Problem p02634 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using ull = unsigned long long;
using uint = unsigned;
using pcc = pair<char, char>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pdd = pair<double, double>;
using tuplis = array<ll, 3>;
template <class T> using pq = priority_queue<T, vector<T>, greater<T>>;
const ll LINF = 0x1fffffffffffffff;
const ll MINF = 0x7fffffffffff;
const int INF = 0x3fffffff;
const int MOD = 1000000007;
const int MODD = 998244353;
const ld DINF = numeric_limits<ld>::infinity();
const ld EPS = 1e-9;
const ld PI = 3.1415926535897932;
const ll dx[] = {0, 1, 0, -1, 1, -1, 1, -1};
const ll dy[] = {1, 0, -1, 0, 1, 1, -1, -1};
#define overload4(_1, _2, _3, _4, name, ...) name
#define overload3(_1, _2, _3, name, ...) name
#define rep1(n) for (ll i = 0; i < n; ++i)
#define rep2(i, n) for (ll i = 0; i < n; ++i)
#define rep3(i, a, b) for (ll i = a; i < b; ++i)
#define rep4(i, a, b, c) for (ll i = a; i < b; i += c)
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)
#define rrep1(n) for (ll i = (n); i--;)
#define rrep2(i, n) for (ll i = (n); i--;)
#define rrep3(i, a, b) for (ll i = (b); i-- > (a);)
#define rrep4(i, a, b, c) for (ll i = a + (b - a - 1) / c * c; i >= a; i -= c)
#define rrep(...)                                                              \\
  overload4(__VA_ARGS__, rrep4, rrep3, rrep2, rrep1)(__VA_ARGS__)
#define each1(i, a) for (auto &&i : a)
#define each2(x, y, a) for (auto &&[x, y] : a)
#define each3(x, y, z, a) for (auto &&[x, y, z] : a)
#define each(...) overload4(__VA_ARGS__, each3, each2, each1)(__VA_ARGS__)
#define all1(i) begin(i), end(i)
#define all2(i, a) begin(i), begin(i) + a
#define all3(i, a, b) begin(i) + a, begin(i) + b
#define all(...) overload3(__VA_ARGS__, all3, all2, all1)(__VA_ARGS__)
#define rall1(i) (i).rbegin(), (i).rend()
#define rall2(i, k) (i).rbegin(), (i).rbegin() + k
#define rall3(i, a, b) (i).rbegin() + a, (i).rbegin() + b
#define rall(...) overload3(__VA_ARGS__, rall3, rall2, rall1)(__VA_ARGS__)
#define sum(...) accumulate(all(__VA_ARGS__), 0LL)
#define dsum(...) accumulate(all(__VA_ARGS__), 0.0L)
#define elif else if
#define unless(a) if (!(a))
#define mp make_pair
#define mt make_tuple
#define INT(...)                                                               \\
  int __VA_ARGS__;                                                             \\
  in(__VA_ARGS__)
#define LL(...)                                                                \\
  ll __VA_ARGS__;                                                              \\
  in(__VA_ARGS__)
#define ULL(...)                                                               \\
  ull __VA_ARGS__;                                                             \\
  in(__VA_ARGS__)
#define STR(...)                                                               \\
  string __VA_ARGS__;                                                          \\
  in(__VA_ARGS__)
#define CHR(...)                                                               \\
  char __VA_ARGS__;                                                            \\
  in(__VA_ARGS__)
#define DBL(...)                                                               \\
  double __VA_ARGS__;                                                          \\
  in(__VA_ARGS__)
#define LD(...)                                                                \\
  ld __VA_ARGS__;                                                              \\
  in(__VA_ARGS__)
#define Sort(a) sort(all(a))
#define Rev(a) reverse(all(a))
#define Uniq(a)                                                                \\
  sort(all(a));                                                                \\
  a.erase(unique(all(a)), end(a))
#define vec(type, name, ...) vector<type> name(__VA_ARGS__)
#define VEC(type, name, size)                                                  \\
  vector<type> name(size);                                                     \\
  in(name)
#define vv(type, name, h, ...)                                                 \\
  vector<vector<type>> name(h, vector<type>(__VA_ARGS__))
#define VV(type, name, h, w)                                                   \\
  vector<vector<type>> name(h, vector<type>(w));                               \\
  in(name)
#define vvv(type, name, h, w, ...)                                             \\
  vector<vector<vector<type>>> name(                                           \\
      h, vector<vector<type>>(w, vector<type>(__VA_ARGS__)))
template <class T> auto min(const T &a) { return *min_element(all(a)); }
template <class T> auto max(const T &a) { return *max_element(all(a)); }
inline ll popcnt(ull a) { return __builtin_popcountll(a); }
ll gcd(ll a, ll b) {
  while (b) {
    ll c = b;
    b = a % b;
    a = c;
  }
  return a;
}
ll lcm(ll a, ll b) {
  if (!a || !b)
    return 0;
  return a * b / gcd(a, b);
}
ll intpow(ll a, ll b) {
  ll ans = 1;
  while (b) {
    if (b & 1)
      ans *= a;
    a *= a;
    b /= 2;
  }
  return ans;
}
ll modpow(ll a, ll b, ll p) {
  ll ans = 1;
  while (b) {
    if (b & 1)
      (ans *= a) %= p;
    (a *= a) %= p;
    b /= 2;
  }
  return ans;
}
template <class T, class U> bool chmin(T &a, const U &b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T, class U> bool chmax(T &a, const U &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
vector<ll> iota(ll n) {
  vector<ll> a(n);
  iota(a.begin(), a.end(), 0);
  return a;
}
vector<pll> factor(ull x) {
  vector<pll> ans;
  for (ll i = 2; i * i <= x; i++)
    if (x % i == 0) {
      ans.push_back({i, 1});
      while ((x /= i) % i == 0)
        ans.back().second++;
    }
  if (x != 1)
    ans.push_back({x, 1});
  return ans;
}
map<ll, ll> factor_map(ull x) {
  map<ll, ll> ans;
  for (ll i = 2; i * i <= x; i++)
    if (x % i == 0) {
      ans[i] = 1;
      while ((x /= i) % i == 0)
        ans[i]++;
    }
  if (x != 1)
    ans[x] = 1;
  return ans;
}
vector<uint> divisor(uint x) {
  vector<uint> ans;
  for (uint i = 1; i * i <= x; i++)
    if (x % i == 0)
      ans.push_back(i);
  rrep(ans.size() - (ans.back() * ans.back() == x)) ans.push_back(x / ans[i]);
  return ans;
}
template <class T> unordered_map<T, ll> press(vector<T> &a) {
  auto b = a;
  sort(all(b));
  b.erase(unique(all(b)), b.end());
  unordered_map<T, ll> ans;
  rep(b.size()) ans[b[i]] = i;
  each(i, a) i = ans[i];
  return ans;
}
template <class T> map<T, ll> press_map(vector<T> &a) {
  auto b = a;
  sort(all(b));
  b.erase(unique(all(b)), b.end());
  map<T, ll> ans;
  rep(b.size()) ans[b[i]] = i;
  each(i, a) i = ans[i];
  return ans;
}
int scan() { return getchar(); }
void scan(int &a) { scanf("%d", &a); }
void scan(unsigned &a) { scanf("%u", &a); }
void scan(long &a) { scanf("%ld", &a); }
void scan(long long &a) { scanf("%lld", &a); }
void scan(unsigned long long &a) { scanf("%llu", &a); }
void scan(char &a) {
  do {
    a = getchar();
  } while (a == ' ' || a == '\\n');
}
void scan(float &a) { scanf("%f", &a); }
void scan(double &a) { scanf("%lf", &a); }
void scan(long double &a) { scanf("%Lf", &a); }
void scan(vector<bool> &a) {
  for (unsigned i = 0; i < a.size(); i++) {
    int b;
    scan(b);
    a[i] = b;
  }
}
void scan(char a[]) { scanf("%s", a); }
void scan(string &a) { cin >> a; }
template <class T> void scan(vector<T> &);
template <class T, size_t size> void scan(array<T, size> &);
template <class T, class L> void scan(pair<T, L> &);
template <class T, size_t size> void scan(T (&)[size]);
template <class T> void scan(vector<T> &a) {
  for (auto &&i : a)
    scan(i);
}
template <class T> void scan(deque<T> &a) {
  for (auto &&i : a)
    scan(i);
}
template <class T, size_t size> void scan(array<T, size> &a) {
  for (auto &&i : a)
    scan(i);
}
template <class T, class L> void scan(pair<T, L> &p) {
  scan(p.first);
  scan(p.second);
}
template <class T, size_t size> void scan(T (&a)[size]) {
  for (auto &&i : a)
    scan(i);
}
template <class T> void scan(T &a) { cin >> a; }
void in() {}
template <class Head, class... Tail> void in(Head &head, Tail &...tail) {
  scan(head);
  in(tail...);
}
void print() { putchar(' '); }
void print(bool a) { printf("%d", a); }
void print(int a) { printf("%d", a); }
void print(unsigned a) { printf("%u", a); }
void print(long a) { printf("%ld", a); }
void print(long long a) { printf("%lld", a); }
void print(unsigned long long a) { printf("%llu", a); }
void print(char a) { printf("%c", a); }
void print(char a[]) { printf("%s", a); }
void print(const char a[]) { printf("%s", a); }
void print(float a) { printf("%.15f", a); }
void print(double a) { printf("%.15f", a); }
void print(long double a) { printf("%.15Lf", a); }
void print(const string &a) {
  for (auto &&i : a)
    print(i);
}
template <class T> void print(const vector<T> &);
template <class T, size_t size> void print(const array<T, size> &);
template <class T, class L> void print(const pair<T, L> &p);
template <class T, size_t size> void print(const T (&)[size]);
template <class T> void print(const vector<T> &a) {
  if (a.empty())
    return;
  print(a[0]);
  for (auto i = a.begin(); ++i != a.end();) {
    putchar(' ');
    print(*i);
  }
}
template <class T> void print(const deque<T> &a) {
  if (a.empty())
    return;
  print(a[0]);
  for (auto i = a.begin(); ++i != a.end();) {
    putchar(' ');
    print(*i);
  }
}
template <class T, size_t size> void print(const array<T, size> &a) {
  print(a[0]);
  for (auto i = a.begin(); ++i != a.end();) {
    putchar(' ');
    print(*i);
  }
}
template <class T, class L> void print(const pair<T, L> &p) {
  print(p.first);
  putchar(' ');
  print(p.second);
}
template <class T, size_t size> void print(const T (&a)[size]) {
  print(a[0]);
  for (auto i = a; ++i != end(a);) {
    putchar(' ');
    print(*i);
  }
}
template <class T> void print(const T &a) { cout << a; }
int out() {
  putchar('\\n');
  return 0;
}
template <class T> int out(const T &t) {
  print(t);
  putchar('\\n');
  return 0;
}
template <class Head, class... Tail>
int out(const Head &head, const Tail &...tail) {
  print(head);
  putchar(' ');
  out(tail...);
  return 0;
}
#ifdef DEBUG
inline ll __lg(ull __n) {
  return sizeof(ull) * __CHAR_BIT__ - 1 - __builtin_clzll(__n);
}
#define debug(...)                                                             \\
  {                                                                            \\
    print(#__VA_ARGS__);                                                       \\
    print(":");                                                                \\
    out(__VA_ARGS__);                                                          \\
  }
#else
#define debug(...) void(0)
#endif
int first(bool i = true) { return out(i ? "first" : "second"); }
int yes(bool i = true) { return out(i ? "yes" : "no"); }
int Yes(bool i = true) { return out(i ? "Yes" : "No"); }
int No() { return out("No"); }
int YES(bool i = true) { return out(i ? "YES" : "NO"); }
int NO() { return out("NO"); }
int Yay(bool i = true) { return out(i ? "Yay!" : ":("); }
int possible(bool i = true) { return out(i ? "possible" : "impossible"); }
int Possible(bool i = true) { return out(i ? "Possible" : "Impossible"); }
int POSSIBLE(bool i = true) { return out(i ? "POSSIBLE" : "IMPOSSIBLE"); }
void Case(ll i) { printf("Case #%lld: ", i); }

constexpr uint mod = MODD;
struct Modint {
  uint num = 0;
  constexpr Modint() noexcept {}
  constexpr Modint(const Modint &x) noexcept : num(x.num) {}
  inline constexpr operator ll() const noexcept { return num; }
  inline constexpr Modint &operator+=(Modint x) noexcept {
    num += x.num;
    if (num >= mod)
      num -= mod;
    return *this;
  }
  inline constexpr Modint &operator++() noexcept {
    if (num == mod - 1)
      num = 0;
    else
      num++;
    return *this;
  }
  inline constexpr Modint operator++(int) noexcept {
    Modint ans(*this);
    operator++();
    return ans;
  }
  inline constexpr Modint operator-() const noexcept {
    return Modint(0) -= *this;
  }
  inline constexpr Modint operator-(Modint x) const noexcept {
    return Modint(*this) -= x;
  }
  inline constexpr Modint &operator-=(Modint x) noexcept {
    if (num < x.num)
      num += mod;
    num -= x.num;
    return *this;
  }
  inline constexpr Modint &operator--() noexcept {
    if (num == 0)
      num = mod - 1;
    else
      num--;
    return *this;
  }
  inline constexpr Modint operator--(int) noexcept {
    Modint ans(*this);
    operator--();
    return ans;
  }
  inline constexpr Modint &operator*=(Modint x) noexcept {
    num = ull(num) * x.num % mod;
    return *this;
  }
  inline constexpr Modint &operator/=(Modint x) noexcept {
    return operator*=(x.inv());
  }
  template <class T> constexpr Modint(T x) noexcept {
    using U = typename conditional<sizeof(T) >= 4, T, int>::type;
    U y = x;
    y %= U(mod);
    if (y < 0)
      y += mod;
    num = uint(y);
  }
  template <class T> inline constexpr Modint operator+(T x) const noexcept {
    return Modint(*this) += x;
  }
  template <class T> inline constexpr Modint &operator+=(T x) noexcept {
    return operator+=(Modint(x));
  }
  template <class T> inline constexpr Modint operator-(T x) const noexcept {
    return Modint(*this) -= x;
  }
  template <class T> inline constexpr Modint &operator-=(T x) noexcept {
    return operator-=(Modint(x));
  }
  template <class T> inline constexpr Modint operator*(T x) const noexcept {
    return Modint(*this) *= x;
  }
  template <class T> inline constexpr Modint &operator*=(T x) noexcept {
    return operator*=(Modint(x));
  }
  template <class T> inline constexpr Modint operator/(T x) const noexcept {
    return Modint(*this) /= x;
  }
  template <class T> inline constexpr Modint &operator/=(T x) noexcept {
    return operator/=(Modint(x));
  }
  inline constexpr Modint inv() const noexcept {
    ll x = 0, y = 0;
    extgcd(num, mod, x, y);
    return x;
  }
  static inline constexpr ll extgcd(ll a, ll b, ll &x, ll &y) noexcept {
    ll g = a;
    x = 1;
    y = 0;
    if (b) {
      g = extgcd(b, a % b, y, x);
      y -= a / b * x;
    }
    return g;
  }
  inline constexpr Modint pow(ull x) const noexcept {
    Modint ans = 1, cnt = *this;
    while (x) {
      if (x & 1)
        ans *= cnt;
      cnt *= cnt;
      x /= 2;
    }
    return ans;
  }
};
std::istream &operator>>(std::istream &is, Modint &x) {
  ll a;
  in(a);
  x = a;
  return is;
}
inline constexpr Modint operator""_M(ull x) noexcept { return Modint(x); }
std::vector<Modint> fac(1, 1), inv(1, 1);
inline void reserve(ll a) {
  if (fac.size() >= a)
    return;
  if (a < fac.size() * 2)
    a = fac.size() * 2;
  if (a >= mod)
    a = mod;
  while (fac.size() < a)
    fac.push_back(fac.back() * Modint(fac.size()));
  inv.resize(fac.size());
  inv.back() = fac.back().inv();
  for (ll i = inv.size() - 1; !inv[i - 1]; i--)
    inv[i - 1] = inv[i] * i;
}
inline Modint fact(ll n) {
  if (n < 0)
    return 0;
  reserve(n + 1);
  return fac[n];
}
inline Modint perm(ll n, ll r) {
  if (r < 0 || n < r)
    return 0;
  if (n >> 24) {
    Modint ans = 1;
    for (ll i = 0; i < r; i++)
      ans *= n--;
    return ans;
  }
  reserve(n + 1);
  return fac[n] * inv[n - r];
}
inline Modint comb(ll n, ll r) {
  if (r < 0 || n < r)
    return 0;
  reserve(r + 1);
  return perm(n, r) * inv[r];
}
inline Modint Mcomb(ll n, ll r) {
  return comb(n + r - 1, n - 1);
} // r balls into n boxes
inline Modint catalan(ll n) {
  reserve(n * 2 + 1);
  return fac[n * 2] * inv[n] * inv[n + 1];
}
Modint mem[3001][3001], mem1[3001][3001], mem2[3001][3001];
ll a, b, c, d;
Modint dp1(ll c, ll d);
Modint dp2(ll c, ll d);
Modint dp(ll c, ll d) {
  if (mem[c][d].num != uint(-1))
    return mem[c][d];
  if (c < a || d < b)
    return 0;
  if (c == a && d == b)
    return mem[c][d] = 1;
  if (c == a)
    return mem[c][d] = dp(c, d - 1) * c;
  if (d == b)
    return mem[c][d] = dp(c - 1, d) * d;
  return mem[c][d] = dp(c - 1, d - 1) * (c - 1) * (d - 1) + dp1(c - 1, d - 1) +
                     dp2(c - 1, d - 1);
}
Modint dp1(ll c, ll d) {
  if (mem1[c][d].num != uint(-1))
    return mem1[c][d];
  if (c < a || d < b)
    return 0;
  return mem1[c][d] = dp1(c - 1, d) * (d + 1) + dp(c, d) * c;
}
Modint dp2(ll c, ll d) {
  if (mem2[c][d].num != uint(-1))
    return mem2[c][d];
  if (c < a || d < b)
    return 0;
  return mem2[c][d] = dp2(c, d - 1) * (c + 1) + dp(c, d) * d;
}
signed main() {
  memset(mem, 0xff, sizeof(mem));
  memset(mem1, 0xff, sizeof(mem1));
  memset(mem2, 0xff, sizeof(mem2));
  in(a, b, c, d);
  out(dp(c, d));
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using ull = unsigned long long;
using uint = unsigned;
using pcc = pair<char, char>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pdd = pair<double, double>;
using tuplis = array<ll, 3>;
template <class T> using pq = priority_queue<T, vector<T>, greater<T>>;
const ll LINF = 0x1fffffffffffffff;
const ll MINF = 0x7fffffffffff;
const int INF = 0x3fffffff;
const int MOD = 1000000007;
const int MODD = 998244353;
const ld DINF = numeric_limits<ld>::infinity();
const ld EPS = 1e-9;
const ld PI = 3.1415926535897932;
const ll dx[] = {0, 1, 0, -1, 1, -1, 1, -1};
const ll dy[] = {1, 0, -1, 0, 1, 1, -1, -1};
#define overload4(_1, _2, _3, _4, name, ...) name
#define overload3(_1, _2, _3, name, ...) name
#define rep1(n) for (ll i = 0; i < n; ++i)
#define rep2(i, n) for (ll i = 0; i < n; ++i)
#define rep3(i, a, b) for (ll i = a; i < b; ++i)
#define rep4(i, a, b, c) for (ll i = a; i < b; i += c)
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)
#define rrep1(n) for (ll i = (n); i--;)
#define rrep2(i, n) for (ll i = (n); i--;)
#define rrep3(i, a, b) for (ll i = (b); i-- > (a);)
#define rrep4(i, a, b, c) for (ll i = a + (b - a - 1) / c * c; i >= a; i -= c)
#define rrep(...)                                                              \\
  overload4(__VA_ARGS__, rrep4, rrep3, rrep2, rrep1)(__VA_ARGS__)
#define each1(i, a) for (auto &&i : a)
#define each2(x, y, a) for (auto &&[x, y] : a)
#define each3(x, y, z, a) for (auto &&[x, y, z] : a)
#define each(...) overload4(__VA_ARGS__, each3, each2, each1)(__VA_ARGS__)
#define all1(i) begin(i), end(i)
#define all2(i, a) begin(i), begin(i) + a
#define all3(i, a, b) begin(i) + a, begin(i) + b
#define all(...) overload3(__VA_ARGS__, all3, all2, all1)(__VA_ARGS__)
#define rall1(i) (i).rbegin(), (i).rend()
#define rall2(i, k) (i).rbegin(), (i).rbegin() + k
#define rall3(i, a, b) (i).rbegin() + a, (i).rbegin() + b
#define rall(...) overload3(__VA_ARGS__, rall3, rall2, rall1)(__VA_ARGS__)
#define sum(...) accumulate(all(__VA_ARGS__), 0LL)
#define dsum(...) accumulate(all(__VA_ARGS__), 0.0L)
#define elif else if
#define unless(a) if (!(a))
#define mp make_pair
#define mt make_tuple
#define INT(...)                                                               \\
  int __VA_ARGS__;                                                             \\
  in(__VA_ARGS__)
#define LL(...)                                                                \\
  ll __VA_ARGS__;                                                              \\
  in(__VA_ARGS__)
#define ULL(...)                                                               \\
  ull __VA_ARGS__;                                                             \\
  in(__VA_ARGS__)
#define STR(...)                                                               \\
  string __VA_ARGS__;                                                          \\
  in(__VA_ARGS__)
#define CHR(...)                                                               \\
  char __VA_ARGS__;                                                            \\
  in(__VA_ARGS__)
#define DBL(...)                                                               \\
  double __VA_ARGS__;                                                          \\
  in(__VA_ARGS__)
#define LD(...)                                                                \\
  ld __VA_ARGS__;                                                              \\
  in(__VA_ARGS__)
#define Sort(a) sort(all(a))
#define Rev(a) reverse(all(a))
#define Uniq(a)                                                                \\
  sort(all(a));                                                                \\
  a.erase(unique(all(a)), end(a))
#define vec(type, name, ...) vector<type> name(__VA_ARGS__)
#define VEC(type, name, size)                                                  \\
  vector<type> name(size);                                                     \\
  in(name)
#define vv(type, name, h, ...)                                                 \\
  vector<vector<type>> name(h, vector<type>(__VA_ARGS__))
#define VV(type, name, h, w)                                                   \\
  vector<vector<type>> name(h, vector<type>(w));                               \\
  in(name)
#define vvv(type, name, h, w, ...)                                             \\
  vector<vector<vector<type>>> name(                                           \\
      h, vector<vector<type>>(w, vector<type>(__VA_ARGS__)))
template <class T> auto min(const T &a) { return *min_element(all(a)); }
template <class T> auto max(const T &a) { return *max_element(all(a)); }
inline ll popcnt(ull a) { return __builtin_popcountll(a); }
ll gcd(ll a, ll b) {
  while (b) {
    ll c = b;
    b = a % b;
    a = c;
  }
  return a;
}
ll lcm(ll a, ll b) {
  if (!a || !b)
    return 0;
  return a * b / gcd(a, b);
}
ll intpow(ll a, ll b) {
  ll ans = 1;
  while (b) {
    if (b & 1)
      ans *= a;
    a *= a;
    b /= 2;
  }
  return ans;
}
ll modpow(ll a, ll b, ll p) {
  ll ans = 1;
  while (b) {
    if (b & 1)
      (ans *= a) %= p;
    (a *= a) %= p;
    b /= 2;
  }
  return ans;
}
template <class T, class U> bool chmin(T &a, const U &b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T, class U> bool chmax(T &a, const U &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
vector<ll> iota(ll n) {
  vector<ll> a(n);
  iota(a.begin(), a.end(), 0);
  return a;
}
vector<pll> factor(ull x) {
  vector<pll> ans;
  for (ll i = 2; i * i <= x; i++)
    if (x % i == 0) {
      ans.push_back({i, 1});
      while ((x /= i) % i == 0)
        ans.back().second++;
    }
  if (x != 1)
    ans.push_back({x, 1});
  return ans;
}
map<ll, ll> factor_map(ull x) {
  map<ll, ll> ans;
  for (ll i = 2; i * i <= x; i++)
    if (x % i == 0) {
      ans[i] = 1;
      while ((x /= i) % i == 0)
        ans[i]++;
    }
  if (x != 1)
    ans[x] = 1;
  return ans;
}
vector<uint> divisor(uint x) {
  vector<uint> ans;
  for (uint i = 1; i * i <= x; i++)
    if (x % i == 0)
      ans.push_back(i);
  rrep(ans.size() - (ans.back() * ans.back() == x)) ans.push_back(x / ans[i]);
  return ans;
}
template <class T> unordered_map<T, ll> press(vector<T> &a) {
  auto b = a;
  sort(all(b));
  b.erase(unique(all(b)), b.end());
  unordered_map<T, ll> ans;
  rep(b.size()) ans[b[i]] = i;
  each(i, a) i = ans[i];
  return ans;
}
template <class T> map<T, ll> press_map(vector<T> &a) {
  auto b = a;
  sort(all(b));
  b.erase(unique(all(b)), b.end());
  map<T, ll> ans;
  rep(b.size()) ans[b[i]] = i;
  each(i, a) i = ans[i];
  return ans;
}
int scan() { return getchar(); }
void scan(int &a) { scanf("%d", &a); }
void scan(unsigned &a) { scanf("%u", &a); }
void scan(long &a) { scanf("%ld", &a); }
void scan(long long &a) { scanf("%lld", &a); }
void scan(unsigned long long &a) { scanf("%llu", &a); }
void scan(char &a) {
  do {
    a = getchar();
  } while (a == ' ' || a == '\\n');
}
void scan(float &a) { scanf("%f", &a); }
void scan(double &a) { scanf("%lf", &a); }
void scan(long double &a) { scanf("%Lf", &a); }
void scan(vector<bool> &a) {
  for (unsigned i = 0; i < a.size(); i++) {
    int b;
    scan(b);
    a[i] = b;
  }
}
void scan(char a[]) { scanf("%s", a); }
void scan(string &a) { cin >> a; }
template <class T> void scan(vector<T> &);
template <class T, size_t size> void scan(array<T, size> &);
template <class T, class L> void scan(pair<T, L> &);
template <class T, size_t size> void scan(T (&)[size]);
template <class T> void scan(vector<T> &a) {
  for (auto &&i : a)
    scan(i);
}
template <class T> void scan(deque<T> &a) {
  for (auto &&i : a)
    scan(i);
}
template <class T, size_t size> void scan(array<T, size> &a) {
  for (auto &&i : a)
    scan(i);
}
template <class T, class L> void scan(pair<T, L> &p) {
  scan(p.first);
  scan(p.second);
}
template <class T, size_t size> void scan(T (&a)[size]) {
  for (auto &&i : a)
    scan(i);
}
template <class T> void scan(T &a) { cin >> a; }
void in() {}
template <class Head, class... Tail> void in(Head &head, Tail &...tail) {
  scan(head);
  in(tail...);
}
void print() { putchar(' '); }
void print(bool a) { printf("%d", a); }
void print(int a) { printf("%d", a); }
void print(unsigned a) { printf("%u", a); }
void print(long a) { printf("%ld", a); }
void print(long long a) { printf("%lld", a); }
void print(unsigned long long a) { printf("%llu", a); }
void print(char a) { printf("%c", a); }
void print(char a[]) { printf("%s", a); }
void print(const char a[]) { printf("%s", a); }
void print(float a) { printf("%.15f", a); }
void print(double a) { printf("%.15f", a); }
void print(long double a) { printf("%.15Lf", a); }
void print(const string &a) {
  for (auto &&i : a)
    print(i);
}
template <class T> void print(const vector<T> &);
template <class T, size_t size> void print(const array<T, size> &);
template <class T, class L> void print(const pair<T, L> &p);
template <class T, size_t size> void print(const T (&)[size]);
template <class T> void print(const vector<T> &a) {
  if (a.empty())
    return;
  print(a[0]);
  for (auto i = a.begin(); ++i != a.end();) {
    putchar(' ');
    print(*i);
  }
}
template <class T> void print(const deque<T> &a) {
  if (a.empty())
    return;
  print(a[0]);
  for (auto i = a.begin(); ++i != a.end();) {
    putchar(' ');
    print(*i);
  }
}
template <class T, size_t size> void print(const array<T, size> &a) {
  print(a[0]);
  for (auto i = a.begin(); ++i != a.end();) {
    putchar(' ');
    print(*i);
  }
}
template <class T, class L> void print(const pair<T, L> &p) {
  print(p.first);
  putchar(' ');
  print(p.second);
}
template <class T, size_t size> void print(const T (&a)[size]) {
  print(a[0]);
  for (auto i = a; ++i != end(a);) {
    putchar(' ');
    print(*i);
  }
}
template <class T> void print(const T &a) { cout << a; }
int out() {
  putchar('\\n');
  return 0;
}
template <class T> int out(const T &t) {
  print(t);
  putchar('\\n');
  return 0;
}
template <class Head, class... Tail>
int out(const Head &head, const Tail &...tail) {
  print(head);
  putchar(' ');
  out(tail...);
  return 0;
}
#ifdef DEBUG
inline ll __lg(ull __n) {
  return sizeof(ull) * __CHAR_BIT__ - 1 - __builtin_clzll(__n);
}
#define debug(...)                                                             \\
  {                                                                            \\
    print(#__VA_ARGS__);                                                       \\
    print(":");                                                                \\
    out(__VA_ARGS__);                                                          \\
  }
#else
#define debug(...) void(0)
#endif
int first(bool i = true) { return out(i ? "first" : "second"); }
int yes(bool i = true) { return out(i ? "yes" : "no"); }
int Yes(bool i = true) { return out(i ? "Yes" : "No"); }
int No() { return out("No"); }
int YES(bool i = true) { return out(i ? "YES" : "NO"); }
int NO() { return out("NO"); }
int Yay(bool i = true) { return out(i ? "Yay!" : ":("); }
int possible(bool i = true) { return out(i ? "possible" : "impossible"); }
int Possible(bool i = true) { return out(i ? "Possible" : "Impossible"); }
int POSSIBLE(bool i = true) { return out(i ? "POSSIBLE" : "IMPOSSIBLE"); }
void Case(ll i) { printf("Case #%lld: ", i); }

constexpr uint mod = MODD;
struct Modint {
  uint num = 0;
  constexpr Modint() noexcept {}
  constexpr Modint(const Modint &x) noexcept : num(x.num) {}
  inline constexpr operator ll() const noexcept { return num; }
  inline constexpr Modint &operator+=(Modint x) noexcept {
    num += x.num;
    if (num >= mod)
      num -= mod;
    return *this;
  }
  inline constexpr Modint &operator++() noexcept {
    if (num == mod - 1)
      num = 0;
    else
      num++;
    return *this;
  }
  inline constexpr Modint operator++(int) noexcept {
    Modint ans(*this);
    operator++();
    return ans;
  }
  inline constexpr Modint operator-() const noexcept {
    return Modint(0) -= *this;
  }
  inline constexpr Modint operator-(Modint x) const noexcept {
    return Modint(*this) -= x;
  }
  inline constexpr Modint &operator-=(Modint x) noexcept {
    if (num < x.num)
      num += mod;
    num -= x.num;
    return *this;
  }
  inline constexpr Modint &operator--() noexcept {
    if (num == 0)
      num = mod - 1;
    else
      num--;
    return *this;
  }
  inline constexpr Modint operator--(int) noexcept {
    Modint ans(*this);
    operator--();
    return ans;
  }
  inline constexpr Modint &operator*=(Modint x) noexcept {
    num = ull(num) * x.num % mod;
    return *this;
  }
  inline constexpr Modint &operator/=(Modint x) noexcept {
    return operator*=(x.inv());
  }
  template <class T> constexpr Modint(T x) noexcept {
    using U = typename conditional<sizeof(T) >= 4, T, int>::type;
    U y = x;
    y %= U(mod);
    if (y < 0)
      y += mod;
    num = uint(y);
  }
  template <class T> inline constexpr Modint operator+(T x) const noexcept {
    return Modint(*this) += x;
  }
  template <class T> inline constexpr Modint &operator+=(T x) noexcept {
    return operator+=(Modint(x));
  }
  template <class T> inline constexpr Modint operator-(T x) const noexcept {
    return Modint(*this) -= x;
  }
  template <class T> inline constexpr Modint &operator-=(T x) noexcept {
    return operator-=(Modint(x));
  }
  template <class T> inline constexpr Modint operator*(T x) const noexcept {
    return Modint(*this) *= x;
  }
  template <class T> inline constexpr Modint &operator*=(T x) noexcept {
    return operator*=(Modint(x));
  }
  template <class T> inline constexpr Modint operator/(T x) const noexcept {
    return Modint(*this) /= x;
  }
  template <class T> inline constexpr Modint &operator/=(T x) noexcept {
    return operator/=(Modint(x));
  }
  inline constexpr Modint inv() const noexcept {
    ll x = 0, y = 0;
    extgcd(num, mod, x, y);
    return x;
  }
  static inline constexpr ll extgcd(ll a, ll b, ll &x, ll &y) noexcept {
    ll g = a;
    x = 1;
    y = 0;
    if (b) {
      g = extgcd(b, a % b, y, x);
      y -= a / b * x;
    }
    return g;
  }
  inline constexpr Modint pow(ull x) const noexcept {
    Modint ans = 1, cnt = *this;
    while (x) {
      if (x & 1)
        ans *= cnt;
      cnt *= cnt;
      x /= 2;
    }
    return ans;
  }
};
std::istream &operator>>(std::istream &is, Modint &x) {
  ll a;
  in(a);
  x = a;
  return is;
}
inline constexpr Modint operator""_M(ull x) noexcept { return Modint(x); }
std::vector<Modint> fac(1, 1), inv(1, 1);
inline void reserve(ll a) {
  if (fac.size() >= a)
    return;
  if (a < fac.size() * 2)
    a = fac.size() * 2;
  if (a >= mod)
    a = mod;
  while (fac.size() < a)
    fac.push_back(fac.back() * Modint(fac.size()));
  inv.resize(fac.size());
  inv.back() = fac.back().inv();
  for (ll i = inv.size() - 1; !inv[i - 1]; i--)
    inv[i - 1] = inv[i] * i;
}
inline Modint fact(ll n) {
  if (n < 0)
    return 0;
  reserve(n + 1);
  return fac[n];
}
inline Modint perm(ll n, ll r) {
  if (r < 0 || n < r)
    return 0;
  if (n >> 24) {
    Modint ans = 1;
    for (ll i = 0; i < r; i++)
      ans *= n--;
    return ans;
  }
  reserve(n + 1);
  return fac[n] * inv[n - r];
}
inline Modint comb(ll n, ll r) {
  if (r < 0 || n < r)
    return 0;
  reserve(r + 1);
  return perm(n, r) * inv[r];
}
inline Modint Mcomb(ll n, ll r) {
  return comb(n + r - 1, n - 1);
} // r balls into n boxes
inline Modint catalan(ll n) {
  reserve(n * 2 + 1);
  return fac[n * 2] * inv[n] * inv[n + 1];
}
Modint mem[3001][3001];
ll a, b, c, d;
Modint dp(ll c, ll d) {
  if (mem[c][d].num != uint(-1))
    return mem[c][d];
  if (c < a || d < b)
    return 0;
  if (c == a && d == b)
    return mem[c][d] = 1;
  if (c == a)
    return mem[c][d] = dp(c, d - 1) * c;
  if (d == b)
    return mem[c][d] = dp(c - 1, d) * d;
  Modint ans = 0;
  ans += dp(c - 1, d - 1) * (c - 1) * (d - 1);
  Modint cnt = 1;
  rrep(i, a, c) {
    ans += dp(i, d - 1) * cnt * i;
    cnt *= d;
  }
  cnt = 1;
  rrep(i, b, d) {
    ans += dp(c - 1, i) * cnt * i;
    cnt *= c;
  }
  return mem[c][d] = ans;
}
signed main() {
  memset(mem, 0xff, sizeof(mem));
  in(a, b, c, d);
  out(dp(c, d));
}