Problem p02782 (C++)

Buggy submission (status: Runtime Error):
// >>> TEMPLATES
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define int ll
#define double ld
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep1(i, n) for (int i = 1; i <= (int)(n); i++)
#define repR(i, n) for (int i = (int)(n)-1; i >= 0; i--)
#define rep1R(i, n) for (int i = (int)(n); i >= 1; i--)
#define loop(i, a, B) for (int i = a; i B; i++)
#define loopR(i, a, B) for (int i = a; i B; i--)
#define all(x) (x).begin(), (x).end()
#define allR(x) (x).rbegin(), (x).rend()
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fst first
#define snd second
#define INF (numeric_limits<int>::max() / 2 - 1)
#ifdef LOCAL
#include "debug.hpp"
#define dump(...)                                                              \
  cerr << "[" << __LINE__ << ":" << __FUNCTION__ << "] ",                      \
      dump_impl(#__VA_ARGS__, __VA_ARGS__)
#define say(x)                                                                 \
  cerr << "[" << __LINE__ << ":" << __FUNCTION__ << "] " << x << endl
#define debug if (1)
#else
#define dump(...) (void)(0)
#define say(x) (void)(0)
#define debug if (0)
#endif
template <class T> using pque_max = priority_queue<T>;
template <class T> using pque_min = priority_queue<T, vector<T>, greater<T>>;
template <class T, class = typename T::iterator,
          class = typename enable_if<!is_same<T, string>::value>::type>
ostream &operator<<(ostream &os, T const &v) {
  bool f = true;
  for (auto const &x : v)
    os << (f ? "" : " ") << x, f = false;
  return os;
}
template <class T, class = typename T::iterator,
          class = typename enable_if<!is_same<T, string>::value>::type>
istream &operator>>(istream &is, T &v) {
  for (auto &x : v)
    is >> x;
  return is;
}
template <class T, class S> istream &operator>>(istream &is, pair<T, S> &p) {
  return is >> p.first >> p.second;
}
struct IOSetup {
  IOSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(15);
  }
} iosetup;
template <class F> struct FixPoint : private F {
  constexpr FixPoint(F &&f) : F(forward<F>(f)) {}
  template <class... T> constexpr auto operator()(T &&...x) const {
    return F::operator()(*this, forward<T>(x)...);
  }
};
struct MakeFixPoint {
  template <class F> constexpr auto operator|(F &&f) const {
    return FixPoint<F>(forward<F>(f));
  }
};
#define MFP MakeFixPoint() |
#define def(name, ...) auto name = MFP[&](auto &&name, __VA_ARGS__)
template <class T, size_t d> struct vec_impl {
  using type = vector<typename vec_impl<T, d - 1>::type>;
  template <class... U> static type make_v(size_t n, U &&...x) {
    return type(n, vec_impl<T, d - 1>::make_v(forward<U>(x)...));
  }
};
template <class T> struct vec_impl<T, 0> {
  using type = T;
  static type make_v(T const &x = {}) { return x; }
};
template <class T, size_t d = 1> using vec = typename vec_impl<T, d>::type;
template <class T, size_t d = 1, class... Args> auto make_v(Args &&...args) {
  return vec_impl<T, d>::make_v(forward<Args>(args)...);
}
template <class T> void quit(T const &x) {
  cout << x << endl;
  exit(0);
}
template <class T> constexpr bool chmin(T &x, T const &y) {
  if (x > y) {
    x = y;
    return true;
  }
  return false;
}
template <class T> constexpr bool chmax(T &x, T const &y) {
  if (x < y) {
    x = y;
    return true;
  }
  return false;
}
template <class It> constexpr auto sumof(It b, It e) {
  return accumulate(b, e, typename iterator_traits<It>::value_type{});
}
template <class T> int sz(T const &x) { return x.size(); }
template <class C, class T> int lbd(C const &v, T const &x) {
  return lower_bound(v.begin(), v.end(), x) - v.begin();
}
template <class C, class T> int ubd(C const &v, T const &x) {
  return upper_bound(v.begin(), v.end(), x) - v.begin();
}
// <<<
// >>> modint
template <int32_t md> class modint {
  static_assert(md > 0, "");
  using M = modint;
  using ll = int64_t;
  int32_t x;

public:
  static constexpr int32_t mod = md;
  constexpr modint(ll x = 0) : x((x %= mod) < 0 ? x + mod : x) {}
  constexpr ll val() const { return x; }
  constexpr operator ll() const { return x; }
  constexpr bool operator==(M const &r) const { return x == r.x; }
  constexpr bool operator!=(M const &r) const { return x != r.x; }
  constexpr M operator+() const { return *this; }
  constexpr M operator-() const { return M() - *this; }
  constexpr M &operator+=(M const &r) {
    ll t = ll(x) + r.x;
    if (t >= mod)
      t -= mod;
    x = t;
    return *this;
  }
  constexpr M &operator-=(M const &r) {
    ll t = ll(x) + mod - r.x;
    if (t >= mod)
      t -= mod;
    x = t;
    return *this;
  }
  constexpr M &operator*=(M const &r) { return *this = *this * r; }
  constexpr M operator*(M const &r) const {
    M t;
    t.x = (ll(x) * r.x) % mod;
    return t;
  }
  constexpr M &operator/=(M const &r) { return *this *= r.inv(); }
  constexpr M operator+(M const &r) const { return M(*this) += r; }
  constexpr M operator-(M const &r) const { return M(*this) -= r; }
  constexpr M operator/(M const &r) const { return M(*this) /= r; }
  friend constexpr M operator+(ll x, M const &y) { return M(x) + y; }
  friend constexpr M operator-(ll x, M const &y) { return M(x) - y; }
  friend constexpr M operator*(ll x, M const &y) { return M(x) * y; }
  friend constexpr M operator/(ll x, M const &y) { return M(x) / y; }
  constexpr M pow(ll n) const {
    if (n < 0)
      return inv().pow(-n);
    M v = *this, r = 1;
    for (; n > 0; n >>= 1, v *= v)
      if (n & 1)
        r *= v;
    return r;
  }
  constexpr M inv() const {
    assert(x > 0);
    ll t = 1, v = x, q = 0, r = 0;
    while (v != 1) {
      q = mod / v;
      r = mod % v;
      if (r * 2 < v) {
        t *= -q;
        t %= mod;
        v = r;
      } else {
        t *= q + 1;
        t %= mod;
        v -= r;
      }
    }
    if (t < 0)
      t += mod;
    M y;
    y.x = t;
    return y;
  }
#ifdef LOCAL
  friend string to_s(M r) { return to_s(r.val(), mod); }
#endif
  friend ostream &operator<<(ostream &os, M r) { return os << r.val(); }
  friend istream &operator>>(istream &is, M &r) {
    int64_t x;
    is >> x;
    r = x;
    return is;
  }
};
// <<<
// constexpr int64_t MOD = 998244353;
constexpr int64_t MOD = 1e9 + 7;
using mint = modint<(int32_t)MOD>;

// >>> mod table
template <int32_t mod> struct ModTable {
  static constexpr int32_t Size = 1e6 + 10;
  static_assert(Size <= mod, "");
  using ll = int64_t;
  int32_t fact[Size], finv[Size], inv[Size];
  ModTable() {
    fact[0] = fact[1] = finv[0] = finv[1] = inv[1] = 1;
    for (int i = 2; i < Size; i++) {
      fact[i] = ll(fact[i - 1]) * i % mod;
      inv[i] = mod - ll(inv[mod % i]) * (mod / i) % mod;
      finv[i] = ll(finv[i - 1]) * inv[i] % mod;
    }
  }
};
const ModTable<MOD> mod_tab;

modint<MOD> fact(int n) {
  assert(0 <= n);
  assert(n < ModTable<MOD>::Size);
  return mod_tab.fact[n];
}
modint<MOD> finv(int n) {
  assert(0 <= n);
  assert(n < ModTable<MOD>::Size);
  return mod_tab.finv[n];
}
modint<MOD> C(int n, int k) {
  if (n < 0 || k < 0 || n < k)
    return 0;
  return fact(n) * finv(k) * finv(n - k);
}
modint<MOD> P(int n, int k) {
  assert(k >= 0);
  return fact(n) * finv(n - k);
}
// <<<

int32_t main() {
  int r1, c1, r2, c2;
  cin >> r1 >> c1 >> r2 >> c2;

  auto f = [&](int n, int k) { return C(n + k + 1, k); };
  mint sum = 0;
  loop(i, r1, <= r2) sum += f(i, c2) - f(i, c1 - 1);
  cout << sum << endl;
}


Fixed submission:
// >>> TEMPLATES
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define int ll
#define double ld
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep1(i, n) for (int i = 1; i <= (int)(n); i++)
#define repR(i, n) for (int i = (int)(n)-1; i >= 0; i--)
#define rep1R(i, n) for (int i = (int)(n); i >= 1; i--)
#define loop(i, a, B) for (int i = a; i B; i++)
#define loopR(i, a, B) for (int i = a; i B; i--)
#define all(x) (x).begin(), (x).end()
#define allR(x) (x).rbegin(), (x).rend()
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fst first
#define snd second
#define INF (numeric_limits<int>::max() / 2 - 1)
#ifdef LOCAL
#include "debug.hpp"
#define dump(...)                                                              \
  cerr << "[" << __LINE__ << ":" << __FUNCTION__ << "] ",                      \
      dump_impl(#__VA_ARGS__, __VA_ARGS__)
#define say(x)                                                                 \
  cerr << "[" << __LINE__ << ":" << __FUNCTION__ << "] " << x << endl
#define debug if (1)
#else
#define dump(...) (void)(0)
#define say(x) (void)(0)
#define debug if (0)
#endif
template <class T> using pque_max = priority_queue<T>;
template <class T> using pque_min = priority_queue<T, vector<T>, greater<T>>;
template <class T, class = typename T::iterator,
          class = typename enable_if<!is_same<T, string>::value>::type>
ostream &operator<<(ostream &os, T const &v) {
  bool f = true;
  for (auto const &x : v)
    os << (f ? "" : " ") << x, f = false;
  return os;
}
template <class T, class = typename T::iterator,
          class = typename enable_if<!is_same<T, string>::value>::type>
istream &operator>>(istream &is, T &v) {
  for (auto &x : v)
    is >> x;
  return is;
}
template <class T, class S> istream &operator>>(istream &is, pair<T, S> &p) {
  return is >> p.first >> p.second;
}
struct IOSetup {
  IOSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(15);
  }
} iosetup;
template <class F> struct FixPoint : private F {
  constexpr FixPoint(F &&f) : F(forward<F>(f)) {}
  template <class... T> constexpr auto operator()(T &&...x) const {
    return F::operator()(*this, forward<T>(x)...);
  }
};
struct MakeFixPoint {
  template <class F> constexpr auto operator|(F &&f) const {
    return FixPoint<F>(forward<F>(f));
  }
};
#define MFP MakeFixPoint() |
#define def(name, ...) auto name = MFP[&](auto &&name, __VA_ARGS__)
template <class T, size_t d> struct vec_impl {
  using type = vector<typename vec_impl<T, d - 1>::type>;
  template <class... U> static type make_v(size_t n, U &&...x) {
    return type(n, vec_impl<T, d - 1>::make_v(forward<U>(x)...));
  }
};
template <class T> struct vec_impl<T, 0> {
  using type = T;
  static type make_v(T const &x = {}) { return x; }
};
template <class T, size_t d = 1> using vec = typename vec_impl<T, d>::type;
template <class T, size_t d = 1, class... Args> auto make_v(Args &&...args) {
  return vec_impl<T, d>::make_v(forward<Args>(args)...);
}
template <class T> void quit(T const &x) {
  cout << x << endl;
  exit(0);
}
template <class T> constexpr bool chmin(T &x, T const &y) {
  if (x > y) {
    x = y;
    return true;
  }
  return false;
}
template <class T> constexpr bool chmax(T &x, T const &y) {
  if (x < y) {
    x = y;
    return true;
  }
  return false;
}
template <class It> constexpr auto sumof(It b, It e) {
  return accumulate(b, e, typename iterator_traits<It>::value_type{});
}
template <class T> int sz(T const &x) { return x.size(); }
template <class C, class T> int lbd(C const &v, T const &x) {
  return lower_bound(v.begin(), v.end(), x) - v.begin();
}
template <class C, class T> int ubd(C const &v, T const &x) {
  return upper_bound(v.begin(), v.end(), x) - v.begin();
}
// <<<
// >>> modint
template <int32_t md> class modint {
  static_assert(md > 0, "");
  using M = modint;
  using ll = int64_t;
  int32_t x;

public:
  static constexpr int32_t mod = md;
  constexpr modint(ll x = 0) : x((x %= mod) < 0 ? x + mod : x) {}
  constexpr ll val() const { return x; }
  constexpr operator ll() const { return x; }
  constexpr bool operator==(M const &r) const { return x == r.x; }
  constexpr bool operator!=(M const &r) const { return x != r.x; }
  constexpr M operator+() const { return *this; }
  constexpr M operator-() const { return M() - *this; }
  constexpr M &operator+=(M const &r) {
    ll t = ll(x) + r.x;
    if (t >= mod)
      t -= mod;
    x = t;
    return *this;
  }
  constexpr M &operator-=(M const &r) {
    ll t = ll(x) + mod - r.x;
    if (t >= mod)
      t -= mod;
    x = t;
    return *this;
  }
  constexpr M &operator*=(M const &r) { return *this = *this * r; }
  constexpr M operator*(M const &r) const {
    M t;
    t.x = (ll(x) * r.x) % mod;
    return t;
  }
  constexpr M &operator/=(M const &r) { return *this *= r.inv(); }
  constexpr M operator+(M const &r) const { return M(*this) += r; }
  constexpr M operator-(M const &r) const { return M(*this) -= r; }
  constexpr M operator/(M const &r) const { return M(*this) /= r; }
  friend constexpr M operator+(ll x, M const &y) { return M(x) + y; }
  friend constexpr M operator-(ll x, M const &y) { return M(x) - y; }
  friend constexpr M operator*(ll x, M const &y) { return M(x) * y; }
  friend constexpr M operator/(ll x, M const &y) { return M(x) / y; }
  constexpr M pow(ll n) const {
    if (n < 0)
      return inv().pow(-n);
    M v = *this, r = 1;
    for (; n > 0; n >>= 1, v *= v)
      if (n & 1)
        r *= v;
    return r;
  }
  constexpr M inv() const {
    assert(x > 0);
    ll t = 1, v = x, q = 0, r = 0;
    while (v != 1) {
      q = mod / v;
      r = mod % v;
      if (r * 2 < v) {
        t *= -q;
        t %= mod;
        v = r;
      } else {
        t *= q + 1;
        t %= mod;
        v -= r;
      }
    }
    if (t < 0)
      t += mod;
    M y;
    y.x = t;
    return y;
  }
#ifdef LOCAL
  friend string to_s(M r) { return to_s(r.val(), mod); }
#endif
  friend ostream &operator<<(ostream &os, M r) { return os << r.val(); }
  friend istream &operator>>(istream &is, M &r) {
    int64_t x;
    is >> x;
    r = x;
    return is;
  }
};
// <<<
// constexpr int64_t MOD = 998244353;
constexpr int64_t MOD = 1e9 + 7;
using mint = modint<(int32_t)MOD>;

// >>> mod table
template <int32_t mod> struct ModTable {
  static constexpr int32_t Size = 3e6 + 10;
  static_assert(Size <= mod, "");
  using ll = int64_t;
  int32_t fact[Size], finv[Size], inv[Size];
  ModTable() {
    fact[0] = fact[1] = finv[0] = finv[1] = inv[1] = 1;
    for (int i = 2; i < Size; i++) {
      fact[i] = ll(fact[i - 1]) * i % mod;
      inv[i] = mod - ll(inv[mod % i]) * (mod / i) % mod;
      finv[i] = ll(finv[i - 1]) * inv[i] % mod;
    }
  }
};
const ModTable<MOD> mod_tab;

modint<MOD> fact(int n) {
  assert(0 <= n);
  assert(n < ModTable<MOD>::Size);
  return mod_tab.fact[n];
}
modint<MOD> finv(int n) {
  assert(0 <= n);
  assert(n < ModTable<MOD>::Size);
  return mod_tab.finv[n];
}
modint<MOD> C(int n, int k) {
  if (n < 0 || k < 0 || n < k)
    return 0;
  return fact(n) * finv(k) * finv(n - k);
}
modint<MOD> P(int n, int k) {
  assert(k >= 0);
  return fact(n) * finv(n - k);
}
// <<<

int32_t main() {
  int r1, c1, r2, c2;
  cin >> r1 >> c1 >> r2 >> c2;

  auto f = [&](int n, int k) { return C(n + k + 1, k); };
  mint sum = 0;
  loop(i, r1, <= r2) sum += f(i, c2) - f(i, c1 - 1);
  cout << sum << endl;
}