Problem p02782 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vb = vector<bool>;
using vvb = vector<vb>;
using vd = vector<double>;
using vvd = vector<vd>;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using pll = pair<ll, ll>;
using tll = tuple<ll, ll>;
using tlll = tuple<ll, ll, ll>;
using vs = vector<string>;
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define rep(i, n) range(i, 0, n)
#define rrep(i, n) for (ll i = (n)-1; i >= 0; i--)
#define range(i, a, n) for (ll i = (a); i < (n); i++)
#define LINF ((ll)1ll << 60)
#define INF ((int)1 << 30)
#define EPS (1e-9)
#define MOD (1000000007ll)
#define fcout(a) cout << setprecision(a) << fixed
#define fs first
#define sc second
#define PI (3.1415926535897932384)

int dx[] = {1, 0, -1, 0, 1, -1, -1, 1}, dy[] = {0, 1, 0, -1, 1, 1, -1, -1};
template <class T> bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class S> S sum(vector<S> &a) { return accumulate(all(a), S()); }
template <class S> S max(vector<S> &a) { return *max_element(all(a)); }
template <class S> S min(vector<S> &a) { return *min_element(all(a)); }
ll max(int a, ll b) { return max((ll)a, b); }
ll max(ll a, int b) { return max(a, (ll)b); }
int sgn(const double &r) { return (r > EPS) - (r < -EPS); } // a>0  : sgn(a)>0
int sgn(const double &a, const double &b) {
  return sgn(a - b);
} // b<=c : sgn(b,c)<=0

template <class T> void puta(T &&t) { cout << t << "\n"; }
template <class H, class... T> void puta(H &&h, T &&...t) {
  cout << h << ' ';
  puta(t...);
}
template <class S, class T> void tf(bool b, S t, T f) {
  if (b)
    puta(t);
  else
    puta(f);
}
void YN(bool b) { tf(b, "YES", "NO"); }
void Yn(bool b) { tf(b, "Yes", "No"); }
void yn(bool b) { tf(b, "yes", "no"); }
template <class S, class T> ostream &operator<<(ostream &os, pair<S, T> p) {
  os << "[" << p.first << ", " << p.second << "]";
  return os;
};
template <class S> auto &operator<<(ostream &os, vector<S> t) {
  bool a = 1;
  for (auto s : t) {
    os << (a ? "" : " ") << s;
    a = 0;
  }
  return os;
}
template <class S> auto &operator>>(istream &is, vector<S> &t) {
  for (S &a : t)
    cin >> a;
  return is;
}

/*他のライブラリを入れる場所*/
template <int _MOD> struct modint {
  ll val;
  constexpr static int setModMax = 510000;
  static modint<_MOD> fac[setModMax], finv[setModMax], inv[setModMax];

  static constexpr ll mod(ll a) { return (a % _MOD + _MOD) % _MOD; }
  constexpr modint(ll v = 0) noexcept : val(v % _MOD) {
    if (val < 0)
      v += _MOD;
  }
  constexpr int getmod() { return _MOD; }
  constexpr modint operator-() const noexcept { return val ? _MOD - val : 0; }
  constexpr modint operator+(const modint &r) const noexcept {
    return modint(*this) += r;
  }
  constexpr modint operator-(const modint &r) const noexcept {
    return modint(*this) -= r;
  }
  constexpr modint operator*(const modint &r) const noexcept {
    return modint(*this) *= r;
  }
  constexpr modint operator/(const modint &r) const noexcept {
    return modint(*this) /= r;
  }
  constexpr modint operator^(const modint &r) const noexcept {
    return modint(*this) ^= r;
  }
  constexpr modint &operator+=(const modint &r) noexcept {
    val = mod(val + r.val);
    return *this;
  }
  constexpr modint &operator-=(const modint &r) noexcept {
    val = mod(val - r.val);
    return *this;
  }
  constexpr modint &operator*=(const modint &r) noexcept {
    val = mod(val * r.val);
    return *this;
  }
  constexpr modint &operator/=(const modint &r) noexcept {
    ll a = r.val, b = _MOD, u = 1, v = 0;
    while (b) {
      ll t = a / b;
      a -= t * b;
      swap(a, b);
      u -= t * v;
      swap(u, v);
    }
    val = val * u % _MOD;
    if (val < 0)
      val += _MOD;
    return *this;
  }
  constexpr modint &operator^=(const modint &r) noexcept {
    val = modpow(val, r.val).val;
    return *this;
  }
  constexpr bool operator<(const modint &r) const noexcept {
    return this->val < r.val;
  }
  constexpr bool operator>(const modint &r) const noexcept { return r < *this; }
  constexpr bool operator!=(const modint &r) const noexcept {
    return *this < r || *this > r;
  }
  constexpr bool operator==(const modint &r) const noexcept {
    return !(*this != r);
  }
  constexpr bool operator<=(const modint &r) const noexcept {
    return !(*this > r);
  }
  constexpr bool operator>=(const modint &r) const noexcept {
    return !(*this < r);
  }
  friend constexpr ostream &operator<<(ostream &os,
                                       const modint<_MOD> &x) noexcept {
    return os << x.val;
  }
  friend constexpr istream &operator>>(istream &is, modint<_MOD> &x) noexcept {
    return is >> x.val;
  }
  constexpr modint<_MOD> modpow(const modint<_MOD> &a, ll n) noexcept {
    if (n == 0)
      return 1;
    auto t = modpow(a, n / 2);
    t *= t;
    if (n & 1)
      t *= a;
    return t;
  }
  friend modint<_MOD> operator+(const ll a, const modint &b) {
    return modint(a) += b;
  }
  friend void operator+=(ll &a, const modint &b) { a = modint(a) + b; }
  friend modint<_MOD> operator-(const ll a, const modint &b) {
    return modint(a) -= b;
  }
  friend void operator-=(ll &a, const modint &b) { a = modint(a) - b; }
  friend modint<_MOD> operator*(const ll a, const modint &b) {
    return modint(a) *= b;
  }
  friend void operator*=(ll &a, const modint &b) { a = modint(a) * b; }
  friend modint<_MOD> operator/(const ll a, const modint &b) {
    return modint(a) /= b;
  }
  friend void operator/=(ll &a, const modint &b) { a = modint(a) / b; }
  friend modint<_MOD> operator^(const ll a, const modint &b) {
    return modint(a) ^= b;
  }
  friend void operator^=(ll &a, const modint &b) { a = modint(a) ^ b; }
};
using mint = modint<MOD>;
using vm = vector<mint>;
using vvm = vector<vm>;
mint operator""_m(unsigned long long a) { return mint(a); }
mint nCr(ll n, ll r) {
  const static int setModMax = 1010000;
  static mint fac[setModMax], finv[setModMax], inv[setModMax];
  if (fac[0] == 0) {
    fac[0] = fac[1] = finv[0] = finv[1] = inv[1] = 1;
    for (int i = 2; i < setModMax; i++) {
      fac[i] = fac[i - 1] * i;
      inv[i] = -inv[MOD % i] * (MOD / i);
      finv[i] = finv[i - 1] * inv[i];
    }
  }
  return fac[n] * finv[r] * finv[n - r];
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  ll a, b, c, d;
  cin >> a >> c >> b >> d;
  mint ans = 0;
  range(i, a, b + 1) {
    ans += nCr(i + 1 + d, i + 1) - nCr(i + 1 + c - 1, i + 1);
  }
  puta(ans);
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vb = vector<bool>;
using vvb = vector<vb>;
using vd = vector<double>;
using vvd = vector<vd>;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using pll = pair<ll, ll>;
using tll = tuple<ll, ll>;
using tlll = tuple<ll, ll, ll>;
using vs = vector<string>;
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define rep(i, n) range(i, 0, n)
#define rrep(i, n) for (ll i = (n)-1; i >= 0; i--)
#define range(i, a, n) for (ll i = (a); i < (n); i++)
#define LINF ((ll)1ll << 60)
#define INF ((int)1 << 30)
#define EPS (1e-9)
#define MOD (1000000007ll)
#define fcout(a) cout << setprecision(a) << fixed
#define fs first
#define sc second
#define PI (3.1415926535897932384)

int dx[] = {1, 0, -1, 0, 1, -1, -1, 1}, dy[] = {0, 1, 0, -1, 1, 1, -1, -1};
template <class T> bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class S> S sum(vector<S> &a) { return accumulate(all(a), S()); }
template <class S> S max(vector<S> &a) { return *max_element(all(a)); }
template <class S> S min(vector<S> &a) { return *min_element(all(a)); }
ll max(int a, ll b) { return max((ll)a, b); }
ll max(ll a, int b) { return max(a, (ll)b); }
int sgn(const double &r) { return (r > EPS) - (r < -EPS); } // a>0  : sgn(a)>0
int sgn(const double &a, const double &b) {
  return sgn(a - b);
} // b<=c : sgn(b,c)<=0

template <class T> void puta(T &&t) { cout << t << "\n"; }
template <class H, class... T> void puta(H &&h, T &&...t) {
  cout << h << ' ';
  puta(t...);
}
template <class S, class T> void tf(bool b, S t, T f) {
  if (b)
    puta(t);
  else
    puta(f);
}
void YN(bool b) { tf(b, "YES", "NO"); }
void Yn(bool b) { tf(b, "Yes", "No"); }
void yn(bool b) { tf(b, "yes", "no"); }
template <class S, class T> ostream &operator<<(ostream &os, pair<S, T> p) {
  os << "[" << p.first << ", " << p.second << "]";
  return os;
};
template <class S> auto &operator<<(ostream &os, vector<S> t) {
  bool a = 1;
  for (auto s : t) {
    os << (a ? "" : " ") << s;
    a = 0;
  }
  return os;
}
template <class S> auto &operator>>(istream &is, vector<S> &t) {
  for (S &a : t)
    cin >> a;
  return is;
}

/*他のライブラリを入れる場所*/
template <int _MOD> struct modint {
  ll val;
  constexpr static int setModMax = 510000;
  static modint<_MOD> fac[setModMax], finv[setModMax], inv[setModMax];

  static constexpr ll mod(ll a) { return (a % _MOD + _MOD) % _MOD; }
  constexpr modint(ll v = 0) noexcept : val(v % _MOD) {
    if (val < 0)
      v += _MOD;
  }
  constexpr int getmod() { return _MOD; }
  constexpr modint operator-() const noexcept { return val ? _MOD - val : 0; }
  constexpr modint operator+(const modint &r) const noexcept {
    return modint(*this) += r;
  }
  constexpr modint operator-(const modint &r) const noexcept {
    return modint(*this) -= r;
  }
  constexpr modint operator*(const modint &r) const noexcept {
    return modint(*this) *= r;
  }
  constexpr modint operator/(const modint &r) const noexcept {
    return modint(*this) /= r;
  }
  constexpr modint operator^(const modint &r) const noexcept {
    return modint(*this) ^= r;
  }
  constexpr modint &operator+=(const modint &r) noexcept {
    val = mod(val + r.val);
    return *this;
  }
  constexpr modint &operator-=(const modint &r) noexcept {
    val = mod(val - r.val);
    return *this;
  }
  constexpr modint &operator*=(const modint &r) noexcept {
    val = mod(val * r.val);
    return *this;
  }
  constexpr modint &operator/=(const modint &r) noexcept {
    ll a = r.val, b = _MOD, u = 1, v = 0;
    while (b) {
      ll t = a / b;
      a -= t * b;
      swap(a, b);
      u -= t * v;
      swap(u, v);
    }
    val = val * u % _MOD;
    if (val < 0)
      val += _MOD;
    return *this;
  }
  constexpr modint &operator^=(const modint &r) noexcept {
    val = modpow(val, r.val).val;
    return *this;
  }
  constexpr bool operator<(const modint &r) const noexcept {
    return this->val < r.val;
  }
  constexpr bool operator>(const modint &r) const noexcept { return r < *this; }
  constexpr bool operator!=(const modint &r) const noexcept {
    return *this < r || *this > r;
  }
  constexpr bool operator==(const modint &r) const noexcept {
    return !(*this != r);
  }
  constexpr bool operator<=(const modint &r) const noexcept {
    return !(*this > r);
  }
  constexpr bool operator>=(const modint &r) const noexcept {
    return !(*this < r);
  }
  friend constexpr ostream &operator<<(ostream &os,
                                       const modint<_MOD> &x) noexcept {
    return os << x.val;
  }
  friend constexpr istream &operator>>(istream &is, modint<_MOD> &x) noexcept {
    return is >> x.val;
  }
  constexpr modint<_MOD> modpow(const modint<_MOD> &a, ll n) noexcept {
    if (n == 0)
      return 1;
    auto t = modpow(a, n / 2);
    t *= t;
    if (n & 1)
      t *= a;
    return t;
  }
  friend modint<_MOD> operator+(const ll a, const modint &b) {
    return modint(a) += b;
  }
  friend void operator+=(ll &a, const modint &b) { a = modint(a) + b; }
  friend modint<_MOD> operator-(const ll a, const modint &b) {
    return modint(a) -= b;
  }
  friend void operator-=(ll &a, const modint &b) { a = modint(a) - b; }
  friend modint<_MOD> operator*(const ll a, const modint &b) {
    return modint(a) *= b;
  }
  friend void operator*=(ll &a, const modint &b) { a = modint(a) * b; }
  friend modint<_MOD> operator/(const ll a, const modint &b) {
    return modint(a) /= b;
  }
  friend void operator/=(ll &a, const modint &b) { a = modint(a) / b; }
  friend modint<_MOD> operator^(const ll a, const modint &b) {
    return modint(a) ^= b;
  }
  friend void operator^=(ll &a, const modint &b) { a = modint(a) ^ b; }
};
using mint = modint<MOD>;
using vm = vector<mint>;
using vvm = vector<vm>;
mint operator""_m(unsigned long long a) { return mint(a); }
mint nCr(ll n, ll r) {
  const static int setModMax = 2010000;
  static mint fac[setModMax], finv[setModMax], inv[setModMax];
  if (fac[0] == 0) {
    fac[0] = fac[1] = finv[0] = finv[1] = inv[1] = 1;
    for (int i = 2; i < setModMax; i++) {
      fac[i] = fac[i - 1] * i;
      inv[i] = -inv[MOD % i] * (MOD / i);
      finv[i] = finv[i - 1] * inv[i];
    }
  }
  return fac[n] * finv[r] * finv[n - r];
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  ll a, b, c, d;
  cin >> a >> c >> b >> d;
  mint ans = 0;
  range(i, a, b + 1) {
    ans += nCr(i + 1 + d, i + 1) - nCr(i + 1 + c - 1, i + 1);
  }
  puta(ans);
  return 0;
}