >= (a); --i)
#define debug(x) cerr << (x) << '\\n';
#define bits(x, i) ((x >> i) & 1)
#define mid ((l + r) / 2)
#define pr pair<int, int>
#define long long long
using namespace std;
const int N = 100005;
const int mod = 1e9 + 7;
vector<int> G[N];
int children[N], pchildren[N];
long ans[N], dp[N], pDp[N];
long fact[N];
int n;
void init() {
  up(i, 1, n) dp[i] = children[i] = 1;
  fact[0] = 1;
  for (int i = 1; i <= n; ++i)
    fact[i] = (fact[i - 1] * i * 1LL) % mod;
}
long power(long x, long n) {
  long ans = 1;
  for (int i = 0; i < 31; ++i) {
    if (bits(n, i))
      ans = (ans * x) % mod;
    x = (x * x) % mod;
  }
  return ans;
}
long inv(long num, long den) { return (num * power(den, mod - 2)) % mod; }
long C(int k, int n) {
  int num = fact[n];
  int den = (fact[k] * fact[n - k]) % mod;
  return inv(num, den);
}
void precal(int u, int par) {
  for (auto v : G[u]) {
    if (v == par)
      continue;
    precal(v, u);
    children[u] += children[v];
  }
  int remaider = children[u] - 1;
  for (auto v : G[u]) {
    if (v == par)
      continue;
    // cout << children[v] << ' ' << remaider << '\\n';
    long cur = (1LL * dp[v] * C(children[v], remaider)) % mod;
    dp[u] = (dp[u] * cur) % mod;
    remaider -= children[v];
  }
}
void rollback(int u, int v) {
  pDp[u] = dp[u];
  pDp[v] = dp[v];
  pchildren[u] = children[u];
  pchildren[v] = children[v];
}
void dfs(int u, int par) {
  ans[u] = dp[u];
  for (auto v : G[u]) {
    if (v == par)
      continue;
    rollback(u, v);
    dp[u] = inv(dp[u], (dp[v] * C(children[v], children[u] - 1)) % mod);
    children[u] -= children[v];
    children[v] += children[u];
    long mul = (dp[u] * C(children[u], children[v] - 1)) % mod;
    dp[v] = (dp[v] * mul) % mod;
    dfs(v, u);
    dp[u] = pDp[u];
    dp[v] = pDp[v];
    children[u] = pchildren[u];
    children[v] = pchildren[v];
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  up(i, 1, n - 1) {
    int u, v;
    cin >> u >> v;
    G[u].push_back(v);
    G[v].push_back(u);
  }
  init();
  precal(1, 0);
  // solve
  dfs(1, 0);
  for (int i = 1; i <= n; ++i)
    cout << ans[i] << '\\n';
}