Problem p02782 (C++)

Buggy submission (status: Runtime Error):
/*
confirm 0LL and 1LL
confirm cornercases such as 0
confirm times of cin < 10^6
*/
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using P = pair<ll, ll>;
using Pld = pair<ld, ld>;
using Vec = vector<ll>;
using VecP = vector<P>;
using VecB = vector<bool>;
using VecC = vector<char>;
using VecD = vector<ld>;
using VecS = vector<string>;
using VecVec = vector<Vec>;
using Graph = vector<VecP>;
template <typename T> using Vec1 = vector<T>;
template <typename T> using Vec2 = vector<Vec1<T>>;
#define REP(i, m, n) for (ll(i) = (m); (i) < (n); ++(i))
#define REPN(i, m, n) for (ll(i) = (m); (i) <= (n); ++(i))
#define REPR(i, m, n) for (ll(i) = (m)-1; (i) >= (n); --(i))
#define REPNR(i, m, n) for (ll(i) = (m); (i) >= (n); --(i))
#define rep(i, n) REP(i, 0, n)
#define repn(i, n) REPN(i, 1, n)
#define repr(i, n) REPR(i, n, 0)
#define repnr(i, n) REPNR(i, n, 1)
#define all(s) (s).begin(), (s).end()
#define pb push_back
#define mp make_pair
#define fs first
#define sc second
template <typename T> bool chmax(T &a, const T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> bool chmin(T &a, const T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> ll pow2(const T n) { return (1LL << n); }
template <typename T> void cosp(const T n) { cout << n << ' '; }
template <typename T> void co(const T n) { cout << n << endl; }
template <typename T1, typename T2> void co(pair<T1, T2> p) {
  cout << p.fs << ' ' << p.sc << endl;
}
template <typename T> void co(const Vec1<T> &v) {
  for (T i : v)
    cosp(i);
  cout << endl;
}
template <typename T> void co(initializer_list<T> v) {
  for (T i : v)
    cosp(i);
  cout << endl;
}
template <typename T> void ce(const T n) { cerr << n << endl; }
void sonic() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
}
void setp(const ll n) { cout << fixed << setprecision(n); }
const ll INF = 1e9 + 1;
const ll LINF = 1e18 + 1;
const ll MOD = 1e9 + 7;
// const ll MOD = 998244353;
const ld PI = acos(-1);
const ld EPS = 1e-11;

Vec fac, finv;

ll PowMod(ll a, ll n) {
  if (n == 1)
    return a;
  if (n % 2 == 0)
    return PowMod(a * a % MOD, n / 2);
  return a * PowMod(a * a % MOD, n / 2) % MOD;
}

ll combi(ll n, ll k) { return fac[n] * finv[k] % MOD * finv[n - k] % MOD; }

void init(ll n) {
  fac.resize(n + 1);
  fac[0] = 1;
  repn(i, n) fac[i] = (fac[i - 1] * i) % MOD;
  finv.resize(n + 1);
  finv[n] = PowMod(fac[n], MOD - 2);
  repr(i, n) finv[i] = (finv[i + 1] * (i + 1)) % MOD;
  finv[0] = 1;
}

int main(void) {
  ll r1, c1, r2, c2;
  cin >> r1 >> c1 >> r2 >> c2;
  init(1e6);

  ll ans = 0;
  REPN(i, r1 + 1, r2 + 1) {
    ans += combi(c2 + i, c2);
    ans %= MOD;
  }
  REPN(i, r1 + 1, r2 + 1) {
    ans -= combi(c1 + i - 1, c1 - 1);
    ans %= MOD;
  }
  ans += MOD;
  ans %= MOD;
  co(ans);

  return 0;
}


Fixed submission:
/*
confirm 0LL and 1LL
confirm cornercases such as 0
confirm times of cin < 10^6
*/
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using P = pair<ll, ll>;
using Pld = pair<ld, ld>;
using Vec = vector<ll>;
using VecP = vector<P>;
using VecB = vector<bool>;
using VecC = vector<char>;
using VecD = vector<ld>;
using VecS = vector<string>;
using VecVec = vector<Vec>;
using Graph = vector<VecP>;
template <typename T> using Vec1 = vector<T>;
template <typename T> using Vec2 = vector<Vec1<T>>;
#define REP(i, m, n) for (ll(i) = (m); (i) < (n); ++(i))
#define REPN(i, m, n) for (ll(i) = (m); (i) <= (n); ++(i))
#define REPR(i, m, n) for (ll(i) = (m)-1; (i) >= (n); --(i))
#define REPNR(i, m, n) for (ll(i) = (m); (i) >= (n); --(i))
#define rep(i, n) REP(i, 0, n)
#define repn(i, n) REPN(i, 1, n)
#define repr(i, n) REPR(i, n, 0)
#define repnr(i, n) REPNR(i, n, 1)
#define all(s) (s).begin(), (s).end()
#define pb push_back
#define mp make_pair
#define fs first
#define sc second
template <typename T> bool chmax(T &a, const T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> bool chmin(T &a, const T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> ll pow2(const T n) { return (1LL << n); }
template <typename T> void cosp(const T n) { cout << n << ' '; }
template <typename T> void co(const T n) { cout << n << endl; }
template <typename T1, typename T2> void co(pair<T1, T2> p) {
  cout << p.fs << ' ' << p.sc << endl;
}
template <typename T> void co(const Vec1<T> &v) {
  for (T i : v)
    cosp(i);
  cout << endl;
}
template <typename T> void co(initializer_list<T> v) {
  for (T i : v)
    cosp(i);
  cout << endl;
}
template <typename T> void ce(const T n) { cerr << n << endl; }
void sonic() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
}
void setp(const ll n) { cout << fixed << setprecision(n); }
const ll INF = 1e9 + 1;
const ll LINF = 1e18 + 1;
const ll MOD = 1e9 + 7;
// const ll MOD = 998244353;
const ld PI = acos(-1);
const ld EPS = 1e-11;

Vec fac, finv;

ll PowMod(ll a, ll n) {
  if (n == 1)
    return a;
  if (n % 2 == 0)
    return PowMod(a * a % MOD, n / 2);
  return a * PowMod(a * a % MOD, n / 2) % MOD;
}

ll combi(ll n, ll k) { return fac[n] * finv[k] % MOD * finv[n - k] % MOD; }

void init(ll n) {
  fac.resize(n + 1);
  fac[0] = 1;
  repn(i, n) fac[i] = (fac[i - 1] * i) % MOD;
  finv.resize(n + 1);
  finv[n] = PowMod(fac[n], MOD - 2);
  repr(i, n) finv[i] = (finv[i + 1] * (i + 1)) % MOD;
  finv[0] = 1;
}

int main(void) {
  ll r1, c1, r2, c2;
  cin >> r1 >> c1 >> r2 >> c2;
  init(3e6);

  ll ans = 0;
  REPN(i, r1 + 1, r2 + 1) {
    ans += combi(c2 + i, c2);
    ans %= MOD;
  }
  REPN(i, r1 + 1, r2 + 1) {
    ans -= combi(c1 + i - 1, c1 - 1);
    ans %= MOD;
  }
  ans += MOD;
  ans %= MOD;
  co(ans);

  return 0;
}