Problem p03332 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <cassert>
#include <chrono>
#include <cmath>
#include <cstdio>
#include <ctime>
#include <functional>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
using namespace std;

namespace {
using Integer = long long; //__int128;
template <class T, class S> istream &operator>>(istream &is, pair<T, S> &p) {
  return is >> p.first >> p.second;
}
template <class T> istream &operator>>(istream &is, vector<T> &vec) {
  for (T &val : vec)
    is >> val;
  return is;
}
template <class T> istream &operator,(istream &is, T &val) { return is >> val; }
template <class T, class S>
ostream &operator<<(ostream &os, const pair<T, S> &p) {
  return os << p.first << " " << p.second;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  for (size_t i = 0; i < vec.size(); i++)
    os << vec[i] << (i == vec.size() - 1 ? "" : " ");
  return os;
}
template <class T> ostream &operator,(ostream &os, const T &val) {
  return os << " " << val;
}

template <class H> void print(const H &head) { cout << head; }
template <class H, class... T> void print(const H &head, const T &...tail) {
  cout << head << " ";
  print(tail...);
}
template <class... T> void println(const T &...values) {
  print(values...);
  cout << endl;
}

template <class H> void eprint(const H &head) { cerr << head; }
template <class H, class... T> void eprint(const H &head, const T &...tail) {
  cerr << head << " ";
  eprint(tail...);
}
template <class... T> void eprintln(const T &...values) {
  eprint(values...);
  cerr << endl;
}

class range {
  Integer start_, end_, step_;

public:
  struct range_iterator {
    Integer val, step_;
    range_iterator(Integer v, Integer step) : val(v), step_(step) {}
    Integer operator*() { return val; }
    void operator++() { val += step_; }
    bool operator!=(range_iterator &x) {
      return step_ > 0 ? val < x.val : val > x.val;
    }
  };
  range(Integer len) : start_(0), end_(len), step_(1) {}
  range(Integer start, Integer end) : start_(start), end_(end), step_(1) {}
  range(Integer start, Integer end, Integer step)
      : start_(start), end_(end), step_(step) {}
  range_iterator begin() { return range_iterator(start_, step_); }
  range_iterator end() { return range_iterator(end_, step_); }
};

inline string operator"" _s(const char *str, size_t size) {
  return move(string(str));
}
constexpr Integer my_pow(Integer x, Integer k, Integer z = 1) {
  return k == 0    ? z
         : k == 1  ? z * x
         : (k & 1) ? my_pow(x * x, k >> 1, z * x)
                   : my_pow(x * x, k >> 1, z);
}
constexpr Integer my_pow_mod(Integer x, Integer k, Integer M, Integer z = 1) {
  return k == 0    ? z % M
         : k == 1  ? z * x % M
         : (k & 1) ? my_pow_mod(x * x % M, k >> 1, M, z * x % M)
                   : my_pow_mod(x * x % M, k >> 1, M, z);
}
constexpr unsigned long long operator"" _ten(unsigned long long value) {
  return my_pow(10, value);
}

inline int k_bit(Integer x, int k) { return (x >> k) & 1; } // 0-indexed

mt19937 mt(chrono::duration_cast<chrono::nanoseconds>(
               chrono::steady_clock::now().time_since_epoch())
               .count());

template <class T> string join(const vector<T> &v, const string &sep) {
  stringstream ss;
  for (size_t i = 0; i < v.size(); i++) {
    if (i > 0)
      ss << sep;
    ss << v[i];
  }
  return ss.str();
}

inline string operator*(string s, int k) {
  string ret;
  while (k) {
    if (k & 1)
      ret += s;
    s += s;
    k >>= 1;
  }
  return ret;
}
} // namespace
constexpr long long mod = 998244353;

class combination_mod {
  const long long mod;
  const long long size;

  vector<long long> fact;     // n!
  vector<long long> fact_inv; // (n!)^-1

  void make_fact() {
    fact[0] = 1;
    for (long long i = 1; i < size; i++) {
      fact[i] = fact[i - 1] * i % mod;
    }
  }

  void make_fact_inv() {
    fact_inv[0] = fact_inv[1] = 1;
    for (long long i = 2; i < size; i++) {
      fact_inv[i] = fact_inv[mod % i] * (mod - mod / i) % mod; // x ^ -1
    }
    for (int i = 2; i < size; i++) {
      fact_inv[i] = fact_inv[i - 1] * fact_inv[i] % mod; // x! ^ -1
    }
  }

public:
  combination_mod(long long mod_, long long size_ = 2000000)
      : mod(mod_), size(size_ + 1) {
    fact.resize(size);
    fact_inv.resize(size);
    make_fact();
    make_fact_inv();
  }

  // nCk mod p O(1)
  long long operator()(long long n, long long k) {
    if (k == 0 || n == k)
      return 1;
    long long ret = fact[n] * fact_inv[k] % mod * fact_inv[n - k] % mod;
    return ret;
  }
};

int main() {
  long long n, a, b, k;
  cin >> n, a, b, k;

  combination_mod c(mod, 1000000);

  long long ans = 0;
  for (long long x = 0; x <= n; x++) {
    long long y = k - x * a;
    if (y % b != 0)
      continue;
    y /= b;
    if (y > n)
      continue;
    ans += c(n, x) * c(n, y) % mod;
    ans %= mod;
  }

  println(ans % mod);

  return 0;
}


Fixed submission:
#include <algorithm>
#include <cassert>
#include <chrono>
#include <cmath>
#include <cstdio>
#include <ctime>
#include <functional>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
using namespace std;

namespace {
using Integer = long long; //__int128;
template <class T, class S> istream &operator>>(istream &is, pair<T, S> &p) {
  return is >> p.first >> p.second;
}
template <class T> istream &operator>>(istream &is, vector<T> &vec) {
  for (T &val : vec)
    is >> val;
  return is;
}
template <class T> istream &operator,(istream &is, T &val) { return is >> val; }
template <class T, class S>
ostream &operator<<(ostream &os, const pair<T, S> &p) {
  return os << p.first << " " << p.second;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  for (size_t i = 0; i < vec.size(); i++)
    os << vec[i] << (i == vec.size() - 1 ? "" : " ");
  return os;
}
template <class T> ostream &operator,(ostream &os, const T &val) {
  return os << " " << val;
}

template <class H> void print(const H &head) { cout << head; }
template <class H, class... T> void print(const H &head, const T &...tail) {
  cout << head << " ";
  print(tail...);
}
template <class... T> void println(const T &...values) {
  print(values...);
  cout << endl;
}

template <class H> void eprint(const H &head) { cerr << head; }
template <class H, class... T> void eprint(const H &head, const T &...tail) {
  cerr << head << " ";
  eprint(tail...);
}
template <class... T> void eprintln(const T &...values) {
  eprint(values...);
  cerr << endl;
}

class range {
  Integer start_, end_, step_;

public:
  struct range_iterator {
    Integer val, step_;
    range_iterator(Integer v, Integer step) : val(v), step_(step) {}
    Integer operator*() { return val; }
    void operator++() { val += step_; }
    bool operator!=(range_iterator &x) {
      return step_ > 0 ? val < x.val : val > x.val;
    }
  };
  range(Integer len) : start_(0), end_(len), step_(1) {}
  range(Integer start, Integer end) : start_(start), end_(end), step_(1) {}
  range(Integer start, Integer end, Integer step)
      : start_(start), end_(end), step_(step) {}
  range_iterator begin() { return range_iterator(start_, step_); }
  range_iterator end() { return range_iterator(end_, step_); }
};

inline string operator"" _s(const char *str, size_t size) {
  return move(string(str));
}
constexpr Integer my_pow(Integer x, Integer k, Integer z = 1) {
  return k == 0    ? z
         : k == 1  ? z * x
         : (k & 1) ? my_pow(x * x, k >> 1, z * x)
                   : my_pow(x * x, k >> 1, z);
}
constexpr Integer my_pow_mod(Integer x, Integer k, Integer M, Integer z = 1) {
  return k == 0    ? z % M
         : k == 1  ? z * x % M
         : (k & 1) ? my_pow_mod(x * x % M, k >> 1, M, z * x % M)
                   : my_pow_mod(x * x % M, k >> 1, M, z);
}
constexpr unsigned long long operator"" _ten(unsigned long long value) {
  return my_pow(10, value);
}

inline int k_bit(Integer x, int k) { return (x >> k) & 1; } // 0-indexed

mt19937 mt(chrono::duration_cast<chrono::nanoseconds>(
               chrono::steady_clock::now().time_since_epoch())
               .count());

template <class T> string join(const vector<T> &v, const string &sep) {
  stringstream ss;
  for (size_t i = 0; i < v.size(); i++) {
    if (i > 0)
      ss << sep;
    ss << v[i];
  }
  return ss.str();
}

inline string operator*(string s, int k) {
  string ret;
  while (k) {
    if (k & 1)
      ret += s;
    s += s;
    k >>= 1;
  }
  return ret;
}
} // namespace
constexpr long long mod = 998244353;

class combination_mod {
  const long long mod;
  const long long size;

  vector<long long> fact;     // n!
  vector<long long> fact_inv; // (n!)^-1

  void make_fact() {
    fact[0] = 1;
    for (long long i = 1; i < size; i++) {
      fact[i] = fact[i - 1] * i % mod;
    }
  }

  void make_fact_inv() {
    fact_inv[0] = fact_inv[1] = 1;
    for (long long i = 2; i < size; i++) {
      fact_inv[i] = fact_inv[mod % i] * (mod - mod / i) % mod; // x ^ -1
    }
    for (int i = 2; i < size; i++) {
      fact_inv[i] = fact_inv[i - 1] * fact_inv[i] % mod; // x! ^ -1
    }
  }

public:
  combination_mod(long long mod_, long long size_ = 2000000)
      : mod(mod_), size(size_ + 1) {
    fact.resize(size);
    fact_inv.resize(size);
    make_fact();
    make_fact_inv();
  }

  // nCk mod p O(1)
  long long operator()(long long n, long long k) {
    if (k == 0 || n == k)
      return 1;
    long long ret = fact[n] * fact_inv[k] % mod * fact_inv[n - k] % mod;
    return ret;
  }
};

int main() {
  long long n, a, b, k;
  cin >> n, a, b, k;

  combination_mod c(mod, 1000000);

  long long ans = 0;
  for (long long x = 0; x <= n; x++) {
    long long y = k - x * a;
    if (y < 0)
      continue;
    if (y % b != 0)
      continue;
    y /= b;
    if (y > n)
      continue;
    ans += c(n, x) * c(n, y) % mod;
    ans %= mod;
  }

  println(ans % mod);

  return 0;
}