Problem p02782 (C++)

Buggy submission (status: Runtime Error):
// g++ -std=c++11 a.cpp
#include <algorithm>
#include <assert.h>
#include <bitset>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <typeinfo>
#include <unordered_map>
#include <utility>
#include <vector>
#define loop(i, a, b) for (long long i = a; i < b; i++)
#define rep(i, a) loop(i, 0, a)
#define FOR(i, a) for (auto i : a)
#define pb push_back
#define all(in) in.begin(), in.end()
#define shosu(x) fixed << setprecision(x)
#define show1d(v)                                                              \
  {                                                                            \
    rep(_, v.size()) cout << " " << v[_];                                      \
    cout << endl;                                                              \
  }
#define show2d(v)                                                              \
  { rep(__, v.size()) show1d(v[__]); }
using namespace std;
// kaewasuretyuui
typedef long long ll;
#define int ll
typedef int Def;
typedef pair<Def, Def> pii;
typedef vector<Def> vi;
typedef vector<vi> vvi;
typedef vector<pii> vp;
typedef vector<vp> vvp;
typedef vector<string> vs;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef pair<Def, pii> pip;
typedef vector<pip> vip;
// #define mt make_tuple
// typedef tuple<int,int,int,int> tp;
// typedef vector<tp> vt;
template <typename A, typename B> bool cmin(A &a, const B &b) {
  return a > b ? (a = b, true) : false;
}
template <typename A, typename B> bool cmax(A &a, const B &b) {
  return a < b ? (a = b, true) : false;
}
const double PI = acos(-1);
const double EPS = 1e-9;
Def inf = sizeof(Def) == sizeof(long long) ? 2e18 : 1e9 + 10;
int dx[] = {-1, 0, 1, 0};
int dy[] = {0, 1, 0, -1};
#define yes cout << "Yes\n"
#define no cout << "No\n"

// nCr mod m
#define MOD 1000000007
#define M 1000000
vector<ll> fact;
bool h = false;
void init() {
  h = true;
  fact = vector<ll>(M);
  fact[0] = fact[1] = 1;
  loop(i, 2, M) fact[i] = fact[i - 1] * i % MOD;
}
// a^b mod MOD
ll powmod(ll a, ll b, ll m = MOD) {
  ll out = 1;
  ll p = a % m;
  while (b) {
    if (b & 1)
      out = out * p % m;
    p = p * p % m;
    b >>= 1;
  }
  return out;
}
// nCr
ll nCr(ll n, ll r, ll m = MOD) {
  if (!h)
    init();
  if (n < 0 || r < 0 || n < r)
    return 1; //??????
  ll out = fact[n] * powmod(fact[r] * fact[n - r] % m, m - 2, m) % m;
  return out;
}
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

  int a, b, c, d;
  cin >> a >> b >> c >> d;
  int out = 0;
  loop(i, a, c + 1)(out +=
                    MOD + nCr(i + d + 1, d) - nCr(i + b - 1 + 1, b - 1)) %= MOD;
  cout << out << endl;
}


Fixed submission:
// g++ -std=c++11 a.cpp
#include <algorithm>
#include <assert.h>
#include <bitset>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <typeinfo>
#include <unordered_map>
#include <utility>
#include <vector>
#define loop(i, a, b) for (long long i = a; i < b; i++)
#define rep(i, a) loop(i, 0, a)
#define FOR(i, a) for (auto i : a)
#define pb push_back
#define all(in) in.begin(), in.end()
#define shosu(x) fixed << setprecision(x)
#define show1d(v)                                                              \
  {                                                                            \
    rep(_, v.size()) cout << " " << v[_];                                      \
    cout << endl;                                                              \
  }
#define show2d(v)                                                              \
  { rep(__, v.size()) show1d(v[__]); }
using namespace std;
// kaewasuretyuui
typedef long long ll;
#define int ll
typedef int Def;
typedef pair<Def, Def> pii;
typedef vector<Def> vi;
typedef vector<vi> vvi;
typedef vector<pii> vp;
typedef vector<vp> vvp;
typedef vector<string> vs;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef pair<Def, pii> pip;
typedef vector<pip> vip;
// #define mt make_tuple
// typedef tuple<int,int,int,int> tp;
// typedef vector<tp> vt;
template <typename A, typename B> bool cmin(A &a, const B &b) {
  return a > b ? (a = b, true) : false;
}
template <typename A, typename B> bool cmax(A &a, const B &b) {
  return a < b ? (a = b, true) : false;
}
const double PI = acos(-1);
const double EPS = 1e-9;
Def inf = sizeof(Def) == sizeof(long long) ? 2e18 : 1e9 + 10;
int dx[] = {-1, 0, 1, 0};
int dy[] = {0, 1, 0, -1};
#define yes cout << "Yes\n"
#define no cout << "No\n"

// nCr mod m
#define MOD 1000000007
#define M 2200000
vector<ll> fact;
bool h = false;
void init() {
  h = true;
  fact = vector<ll>(M);
  fact[0] = fact[1] = 1;
  loop(i, 2, M) fact[i] = fact[i - 1] * i % MOD;
}
// a^b mod MOD
ll powmod(ll a, ll b, ll m = MOD) {
  ll out = 1;
  ll p = a % m;
  while (b) {
    if (b & 1)
      out = out * p % m;
    p = p * p % m;
    b >>= 1;
  }
  return out;
}
// nCr
ll nCr(ll n, ll r, ll m = MOD) {
  if (!h)
    init();
  if (n < 0 || r < 0 || n < r)
    return 1; //??????
  ll out = fact[n] * powmod(fact[r] * fact[n - r] % m, m - 2, m) % m;
  return out;
}
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

  int a, b, c, d;
  cin >> a >> b >> c >> d;
  int out = 0;
  loop(i, a, c + 1)(out +=
                    MOD + nCr(i + d + 1, d) - nCr(i + b - 1 + 1, b - 1)) %= MOD;
  cout << out << endl;
}