Problem p02782 (C++)

Buggy submission (status: Runtime Error):
// #define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define rep(i, n) for (int i = 0; i < n; ++i)
#define REP(i, n) for (int i = 0; i < n; ++i)
#define range(i, a, b) ((a) <= (i) && (i) < (b))
#define debug(x) cout << #x << ' ' << '=' << ' ' << (x) << endl;
#define fs first
#define sc second
#define pb push_back
typedef long long ll;
typedef pair<ll, ll> P;
typedef tuple<ll, ll, ll> T;
typedef priority_queue<ll> PQI;
typedef priority_queue<P> PQP;
typedef vector<vector<P>> pvec;
typedef vector<vector<ll>> vvec;
typedef vector<ll> vec;
const vector<int> dx = {0, -1, 0, 1, 1, 1, -1, -1};
const vector<int> dy = {1, 0, -1, 0, 1, -1, 1, -1};
const int MOD = (1000000007);
// const int MOD = (998244353);
// const int INF = (1 << 30);
const int INF = (1LL << 60);
const double EPS = (1 >> 30);
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}

#include <cstdint>

template <long long Modulus> class modint {
  long long a;

public:
  constexpr modint(const long long x = 0) noexcept
      : a((x % Modulus + Modulus) % Modulus) {}
  constexpr long long val() const noexcept { return a; }
  constexpr modint operator+(const modint rhs) const noexcept {
    return modint(*this) += rhs;
  }
  constexpr modint operator-(const modint rhs) const noexcept {
    return modint(*this) -= rhs;
  }
  constexpr modint operator*(const modint rhs) const noexcept {
    return modint(*this) *= rhs;
  }
  constexpr modint operator/(const modint rhs) const noexcept {
    return modint(*this) /= rhs;
  }
  constexpr modint &operator+=(const modint rhs) noexcept {
    a += rhs.a;
    if (a >= Modulus) {
      a -= Modulus;
    }
    return *this;
  }
  constexpr modint &operator-=(const modint rhs) noexcept {
    if (a < rhs.a) {
      a += Modulus;
    }
    a -= rhs.a;
    return *this;
  }
  constexpr modint &operator*=(const modint rhs) noexcept {
    a = a * rhs.a % Modulus;
    return *this;
  }
  constexpr modint &operator/=(modint rhs) noexcept {
    long long exp = Modulus - 2;
    while (exp) {
      if (exp % 2) {
        *this *= rhs;
      }
      rhs *= rhs;
      exp /= 2;
    }
    return *this;
  }
  constexpr bool operator==(const modint rhs) const noexcept {
    return modint(*this).val() == rhs.val();
  }
  constexpr bool operator!=(const modint rhs) const noexcept {
    return modint(*this).val() != rhs.val();
  }
};
using mint = modint<MOD>;
typedef vector<mint> mvec;
typedef vector<vector<mint>> mvvec;

// 二項係数ライブラリ
template <class T> struct BC {
  vector<T> fact_, inv_, finv_;
  constexpr BC() {}
  constexpr BC(int n) noexcept : fact_(n, 1), inv_(n, 1), finv_(n, 1) {
    init(n);
  }
  constexpr void init(int n) noexcept {
    fact_.assign(n, 1);
    inv_.assign(n, 1);
    finv_.assign(n, 1);
    for (int i = 2; i < n; i++) {
      fact_[i] = fact_[i - 1] * i;
      inv_[i] = inv_[MOD % i] * (MOD / i) * (-1);
      finv_[i] = finv_[i - 1] * inv_[i];
    }
  }
  constexpr T nCr(int n, int k) const noexcept {
    if (n < k || n < 0 || k < 0)
      return 0;
    return fact_[n] * finv_[k] * finv_[n - k];
  }
  constexpr T nPr(int n, int k) const noexcept {
    if (n < k || n < 0 || k < 0)
      return 0;
    return fact_[n] * finv_[n - k];
  }
  constexpr T nHr(int n, int k) const noexcept { return nCr(n + k - 1, k); }
  constexpr T fact(int n) const noexcept {
    if (n < 0)
      return 0;
    return fact_[n];
  }
  constexpr T inv(int n) const noexcept {
    if (n < 0)
      return 0;
    return inv_[n];
  }
  constexpr T finv(int n) const noexcept {
    if (n < 0)
      return 0;
    return finv_[n];
  }
};

signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(15);
  //---------------------------------------------

  int a, b, c, d;

  BC<mint> bc(1000000 + 10);
  cin >> a >> b >> c >> d;
  mint ans = 0;
  for (int i = a + 1; i <= c; i++) {
    ans += bc.fact(i + d) * bc.finv(i) * bc.finv(d);
  }
  for (int i = b + 1; i <= d; i++) {
    ans += bc.fact(i + c) * bc.finv(i) * bc.finv(c);
  }
  ans += bc.fact(a + b) * bc.finv(a) * bc.finv(b);
  cout << ans.val() << endl;
}

Fixed submission:
// #define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define rep(i, n) for (int i = 0; i < n; ++i)
#define REP(i, n) for (int i = 0; i < n; ++i)
#define range(i, a, b) ((a) <= (i) && (i) < (b))
#define debug(x) cout << #x << ' ' << '=' << ' ' << (x) << endl;
#define fs first
#define sc second
#define pb push_back
typedef long long ll;
typedef pair<ll, ll> P;
typedef tuple<ll, ll, ll> T;
typedef priority_queue<ll> PQI;
typedef priority_queue<P> PQP;
typedef vector<vector<P>> pvec;
typedef vector<vector<ll>> vvec;
typedef vector<ll> vec;
const vector<int> dx = {0, -1, 0, 1, 1, 1, -1, -1};
const vector<int> dy = {1, 0, -1, 0, 1, -1, 1, -1};
const int MOD = (1000000007);
// const int MOD = (998244353);
// const int INF = (1 << 30);
const int INF = (1LL << 60);
const double EPS = (1 >> 30);
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}

#include <cstdint>

template <long long Modulus> class modint {
  long long a;

public:
  constexpr modint(const long long x = 0) noexcept
      : a((x % Modulus + Modulus) % Modulus) {}
  constexpr long long val() const noexcept { return a; }
  constexpr modint operator+(const modint rhs) const noexcept {
    return modint(*this) += rhs;
  }
  constexpr modint operator-(const modint rhs) const noexcept {
    return modint(*this) -= rhs;
  }
  constexpr modint operator*(const modint rhs) const noexcept {
    return modint(*this) *= rhs;
  }
  constexpr modint operator/(const modint rhs) const noexcept {
    return modint(*this) /= rhs;
  }
  constexpr modint &operator+=(const modint rhs) noexcept {
    a += rhs.a;
    if (a >= Modulus) {
      a -= Modulus;
    }
    return *this;
  }
  constexpr modint &operator-=(const modint rhs) noexcept {
    if (a < rhs.a) {
      a += Modulus;
    }
    a -= rhs.a;
    return *this;
  }
  constexpr modint &operator*=(const modint rhs) noexcept {
    a = a * rhs.a % Modulus;
    return *this;
  }
  constexpr modint &operator/=(modint rhs) noexcept {
    long long exp = Modulus - 2;
    while (exp) {
      if (exp % 2) {
        *this *= rhs;
      }
      rhs *= rhs;
      exp /= 2;
    }
    return *this;
  }
  constexpr bool operator==(const modint rhs) const noexcept {
    return modint(*this).val() == rhs.val();
  }
  constexpr bool operator!=(const modint rhs) const noexcept {
    return modint(*this).val() != rhs.val();
  }
};
using mint = modint<MOD>;
typedef vector<mint> mvec;
typedef vector<vector<mint>> mvvec;

// 二項係数ライブラリ
template <class T> struct BC {
  vector<T> fact_, inv_, finv_;
  constexpr BC() {}
  constexpr BC(int n) noexcept : fact_(n, 1), inv_(n, 1), finv_(n, 1) {
    init(n);
  }
  constexpr void init(int n) noexcept {
    fact_.assign(n, 1);
    inv_.assign(n, 1);
    finv_.assign(n, 1);
    for (int i = 2; i < n; i++) {
      fact_[i] = fact_[i - 1] * i;
      inv_[i] = inv_[MOD % i] * (MOD / i) * (-1);
      finv_[i] = finv_[i - 1] * inv_[i];
    }
  }
  constexpr T nCr(int n, int k) const noexcept {
    if (n < k || n < 0 || k < 0)
      return 0;
    return fact_[n] * finv_[k] * finv_[n - k];
  }
  constexpr T nPr(int n, int k) const noexcept {
    if (n < k || n < 0 || k < 0)
      return 0;
    return fact_[n] * finv_[n - k];
  }
  constexpr T nHr(int n, int k) const noexcept { return nCr(n + k - 1, k); }
  constexpr T fact(int n) const noexcept {
    if (n < 0)
      return 0;
    return fact_[n];
  }
  constexpr T inv(int n) const noexcept {
    if (n < 0)
      return 0;
    return inv_[n];
  }
  constexpr T finv(int n) const noexcept {
    if (n < 0)
      return 0;
    return finv_[n];
  }
};

signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(15);
  //---------------------------------------------

  int a, b, c, d;

  BC<mint> bc(2000000 + 10);
  cin >> a >> b >> c >> d;
  mint ans = 0;
  for (int i = a + 1; i <= c; i++) {
    ans += bc.fact(i + d) * bc.finv(i) * bc.finv(d);
  }
  for (int i = b + 1; i <= d; i++) {
    ans += bc.fact(i + c) * bc.finv(i) * bc.finv(c);
  }
  ans += bc.fact(a + b) * bc.finv(a) * bc.finv(b);
  cout << ans.val() << endl;
}