Problem p03332 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> P;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;
#define pb push_back
#define mp make_pair
#define eps 1e-9
#define INF 2000000000
#define sz(x) ((int)(x).size())
#define fi first
#define sec second
#define all(x) (x).begin(), (x).end()
#define sq(x) ((x) * (x))
#define rep(i, n) for (int(i) = 0; (i) < (int)(n); (i)++)
#define repn(i, a, n) for (int(i) = (a); (i) < (int)(n); (i)++)
#define EQ(a, b) (abs((a) - (b)) < eps)
template <class T> void chmin(T &a, const T &b) {
  if (a > b)
    a = b;
}
template <class T> void chmax(T &a, const T &b) {
  if (a < b)
    a = b;
}
#define MOD 998244353ll // prime
// How to devide :
// ModInt a(6ll);
// ModInt b(2ll);
// a *= b.exp(MOD-2ll);  -> a/=b;  result: a = 3
struct ModInt {
  ll val;
  ModInt() : val(0ll) {}
  ModInt(ll v) : val(((v % MOD) + MOD) % MOD) {}
  ModInt exp(ll y) const {
    if (!y)
      return ModInt(1ll);
    ModInt a = exp(y / 2ll);
    a *= a;
    if (y & 1)
      a *= (*this);
    return a;
  }
  bool operator==(const ModInt &x) const { return val == x.val; }
  inline bool operator!=(const ModInt &x) const { return !(*this == x); }
  bool operator<(const ModInt &x) const { return val < x.val; }
  bool operator>(const ModInt &x) const { return val > x.val; }
  inline bool operator>=(const ModInt &x) const { return !(*this < x); }
  inline bool operator<=(const ModInt &x) const { return !(*this > x); }
  ModInt &operator+=(const ModInt &x) {
    if ((val += x.val) >= MOD)
      val -= MOD;
    return *this;
  }
  ModInt &operator-=(const ModInt &x) {
    if ((val += MOD - x.val) >= MOD)
      val -= MOD;
    return *this;
  }
  ModInt &operator*=(const ModInt &x) {
    (val *= x.val) %= MOD;
    return *this;
  }
  ModInt operator+(const ModInt &x) const { return ModInt(*this) += x; }
  ModInt operator-(const ModInt &x) const { return ModInt(*this) -= x; }
  ModInt operator*(const ModInt &x) const { return ModInt(*this) *= x; }
};
istream &operator>>(istream &i, ModInt &x) {
  i >> x.val;
  return i;
}
ostream &operator<<(ostream &o, const ModInt &x) {
  o << x.val;
  return o;
}
ModInt pow(ModInt a, ll x) {
  ModInt res = ModInt(1ll);
  while (x) {
    if (x & 1)
      res *= a;
    x >>= 1;
    a = a * a;
  }
  return res;
}
const int SIZE = 100100;
ModInt inv[SIZE + 10], fac[SIZE + 10], facinv[SIZE + 10];
// notice: 0C0 = 1
ModInt nCr(int n, int r) {
  assert(!(n < r));
  assert(!(n < 0 || r < 0));
  return fac[n] * facinv[r] * facinv[n - r];
}
void init() {
  fac[0] = ModInt(1ll);
  for (int i = 1; i <= SIZE; i++)
    fac[i] = fac[i - 1] * ModInt(i);
  inv[1] = ModInt(1ll);
  for (int i = 2; i <= SIZE; i++)
    inv[i] = ModInt(0ll) - ModInt(MOD / i) * inv[MOD % i];
  facinv[0] = ModInt(1ll);
  for (int i = 1; i <= SIZE; i++)
    facinv[i] = facinv[i - 1] * inv[i];
  return;
}
int N;
ll A, B, K;
int main() {
  init();
  cin >> N >> A >> B >> K;
  ModInt ans;
  for (int i = 0; i <= N; i++) {
    ll rem = K - A * (ll)i;
    if (rem < 0ll)
      break;
    if (rem % B != 0ll)
      continue;
    ll p = (ll)i, q = rem / B;
    if (q > N)
      continue;
    ans += nCr(N, p) * nCr(N, q);
  }
  cout << ans << endl;
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> P;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;
#define pb push_back
#define mp make_pair
#define eps 1e-9
#define INF 2000000000
#define sz(x) ((int)(x).size())
#define fi first
#define sec second
#define all(x) (x).begin(), (x).end()
#define sq(x) ((x) * (x))
#define rep(i, n) for (int(i) = 0; (i) < (int)(n); (i)++)
#define repn(i, a, n) for (int(i) = (a); (i) < (int)(n); (i)++)
#define EQ(a, b) (abs((a) - (b)) < eps)
template <class T> void chmin(T &a, const T &b) {
  if (a > b)
    a = b;
}
template <class T> void chmax(T &a, const T &b) {
  if (a < b)
    a = b;
}
#define MOD 998244353ll // prime
// How to devide :
// ModInt a(6ll);
// ModInt b(2ll);
// a *= b.exp(MOD-2ll);  -> a/=b;  result: a = 3
struct ModInt {
  ll val;
  ModInt() : val(0ll) {}
  ModInt(ll v) : val(((v % MOD) + MOD) % MOD) {}
  ModInt exp(ll y) const {
    if (!y)
      return ModInt(1ll);
    ModInt a = exp(y / 2ll);
    a *= a;
    if (y & 1)
      a *= (*this);
    return a;
  }
  bool operator==(const ModInt &x) const { return val == x.val; }
  inline bool operator!=(const ModInt &x) const { return !(*this == x); }
  bool operator<(const ModInt &x) const { return val < x.val; }
  bool operator>(const ModInt &x) const { return val > x.val; }
  inline bool operator>=(const ModInt &x) const { return !(*this < x); }
  inline bool operator<=(const ModInt &x) const { return !(*this > x); }
  ModInt &operator+=(const ModInt &x) {
    if ((val += x.val) >= MOD)
      val -= MOD;
    return *this;
  }
  ModInt &operator-=(const ModInt &x) {
    if ((val += MOD - x.val) >= MOD)
      val -= MOD;
    return *this;
  }
  ModInt &operator*=(const ModInt &x) {
    (val *= x.val) %= MOD;
    return *this;
  }
  ModInt operator+(const ModInt &x) const { return ModInt(*this) += x; }
  ModInt operator-(const ModInt &x) const { return ModInt(*this) -= x; }
  ModInt operator*(const ModInt &x) const { return ModInt(*this) *= x; }
};
istream &operator>>(istream &i, ModInt &x) {
  i >> x.val;
  return i;
}
ostream &operator<<(ostream &o, const ModInt &x) {
  o << x.val;
  return o;
}
ModInt pow(ModInt a, ll x) {
  ModInt res = ModInt(1ll);
  while (x) {
    if (x & 1)
      res *= a;
    x >>= 1;
    a = a * a;
  }
  return res;
}
const int SIZE = 1001000;
ModInt inv[SIZE + 10], fac[SIZE + 10], facinv[SIZE + 10];
// notice: 0C0 = 1
ModInt nCr(int n, int r) {
  assert(!(n < r));
  assert(!(n < 0 || r < 0));
  return fac[n] * facinv[r] * facinv[n - r];
}
void init() {
  fac[0] = ModInt(1ll);
  for (int i = 1; i <= SIZE; i++)
    fac[i] = fac[i - 1] * ModInt(i);
  inv[1] = ModInt(1ll);
  for (int i = 2; i <= SIZE; i++)
    inv[i] = ModInt(0ll) - ModInt(MOD / i) * inv[MOD % i];
  facinv[0] = ModInt(1ll);
  for (int i = 1; i <= SIZE; i++)
    facinv[i] = facinv[i - 1] * inv[i];
  return;
}
int N;
ll A, B, K;
int main() {
  init();
  cin >> N >> A >> B >> K;
  ModInt ans;
  for (int i = 0; i <= N; i++) {
    ll rem = K - A * (ll)i;
    if (rem < 0ll)
      break;
    if (rem % B != 0ll)
      continue;
    ll p = (ll)i, q = rem / B;
    if (q > N)
      continue;
    ans += nCr(N, p) * nCr(N, q);
  }
  cout << ans << endl;
  return 0;
}