Problem p03332 (C++)

Buggy submission (status: Runtime Error):
#pragma GCC optimize("O3")
#include "bits/stdc++.h"

using namespace std;
using ll = long long int;

#define debug(v)                                                               \
  {                                                                            \
    printf("L%d %s > ", __LINE__, #v);                                         \
    cout << (v) << endl;                                                       \
  }
#define debugv(v)                                                              \
  {                                                                            \
    printf("L%d %s > ", __LINE__, #v);                                         \
    for (auto e : (v)) {                                                       \
      cout << e << " ";                                                        \
    }                                                                          \
    cout << endl;                                                              \
  }
#define debuga(m, w)                                                           \
  {                                                                            \
    printf("L%d %s > ", __LINE__, #m);                                         \
    for (int x = 0; x < (w); x++) {                                            \
      cout << (m)[x] << " ";                                                   \
    }                                                                          \
    cout << endl;                                                              \
  }
#define debugaa(m, h, w)                                                       \
  {                                                                            \
    printf("L%d %s >\n", __LINE__, #m);                                        \
    for (int y = 0; y < (h); y++) {                                            \
      for (int x = 0; x < (w); x++) {                                          \
        cout << (m)[y][x] << " ";                                              \
      }                                                                        \
      cout << endl;                                                            \
    }                                                                          \
  }
#define ALL(v) (v).begin(), (v).end()
#define repeat(cnt, l)                                                         \
  for (remove_const<decltype(l)>::type cnt = 0; (cnt) < (l); ++(cnt))
#define rrepeat(cnt, l) for (auto cnt = (l)-1; 0 <= (cnt); --(cnt))
#define iterate(cnt, b, e) for (auto cnt = (b); (cnt) != (e); ++(cnt))
#define diterate(cnt, b, e) for (auto cnt = (b); (cnt) != (e); --(cnt))
const ll MD = 998244353ll;
const long double PI = 3.1415926535897932384626433832795L;
inline void assert_call(bool assertion, function<void()> f) {
  if (!assertion) {
    cerr << "assertion fault:" << endl;
    f();
    abort();
  }
}
template <typename T1, typename T2>
inline ostream &operator<<(ostream &o, const pair<T1, T2> p) {
  o << '(' << p.first << ':' << p.second << ')';
  return o;
}
template <typename Vec>
inline ostream &_ostream_vecprint(ostream &o, const Vec &p) {
  o << '[';
  for (auto &e : p)
    o << e << ',';
  o << ']';
  return o;
}
template <typename T>
inline ostream &operator<<(ostream &o, const vector<T> &v) {
  return _ostream_vecprint(o, v);
}
template <typename T, size_t S>
inline ostream &operator<<(ostream &o, const array<T, S> &v) {
  return _ostream_vecprint(o, v);
}
template <typename T> inline T &maxset(T &to, const T &val) {
  return to = max(to, val);
}
template <typename T> inline T &minset(T &to, const T &val) {
  return to = min(to, val);
}
void bye(string s, int code = 0) {
  cout << s << endl;
  exit(code);
}
mt19937_64 randdev(8901016);
template <typename T> inline T rand(T l, T h) {
  return uniform_int_distribution<T>(l, h)(randdev);
}
template <> inline double rand<double>(double l, double h) {
  return uniform_real_distribution<double>(l, h)(randdev);
}
template <> inline float rand<float>(float l, float h) {
  return uniform_real_distribution<float>(l, h)(randdev);
}

#if defined(_WIN32) || defined(_WIN64)
#define getchar_unlocked _getchar_nolock
#define putchar_unlocked _putchar_nolock
#elif defined(__GNUC__)
#else
#define getchar_unlocked getchar
#define putchar_unlocked putchar
#endif
namespace {
#define isvisiblechar(c) (0x21 <= (c) && (c) <= 0x7E)
class MaiScanner {
public:
  template <typename T> void input_integer(T &var) {
    var = 0;
    T sign = 1;
    int cc = getchar_unlocked();
    for (; cc < '0' || '9' < cc; cc = getchar_unlocked())
      if (cc == '-')
        sign = -1;
    for (; '0' <= cc && cc <= '9'; cc = getchar_unlocked())
      var = (var << 3) + (var << 1) + cc - '0';
    var = var * sign;
  }
  inline int c() { return getchar_unlocked(); }
  inline MaiScanner &operator>>(int &var) {
    input_integer<int>(var);
    return *this;
  }
  inline MaiScanner &operator>>(long long &var) {
    input_integer<long long>(var);
    return *this;
  }
  inline MaiScanner &operator>>(string &var) {
    int cc = getchar_unlocked();
    for (; !isvisiblechar(cc); cc = getchar_unlocked())
      ;
    for (; isvisiblechar(cc); cc = getchar_unlocked())
      var.push_back(cc);
    return *this;
  }
  template <typename IT> void in(IT begin, IT end) {
    for (auto it = begin; it != end; ++it)
      *this >> *it;
  }
};
class MaiPrinter {
public:
  template <typename T> void output_integer(T var) {
    if (var == 0) {
      putchar_unlocked('0');
      return;
    }
    if (var < 0)
      putchar_unlocked('-'), var = -var;
    char stack[32];
    int stack_p = 0;
    while (var)
      stack[stack_p++] = '0' + (var % 10), var /= 10;
    while (stack_p)
      putchar_unlocked(stack[--stack_p]);
  }
  inline MaiPrinter &operator<<(char c) {
    putchar_unlocked(c);
    return *this;
  }
  inline MaiPrinter &operator<<(int var) {
    output_integer<int>(var);
    return *this;
  }
  inline MaiPrinter &operator<<(long long var) {
    output_integer<long long>(var);
    return *this;
  }
  inline MaiPrinter &operator<<(char *str_p) {
    while (*str_p)
      putchar_unlocked(*(str_p++));
    return *this;
  }
  inline MaiPrinter &operator<<(const string &str) {
    const char *p = str.c_str();
    const char *l = p + str.size();
    while (p < l)
      putchar_unlocked(*p++);
    return *this;
  }
  template <typename IT> void join(IT begin, IT end, char sep = ' ') {
    for (bool b = 0; begin != end; ++begin, b = 1)
      b ? *this << sep << *begin : *this << *begin;
  }
};
} // namespace
MaiScanner scanner;
MaiPrinter printer;

template <typename T> inline T gcd(T a, T b) {
  while (b) {
    T t = a % b;
    a = b;
    b = t;
  }
  return a;
}
template <typename T> inline T lcm(T a, T b) { return a * b / gcd(a, b); }

// MEMO : 逆元...pow_md(n,MOD-2,MOD)
template <typename T> T pow_md(T x, T p, T mod = MD) {
  T y = 1;
  x = x % mod;
  while (0 < p) {
    if (p & 1)
      y = (y * x) % mod;
    x = (x * x) % mod;
    p >>= 1;
  }
  return y;
}
template <typename T> T fact_md(T n, T mod = MD) {
  T p = 1;
  for (; 1 < n; p = (p * n--) % mod)
    ;
  return p;
}
template <typename T> T nPr_md(T n, T r, T mod = MD) {
  T p = 1;
  for (r = n - r; r < n; p = (p * n--) % mod)
    ;
  return p;
}
template <typename T> T nCr_md(T n, T r, T mod = MD) {
  if (n / 2 < r)
    return nCr_md(n, n - r);
  T p = 1;
  for (; 0 < r; r--)
    p = (((p * (n - r + 1)) % mod) * pow_md(r, mod - 2)) % mod;
  return p;
}
template <typename T> inline T nHr_md(T n, T r, T mod = MD) {
  return nCr_md(n - 1 + r, n - 1, mod);
}

template <typename T> T nCr(T n, T r) {
  if (n / 2 < r)
    return nCr(n, n - r);
  T p = 1;
  for (T t = 1; t <= r; ++t)
    p = p * (n - t + 1) / t;
  return p;
}
template <typename T> inline T nHr(T n, T r, T mod = MD) {
  return nCr(n - 1 + r, n - 1, mod);
}

// 1周をmodで表現するような角度の単位系で，
// 角度xから角度yへ向きを変えるとき，xに加算するべき値
inline double diffangle(double x, double y, double mod) {
  double a1 = fmod(y - x, mod), a2 = fmod(y - x + mod, mod),
         a3 = fmod(y - x - mod, mod);
  return abs(a2) < abs(a1) ? (abs(a3) < abs(a2) ? a3 : a2)
                           : (abs(a3) < abs(a1) ? a3 : a1);
}

/*

A = Bならば？
K/A個塗る．A+Bでも濡れるので…

Aの個数を固定＝＞Bも決まる
＝＞O(N^2)


*/

ll N, A, B, K;

ll table_nCr[300010];

int main() {

  scanner >> N >> A >> B >> K;

  table_nCr[0] = 1;
  iterate(r, 1ll, N + 5) {
    table_nCr[r] =
        ((((table_nCr[r - 1] * (N - r + 1)) % MD) * pow_md(r, MD - 2, MD))) %
        MD;
  }

  ll ans = 0;

  repeat(a, N + 1) {
    // Bで塗る必要がある個数
    ll rem = K - a * A;
    if (rem % B)
      continue;
    ll b = rem / B;

    if (a > N || b > N)
      continue;
    ans += table_nCr[a] * table_nCr[b];
    ans %= MD;
  }

  cout << ans << endl;

  return 0;
}

Fixed submission:
#pragma GCC optimize("O3")
#include "bits/stdc++.h"

using namespace std;
using ll = long long int;

#define debug(v)                                                               \
  {                                                                            \
    printf("L%d %s > ", __LINE__, #v);                                         \
    cout << (v) << endl;                                                       \
  }
#define debugv(v)                                                              \
  {                                                                            \
    printf("L%d %s > ", __LINE__, #v);                                         \
    for (auto e : (v)) {                                                       \
      cout << e << " ";                                                        \
    }                                                                          \
    cout << endl;                                                              \
  }
#define debuga(m, w)                                                           \
  {                                                                            \
    printf("L%d %s > ", __LINE__, #m);                                         \
    for (int x = 0; x < (w); x++) {                                            \
      cout << (m)[x] << " ";                                                   \
    }                                                                          \
    cout << endl;                                                              \
  }
#define debugaa(m, h, w)                                                       \
  {                                                                            \
    printf("L%d %s >\n", __LINE__, #m);                                        \
    for (int y = 0; y < (h); y++) {                                            \
      for (int x = 0; x < (w); x++) {                                          \
        cout << (m)[y][x] << " ";                                              \
      }                                                                        \
      cout << endl;                                                            \
    }                                                                          \
  }
#define ALL(v) (v).begin(), (v).end()
#define repeat(cnt, l)                                                         \
  for (remove_const<decltype(l)>::type cnt = 0; (cnt) < (l); ++(cnt))
#define rrepeat(cnt, l) for (auto cnt = (l)-1; 0 <= (cnt); --(cnt))
#define iterate(cnt, b, e) for (auto cnt = (b); (cnt) != (e); ++(cnt))
#define diterate(cnt, b, e) for (auto cnt = (b); (cnt) != (e); --(cnt))
const ll MD = 998244353ll;
const long double PI = 3.1415926535897932384626433832795L;
inline void assert_call(bool assertion, function<void()> f) {
  if (!assertion) {
    cerr << "assertion fault:" << endl;
    f();
    abort();
  }
}
template <typename T1, typename T2>
inline ostream &operator<<(ostream &o, const pair<T1, T2> p) {
  o << '(' << p.first << ':' << p.second << ')';
  return o;
}
template <typename Vec>
inline ostream &_ostream_vecprint(ostream &o, const Vec &p) {
  o << '[';
  for (auto &e : p)
    o << e << ',';
  o << ']';
  return o;
}
template <typename T>
inline ostream &operator<<(ostream &o, const vector<T> &v) {
  return _ostream_vecprint(o, v);
}
template <typename T, size_t S>
inline ostream &operator<<(ostream &o, const array<T, S> &v) {
  return _ostream_vecprint(o, v);
}
template <typename T> inline T &maxset(T &to, const T &val) {
  return to = max(to, val);
}
template <typename T> inline T &minset(T &to, const T &val) {
  return to = min(to, val);
}
void bye(string s, int code = 0) {
  cout << s << endl;
  exit(code);
}
mt19937_64 randdev(8901016);
template <typename T> inline T rand(T l, T h) {
  return uniform_int_distribution<T>(l, h)(randdev);
}
template <> inline double rand<double>(double l, double h) {
  return uniform_real_distribution<double>(l, h)(randdev);
}
template <> inline float rand<float>(float l, float h) {
  return uniform_real_distribution<float>(l, h)(randdev);
}

#if defined(_WIN32) || defined(_WIN64)
#define getchar_unlocked _getchar_nolock
#define putchar_unlocked _putchar_nolock
#elif defined(__GNUC__)
#else
#define getchar_unlocked getchar
#define putchar_unlocked putchar
#endif
namespace {
#define isvisiblechar(c) (0x21 <= (c) && (c) <= 0x7E)
class MaiScanner {
public:
  template <typename T> void input_integer(T &var) {
    var = 0;
    T sign = 1;
    int cc = getchar_unlocked();
    for (; cc < '0' || '9' < cc; cc = getchar_unlocked())
      if (cc == '-')
        sign = -1;
    for (; '0' <= cc && cc <= '9'; cc = getchar_unlocked())
      var = (var << 3) + (var << 1) + cc - '0';
    var = var * sign;
  }
  inline int c() { return getchar_unlocked(); }
  inline MaiScanner &operator>>(int &var) {
    input_integer<int>(var);
    return *this;
  }
  inline MaiScanner &operator>>(long long &var) {
    input_integer<long long>(var);
    return *this;
  }
  inline MaiScanner &operator>>(string &var) {
    int cc = getchar_unlocked();
    for (; !isvisiblechar(cc); cc = getchar_unlocked())
      ;
    for (; isvisiblechar(cc); cc = getchar_unlocked())
      var.push_back(cc);
    return *this;
  }
  template <typename IT> void in(IT begin, IT end) {
    for (auto it = begin; it != end; ++it)
      *this >> *it;
  }
};
class MaiPrinter {
public:
  template <typename T> void output_integer(T var) {
    if (var == 0) {
      putchar_unlocked('0');
      return;
    }
    if (var < 0)
      putchar_unlocked('-'), var = -var;
    char stack[32];
    int stack_p = 0;
    while (var)
      stack[stack_p++] = '0' + (var % 10), var /= 10;
    while (stack_p)
      putchar_unlocked(stack[--stack_p]);
  }
  inline MaiPrinter &operator<<(char c) {
    putchar_unlocked(c);
    return *this;
  }
  inline MaiPrinter &operator<<(int var) {
    output_integer<int>(var);
    return *this;
  }
  inline MaiPrinter &operator<<(long long var) {
    output_integer<long long>(var);
    return *this;
  }
  inline MaiPrinter &operator<<(char *str_p) {
    while (*str_p)
      putchar_unlocked(*(str_p++));
    return *this;
  }
  inline MaiPrinter &operator<<(const string &str) {
    const char *p = str.c_str();
    const char *l = p + str.size();
    while (p < l)
      putchar_unlocked(*p++);
    return *this;
  }
  template <typename IT> void join(IT begin, IT end, char sep = ' ') {
    for (bool b = 0; begin != end; ++begin, b = 1)
      b ? *this << sep << *begin : *this << *begin;
  }
};
} // namespace
MaiScanner scanner;
MaiPrinter printer;

template <typename T> inline T gcd(T a, T b) {
  while (b) {
    T t = a % b;
    a = b;
    b = t;
  }
  return a;
}
template <typename T> inline T lcm(T a, T b) { return a * b / gcd(a, b); }

// MEMO : 逆元...pow_md(n,MOD-2,MOD)
template <typename T> T pow_md(T x, T p, T mod = MD) {
  T y = 1;
  x = x % mod;
  while (0 < p) {
    if (p & 1)
      y = (y * x) % mod;
    x = (x * x) % mod;
    p >>= 1;
  }
  return y;
}
template <typename T> T fact_md(T n, T mod = MD) {
  T p = 1;
  for (; 1 < n; p = (p * n--) % mod)
    ;
  return p;
}
template <typename T> T nPr_md(T n, T r, T mod = MD) {
  T p = 1;
  for (r = n - r; r < n; p = (p * n--) % mod)
    ;
  return p;
}
template <typename T> T nCr_md(T n, T r, T mod = MD) {
  if (n / 2 < r)
    return nCr_md(n, n - r);
  T p = 1;
  for (; 0 < r; r--)
    p = (((p * (n - r + 1)) % mod) * pow_md(r, mod - 2)) % mod;
  return p;
}
template <typename T> inline T nHr_md(T n, T r, T mod = MD) {
  return nCr_md(n - 1 + r, n - 1, mod);
}

template <typename T> T nCr(T n, T r) {
  if (n / 2 < r)
    return nCr(n, n - r);
  T p = 1;
  for (T t = 1; t <= r; ++t)
    p = p * (n - t + 1) / t;
  return p;
}
template <typename T> inline T nHr(T n, T r, T mod = MD) {
  return nCr(n - 1 + r, n - 1, mod);
}

// 1周をmodで表現するような角度の単位系で，
// 角度xから角度yへ向きを変えるとき，xに加算するべき値
inline double diffangle(double x, double y, double mod) {
  double a1 = fmod(y - x, mod), a2 = fmod(y - x + mod, mod),
         a3 = fmod(y - x - mod, mod);
  return abs(a2) < abs(a1) ? (abs(a3) < abs(a2) ? a3 : a2)
                           : (abs(a3) < abs(a1) ? a3 : a1);
}

/*

A = Bならば？
K/A個塗る．A+Bでも濡れるので…

Aの個数を固定＝＞Bも決まる
＝＞O(N^2)


*/

ll N, A, B, K;

ll table_nCr[300010];

int main() {

  scanner >> N >> A >> B >> K;

  table_nCr[0] = 1;
  iterate(r, 1ll, N + 5) {
    table_nCr[r] =
        ((((table_nCr[r - 1] * (N - r + 1)) % MD) * pow_md(r, MD - 2, MD))) %
        MD;
  }

  ll ans = 0;

  repeat(a, N + 1) {
    // Bで塗る必要がある個数
    ll rem = K - a * A;
    if (rem < 0 || rem % B)
      continue;
    ll b = rem / B;

    if (a > N || b > N)
      continue;
    ans += table_nCr[a] * table_nCr[b];
    ans %= MD;
  }

  cout << ans << endl;

  return 0;
}