Problem p02965 (C++)

Buggy submission (status: Runtime Error):
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
#define SZ(x) ((int)((x).size()))

template <typename T1, typename T2>
string print_iterable(T1 begin_iter, T2 end_iter, int counter) {
  bool done_something = false;
  stringstream res;
  res << "[";
  for (; begin_iter != end_iter and counter; ++begin_iter) {
    done_something = true;
    counter--;
    res << *begin_iter << ", ";
  }
  string str = res.str();
  if (done_something) {
    str.pop_back();
    str.pop_back();
  }
  str += "]";
  return str;
}

vector<int> SortIndex(int size, std::function<bool(int, int)> compare) {
  vector<int> ord(size);
  for (int i = 0; i < size; i++)
    ord[i] = i;
  sort(ord.begin(), ord.end(), compare);
  return ord;
}

template <typename T> bool MinPlace(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <typename T> bool MaxPlace(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

template <typename S, typename T>
ostream &operator<<(ostream &out, const pair<S, T> &p) {
  out << "{" << p.first << ", " << p.second << "}";
  return out;
}

template <typename T> ostream &operator<<(ostream &out, const vector<T> &v) {
  out << "[";
  for (int i = 0; i < (int)v.size(); i++) {
    out << v[i];
    if (i != (int)v.size() - 1)
      out << ", ";
  }
  out << "]";
  return out;
}

template <class TH> void _dbg(const char *name, TH val) {
  clog << name << ": " << val << endl;
}
template <class TH, class... TA>
void _dbg(const char *names, TH curr_val, TA... vals) {
  while (*names != ',')
    clog << *names++;
  clog << ": " << curr_val << ", ";
  _dbg(names + 1, vals...);
}

#if DEBUG && !ONLINE_JUDGE
ifstream input_from_file("input.txt");
#define cin input_from_file

#define dbg(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#define dbg_arr(x, len)                                                        \
  clog << #x << ": " << print_iterable(x, x + len, -1) << endl;
#else
#define dbg(...)
#define dbg_arr(x, len)
#endif

///////////////////////////////////////////////////////////////////////////
//////////////////// DO NOT TOUCH BEFORE THIS LINE ////////////////////////
///////////////////////////////////////////////////////////////////////////

LL Inverse(LL n, LL m) {
  n %= m;
  if (n <= 1)
    return n; // Handles properly (n = 0, m = 1).
  return m - ((m * Inverse(m, n) - 1) / n);
}

const LL mod = 998244353;
const int MAXN = 4e6;
LL fact[MAXN];

LL binom(LL a, LL b) {
  assert(MAXN > a and a >= b and b >= 0);
  return fact[a] * Inverse(fact[b] * fact[a - b] % mod, mod) % mod;
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0); // Remove in problems with online queries!

  fact[0] = 1;
  for (int i = 1; i < MAXN; i++) {
    fact[i] = i * fact[i - 1] % mod;
    // invfact[i] = Inverse(fact[i], mod);
  }

  int N, M;
  cin >> N >> M;

  LL ans = N * binom(M + N - 2, N - 2) % mod;
  for (int k = 0; k <= M; k++) {
    LL q = 3 * M - k;
    if (q % 2)
      continue;
    q /= 2;
    LL ris = binom(q + N - 1, N - 1) - N * binom(q - M + N - 1, N - 1);
    ris %= mod;
    ris = ris * binom(N, k) % mod;
    ans += ris;
    ans %= mod;
  }
  if (ans < 0)
    ans += mod;
  cout << ans << "\n";
}


Fixed submission:
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
#define SZ(x) ((int)((x).size()))

template <typename T1, typename T2>
string print_iterable(T1 begin_iter, T2 end_iter, int counter) {
  bool done_something = false;
  stringstream res;
  res << "[";
  for (; begin_iter != end_iter and counter; ++begin_iter) {
    done_something = true;
    counter--;
    res << *begin_iter << ", ";
  }
  string str = res.str();
  if (done_something) {
    str.pop_back();
    str.pop_back();
  }
  str += "]";
  return str;
}

vector<int> SortIndex(int size, std::function<bool(int, int)> compare) {
  vector<int> ord(size);
  for (int i = 0; i < size; i++)
    ord[i] = i;
  sort(ord.begin(), ord.end(), compare);
  return ord;
}

template <typename T> bool MinPlace(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

template <typename T> bool MaxPlace(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

template <typename S, typename T>
ostream &operator<<(ostream &out, const pair<S, T> &p) {
  out << "{" << p.first << ", " << p.second << "}";
  return out;
}

template <typename T> ostream &operator<<(ostream &out, const vector<T> &v) {
  out << "[";
  for (int i = 0; i < (int)v.size(); i++) {
    out << v[i];
    if (i != (int)v.size() - 1)
      out << ", ";
  }
  out << "]";
  return out;
}

template <class TH> void _dbg(const char *name, TH val) {
  clog << name << ": " << val << endl;
}
template <class TH, class... TA>
void _dbg(const char *names, TH curr_val, TA... vals) {
  while (*names != ',')
    clog << *names++;
  clog << ": " << curr_val << ", ";
  _dbg(names + 1, vals...);
}

#if DEBUG && !ONLINE_JUDGE
ifstream input_from_file("input.txt");
#define cin input_from_file

#define dbg(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#define dbg_arr(x, len)                                                        \
  clog << #x << ": " << print_iterable(x, x + len, -1) << endl;
#else
#define dbg(...)
#define dbg_arr(x, len)
#endif

///////////////////////////////////////////////////////////////////////////
//////////////////// DO NOT TOUCH BEFORE THIS LINE ////////////////////////
///////////////////////////////////////////////////////////////////////////

LL Inverse(LL n, LL m) {
  n %= m;
  if (n <= 1)
    return n; // Handles properly (n = 0, m = 1).
  return m - ((m * Inverse(m, n) - 1) / n);
}

const LL mod = 998244353;
const int MAXN = 4e6;
LL fact[MAXN];

LL binom(LL a, LL b) {
  assert(MAXN > a and a >= b and b >= 0);
  return fact[a] * Inverse(fact[b] * fact[a - b] % mod, mod) % mod;
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0); // Remove in problems with online queries!

  fact[0] = 1;
  for (int i = 1; i < MAXN; i++) {
    fact[i] = i * fact[i - 1] % mod;
    // invfact[i] = Inverse(fact[i], mod);
  }

  int N, M;
  cin >> N >> M;

  LL ans = N * binom(M + N - 2, N - 2) % mod;
  for (int k = 0; k <= min(N, M); k++) {
    LL q = 3 * M - k;
    if (q % 2)
      continue;
    q /= 2;
    LL ris = binom(q + N - 1, N - 1) - N * binom(q - M + N - 1, N - 1);
    ris %= mod;
    ris = ris * binom(N, k) % mod;
    ans += ris;
    ans %= mod;
  }
  if (ans < 0)
    ans += mod;
  cout << ans << "\n";
}