Problem p02539 (C++)

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

const int N = 1 << 18;
const int mod = 998244353;
const int root = 3;
int lim, rev[N], w[N], wn[N], inv_lim;
void reduce(int &x) { x = (x + mod) % mod; }
int POW(int x, int y, int ans = 1) {
  for (; y; y >>= 1, x = (long long)x * x % mod)
    if (y & 1)
      ans = (long long)ans * x % mod;
  return ans;
}
void precompute(int len) {
  lim = wn[0] = 1;
  int s = -1;
  while (lim < len)
    lim <<= 1, ++s;
  for (int i = 0; i < lim; ++i)
    rev[i] = rev[i >> 1] >> 1 | (i & 1) << s;
  const int g = POW(root, (mod - 1) / lim);
  inv_lim = POW(lim, mod - 2);
  for (int i = 1; i < lim; ++i)
    wn[i] = (long long)wn[i - 1] * g % mod;
}
void ntt(vector<int> &a, int typ) {
  for (int i = 0; i < lim; ++i)
    if (i < rev[i])
      swap(a[i], a[rev[i]]);
  for (int i = 1; i < lim; i <<= 1) {
    for (int j = 0, t = lim / i / 2; j < i; ++j)
      w[j] = wn[j * t];
    for (int j = 0; j < lim; j += i << 1)
      for (int k = 0; k < i; ++k) {
        const int x = a[k + j], y = (long long)a[k + j + i] * w[k] % mod;
        reduce(a[k + j] += y - mod), reduce(a[k + j + i] = x - y);
      }
  }
  if (!typ) {
    reverse(a.begin() + 1, a.begin() + lim);
    for (int i = 0; i < lim; ++i)
      a[i] = (long long)a[i] * inv_lim % mod;
  }
}
vector<int> multiply(vector<int> f, vector<int> g) {
  int n = (int)f.size() + (int)g.size() - 1;
  precompute(n);
  vector<int> a = f, b = g;
  a.resize(lim);
  b.resize(lim);
  ntt(a, 1), ntt(b, 1);
  for (int i = 0; i < lim; ++i)
    a[i] = (long long)a[i] * b[i] % mod;
  ntt(a, 0);
  // while((int)a.size() && a.back() == 0) a.pop_back();
  return a;
}

template <const int32_t MOD> struct modint {
  int32_t value;
  modint() = default;
  modint(int32_t value_) : value(value_) {}
  inline modint<MOD> operator+(modint<MOD> other) const {
    int32_t c = this->value + other.value;
    return modint<MOD>(c >= MOD ? c - MOD : c);
  }
  inline modint<MOD> operator-(modint<MOD> other) const {
    int32_t c = this->value - other.value;
    return modint<MOD>(c < 0 ? c + MOD : c);
  }
  inline modint<MOD> operator*(modint<MOD> other) const {
    int32_t c = (int64_t)this->value * other.value % MOD;
    return modint<MOD>(c < 0 ? c + MOD : c);
  }
  inline modint<MOD> &operator+=(modint<MOD> other) {
    this->value += other.value;
    if (this->value >= MOD)
      this->value -= MOD;
    return *this;
  }
  inline modint<MOD> &operator-=(modint<MOD> other) {
    this->value -= other.value;
    if (this->value < 0)
      this->value += MOD;
    return *this;
  }
  inline modint<MOD> &operator*=(modint<MOD> other) {
    this->value = (int64_t)this->value * other.value % MOD;
    if (this->value < 0)
      this->value += MOD;
    return *this;
  }
  inline modint<MOD> operator-() const {
    return modint<MOD>(this->value ? MOD - this->value : 0);
  }
  modint<MOD> pow(uint64_t k) const {
    modint<MOD> x = *this, y = 1;
    for (; k; k >>= 1) {
      if (k & 1)
        y *= x;
      x *= x;
    }
    return y;
  }
  modint<MOD> inv() const { return pow(MOD - 2); } // MOD must be a prime
  inline modint<MOD> operator/(modint<MOD> other) const {
    return *this * other.inv();
  }
  inline modint<MOD> operator/=(modint<MOD> other) {
    return *this *= other.inv();
  }
  inline bool operator==(modint<MOD> other) const {
    return value == other.value;
  }
  inline bool operator!=(modint<MOD> other) const {
    return value != other.value;
  }
  inline bool operator<(modint<MOD> other) const { return value < other.value; }
  inline bool operator>(modint<MOD> other) const { return value > other.value; }
};
template <int32_t MOD> modint<MOD> operator*(int64_t value, modint<MOD> n) {
  return modint<MOD>(value) * n;
}
template <int32_t MOD> modint<MOD> operator*(int32_t value, modint<MOD> n) {
  return modint<MOD>(value % MOD) * n;
}
template <int32_t MOD> istream &operator>>(istream &in, modint<MOD> &n) {
  return in >> n.value;
}
template <int32_t MOD> ostream &operator<<(ostream &out, modint<MOD> n) {
  return out << n.value;
}

using mint = modint<mod>;

struct Combi {
  int n;
  vector<mint> facts, finvs, invs;
  Combi(int _n) : n(_n), facts(_n), finvs(_n), invs(_n) {
    facts[0] = finvs[0] = 1;
    invs[1] = 1;
    for (int i = 2; i < n; i++)
      invs[i] = invs[mod % i] * (-mod / i);
    for (int i = 1; i < n; i++) {
      facts[i] = facts[i - 1] * i;
      finvs[i] = finvs[i - 1] * invs[i];
    }
  }
  inline mint fact(int n) { return facts[n]; }
  inline mint finv(int n) { return finvs[n]; }
  inline mint inv(int n) { return invs[n]; }
  inline mint ncr(int n, int k) {
    return n < k ? 0 : facts[n] * finvs[k] * finvs[n - k];
  }
};
Combi C(N);

int a[N];
mint f[N];
vector<int> c[N];
vector<int> yo(int l, int r) {
  if (l == r)
    return c[l];
  int mid = l + r >> 1;
  return multiply(yo(l, mid), yo(mid + 1, r));
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin >> n;
  n *= 2;
  for (int i = 1; i <= n; i++) {
    int k;
    cin >> k;
    a[k]++;
  }
  f[0] = 1;
  for (int i = 2; i < N; i += 2) {
    f[i] = C.fact(i) / C.fact(i / 2) / mint(2).pow(i / 2);
  }
  for (int i = 1; i < N; i++) {
    c[i] = vector<int>(a[i] + 1, 0);
    c[i][0] = 1;
    for (int k = 2; k <= a[i]; k += 2) {
      c[i][k] = (C.ncr(a[i], k) * f[k]).value;
    }
  }
  auto cnt = yo(1, 100000);
  cnt.resize(n + 1);
  mint ans = 0;
  for (int i = 0; i <= n; i += 2) {
    mint sgn = (i / 2) & 1 ? mod - 1 : 1;
    ans += sgn * f[n - i] * cnt[i];
  }
  cout << ans << '\n';
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;

const int N = 1 << 18;
const int mod = 998244353;
const int root = 3;
int lim, rev[N], w[N], wn[N], inv_lim;
void reduce(int &x) { x = (x + mod) % mod; }
int POW(int x, int y, int ans = 1) {
  for (; y; y >>= 1, x = (long long)x * x % mod)
    if (y & 1)
      ans = (long long)ans * x % mod;
  return ans;
}
void precompute(int len) {
  lim = wn[0] = 1;
  int s = -1;
  while (lim < len)
    lim <<= 1, ++s;
  for (int i = 0; i < lim; ++i)
    rev[i] = rev[i >> 1] >> 1 | (i & 1) << s;
  const int g = POW(root, (mod - 1) / lim);
  inv_lim = POW(lim, mod - 2);
  for (int i = 1; i < lim; ++i)
    wn[i] = (long long)wn[i - 1] * g % mod;
}
void ntt(vector<int> &a, int typ) {
  for (int i = 0; i < lim; ++i)
    if (i < rev[i])
      swap(a[i], a[rev[i]]);
  for (int i = 1; i < lim; i <<= 1) {
    for (int j = 0, t = lim / i / 2; j < i; ++j)
      w[j] = wn[j * t];
    for (int j = 0; j < lim; j += i << 1)
      for (int k = 0; k < i; ++k) {
        const int x = a[k + j], y = (long long)a[k + j + i] * w[k] % mod;
        reduce(a[k + j] += y - mod), reduce(a[k + j + i] = x - y);
      }
  }
  if (!typ) {
    reverse(a.begin() + 1, a.begin() + lim);
    for (int i = 0; i < lim; ++i)
      a[i] = (long long)a[i] * inv_lim % mod;
  }
}
vector<int> multiply(vector<int> f, vector<int> g) {
  if (f.size() > 100000)
    f.resize(100001);
  if (g.size() > 100000)
    g.resize(100001);
  int n = (int)f.size() + (int)g.size() - 1;
  precompute(n);
  vector<int> a = f, b = g;
  a.resize(lim);
  b.resize(lim);
  ntt(a, 1), ntt(b, 1);
  for (int i = 0; i < lim; ++i)
    a[i] = (long long)a[i] * b[i] % mod;
  ntt(a, 0);
  // while((int)a.size() && a.back() == 0) a.pop_back();
  return a;
}

template <const int32_t MOD> struct modint {
  int32_t value;
  modint() = default;
  modint(int32_t value_) : value(value_) {}
  inline modint<MOD> operator+(modint<MOD> other) const {
    int32_t c = this->value + other.value;
    return modint<MOD>(c >= MOD ? c - MOD : c);
  }
  inline modint<MOD> operator-(modint<MOD> other) const {
    int32_t c = this->value - other.value;
    return modint<MOD>(c < 0 ? c + MOD : c);
  }
  inline modint<MOD> operator*(modint<MOD> other) const {
    int32_t c = (int64_t)this->value * other.value % MOD;
    return modint<MOD>(c < 0 ? c + MOD : c);
  }
  inline modint<MOD> &operator+=(modint<MOD> other) {
    this->value += other.value;
    if (this->value >= MOD)
      this->value -= MOD;
    return *this;
  }
  inline modint<MOD> &operator-=(modint<MOD> other) {
    this->value -= other.value;
    if (this->value < 0)
      this->value += MOD;
    return *this;
  }
  inline modint<MOD> &operator*=(modint<MOD> other) {
    this->value = (int64_t)this->value * other.value % MOD;
    if (this->value < 0)
      this->value += MOD;
    return *this;
  }
  inline modint<MOD> operator-() const {
    return modint<MOD>(this->value ? MOD - this->value : 0);
  }
  modint<MOD> pow(uint64_t k) const {
    modint<MOD> x = *this, y = 1;
    for (; k; k >>= 1) {
      if (k & 1)
        y *= x;
      x *= x;
    }
    return y;
  }
  modint<MOD> inv() const { return pow(MOD - 2); } // MOD must be a prime
  inline modint<MOD> operator/(modint<MOD> other) const {
    return *this * other.inv();
  }
  inline modint<MOD> operator/=(modint<MOD> other) {
    return *this *= other.inv();
  }
  inline bool operator==(modint<MOD> other) const {
    return value == other.value;
  }
  inline bool operator!=(modint<MOD> other) const {
    return value != other.value;
  }
  inline bool operator<(modint<MOD> other) const { return value < other.value; }
  inline bool operator>(modint<MOD> other) const { return value > other.value; }
};
template <int32_t MOD> modint<MOD> operator*(int64_t value, modint<MOD> n) {
  return modint<MOD>(value) * n;
}
template <int32_t MOD> modint<MOD> operator*(int32_t value, modint<MOD> n) {
  return modint<MOD>(value % MOD) * n;
}
template <int32_t MOD> istream &operator>>(istream &in, modint<MOD> &n) {
  return in >> n.value;
}
template <int32_t MOD> ostream &operator<<(ostream &out, modint<MOD> n) {
  return out << n.value;
}

using mint = modint<mod>;

struct Combi {
  int n;
  vector<mint> facts, finvs, invs;
  Combi(int _n) : n(_n), facts(_n), finvs(_n), invs(_n) {
    facts[0] = finvs[0] = 1;
    invs[1] = 1;
    for (int i = 2; i < n; i++)
      invs[i] = invs[mod % i] * (-mod / i);
    for (int i = 1; i < n; i++) {
      facts[i] = facts[i - 1] * i;
      finvs[i] = finvs[i - 1] * invs[i];
    }
  }
  inline mint fact(int n) { return facts[n]; }
  inline mint finv(int n) { return finvs[n]; }
  inline mint inv(int n) { return invs[n]; }
  inline mint ncr(int n, int k) {
    return n < k ? 0 : facts[n] * finvs[k] * finvs[n - k];
  }
};
Combi C(N);

int a[N];
mint f[N];
vector<int> c[N];
vector<int> yo(int l, int r) {
  if (l == r)
    return c[l];
  int mid = l + r >> 1;
  return multiply(yo(l, mid), yo(mid + 1, r));
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin >> n;
  n *= 2;
  for (int i = 1; i <= n; i++) {
    int k;
    cin >> k;
    a[k]++;
  }
  f[0] = 1;
  for (int i = 2; i < N; i += 2) {
    f[i] = C.fact(i) / C.fact(i / 2) / mint(2).pow(i / 2);
  }
  for (int i = 1; i < N; i++) {
    c[i] = vector<int>(a[i] + 1, 0);
    c[i][0] = 1;
    for (int k = 2; k <= a[i]; k += 2) {
      c[i][k] = (C.ncr(a[i], k) * f[k]).value;
    }
  }
  auto cnt = yo(1, 100000);
  cnt.resize(n + 1);
  mint ans = 0;
  for (int i = 0; i <= n; i += 2) {
    mint sgn = (i / 2) & 1 ? mod - 1 : 1;
    ans += sgn * f[n - i] * cnt[i];
  }
  cout << ans << '\n';
  return 0;
}