Problem p02782 (C++)

Buggy submission (status: Runtime Error):
// #pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define N 1000000007
#define N2 998244353
#define Nmax 1000005
#define INF (ll)1e18
#define pll pair<ll, ll>
#define mp make_pair
#define fi first
#define se second
#define vv vector
#define rep(i, n) rep2(i, 0, n)
#define rep2(i, m, n) for (ll i = m; i < (n); i++)
#define repr(i, n) repr2(i, n, 0)
#define repr2(i, m, n) for (ll i = m; i >= (n); i--)
#define get(n)                                                                 \
  ll(n);                                                                       \
  scanf("%lld", &(n));
#define get2(n, k)                                                             \
  ll(n), (k);                                                                  \
  scanf("%lld%lld", &(n), &(k));
#define get3(n, m, k)                                                          \
  ll(n), (m), (k);                                                             \
  scanf("%lld%lld%lld", &(n), &(m), &(k));
#define gets(s)                                                                \
  string(s);                                                                   \
  cin >> (s);
#define ALL(c) (c).begin(), (c).end()
#define fill_nums(A, n)                                                        \
  vector<ll> A((n));                                                           \
  for (ll i = 0; i < n; i++)                                                   \
    scanf("%lld", &A[i]);
#define fill_edges(adj, m)                                                     \
  for (ll i = 0; i < m; i++) {                                                 \
    ll a, b;                                                                   \
    scanf("%lld %lld", &a, &b);                                                \
    adj[a - 1].pb(b - 1);                                                      \
    adj[b - 1].pb(a - 1);                                                      \
  }
#define fill_direct(adj, m)                                                    \
  for (ll i = 0; i < m; i++) {                                                 \
    ll a, b;                                                                   \
    scanf("%lld %lld", &a, &b);                                                \
    adj[a - 1].pb(b - 1);                                                      \
  }
#define StarBurstStream                                                        \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(0); // cout.tie(0);
#define pi 3.1415926535897
#define db long double /* print with %Lf */
#define EPS 1e-9
#define flu fflush(stdout)
#define imp                                                                    \
  {                                                                            \
    cout << "0\n";                                                             \
    return 0;                                                                  \
  }
#define yup                                                                    \
  {                                                                            \
    cout << "YES\n";                                                           \
    return 0;                                                                  \
  }
#define debug_vec(vec, n)                                                      \
  {                                                                            \
    rep(idxi, n) cout << vec[idxi] << " ";                                     \
    cout << "\n";                                                              \
  }
#define debug_pvec(vec, n)                                                     \
  {                                                                            \
    rep(idxi, n) cout << vec[idxi].fi << "-" << vec[idxi].se << "  ";          \
    cout << "\n";                                                              \
  }
#define debug_set(seta)                                                        \
  {                                                                            \
    cout << seta.size() << "\n";                                               \
    for (auto idxi : seta)                                                     \
      cout << idxi << " ";                                                     \
    cout << "\n";                                                              \
  }
#define debug_map(mappa)                                                       \
  {                                                                            \
    cout << mappa.size() << "\n";                                              \
    for (auto idxi : mappa)                                                    \
      cout << idxi.fi << "-" << idxi.se << "  ";                               \
    cout << "\n";                                                              \
  }
#define debug_vecvec(vec, n)                                                   \
  {                                                                            \
    rep(idxi, n) {                                                             \
      for (auto idxi2 : vec[idxi])                                             \
        cout << idxi2 << " ";                                                  \
      cout << "\n";                                                            \
    }                                                                          \
  }

// LOOK AT THESE BEFORE SUBMISSION
// LOOK AT THESE BEFORE SUBMISSION
// ============================================================
// Nmax value and is index access offset taking it beyond Nmax.
// Precision error in case of real numbers.
// N vs N2 chosen correctly.
// Modulo applied everywhere.
// Flush in case of interactive.
// Don't erase value in multiset.
// Check for array indices out of bound (in pre or suff sums).
// Correct return value for functions.
// Confirm the letter case of yes and no.
// Dont paste code two times in the text file.
// ============================================================

vector<ll> facts, invfacts;

ll power(ll x, ll n, ll d) {
  ll val = (x % d), res = 1;
  while (n > 0) {
    if (n & 1)
      res = (res * val) % d;
    val = (val * val) % d;
    n = n >> 1;
  }
  return (res + d) % d;
}

ll nck(ll n, ll k, ll d) {
  if (k > n)
    return 0;
  return (facts[n] * invfacts[k] % d * invfacts[n - k] % d + d) % d;
}

ll npk(ll n, ll k, ll d) {
  if (k > n)
    return 0;
  return (facts[n] * invfacts[n - k] % d + d) % d;
}

void initialize_facts(ll n, ll mod) {
  facts.resize(n + 1);
  invfacts.resize(n + 1);
  facts[0] = 1;
  invfacts[0] = 1;

  for (ll i = 1; i <= n; i++) {
    facts[i] = (facts[i - 1] * i) % mod;
    invfacts[i] = power(facts[i], mod - 2, mod);
  }
}

int main() {

  initialize_facts(Nmax, N);
  get2(r1, c1);
  get2(r2, c2);
  ll diff = r2 - r1, diff2 = c2 - c1;

  ll ans = 0;

  rep(i, diff + 1) {
    ll up = r1 + i + c1;
    ans = (ans + nck(up + diff2 + 1, c1 + diff2, N)) % N;
    ans = (ans - nck(up, c1 - 1, N)) % N;
  }

  printf("%lld\n", (ans + N) % N);
  return 0;
}

Fixed submission:
// #pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define N 1000000007
#define N2 998244353
#define Nmax 3000005
#define INF (ll)1e18
#define pll pair<ll, ll>
#define mp make_pair
#define fi first
#define se second
#define vv vector
#define rep(i, n) rep2(i, 0, n)
#define rep2(i, m, n) for (ll i = m; i < (n); i++)
#define repr(i, n) repr2(i, n, 0)
#define repr2(i, m, n) for (ll i = m; i >= (n); i--)
#define get(n)                                                                 \
  ll(n);                                                                       \
  scanf("%lld", &(n));
#define get2(n, k)                                                             \
  ll(n), (k);                                                                  \
  scanf("%lld%lld", &(n), &(k));
#define get3(n, m, k)                                                          \
  ll(n), (m), (k);                                                             \
  scanf("%lld%lld%lld", &(n), &(m), &(k));
#define gets(s)                                                                \
  string(s);                                                                   \
  cin >> (s);
#define ALL(c) (c).begin(), (c).end()
#define fill_nums(A, n)                                                        \
  vector<ll> A((n));                                                           \
  for (ll i = 0; i < n; i++)                                                   \
    scanf("%lld", &A[i]);
#define fill_edges(adj, m)                                                     \
  for (ll i = 0; i < m; i++) {                                                 \
    ll a, b;                                                                   \
    scanf("%lld %lld", &a, &b);                                                \
    adj[a - 1].pb(b - 1);                                                      \
    adj[b - 1].pb(a - 1);                                                      \
  }
#define fill_direct(adj, m)                                                    \
  for (ll i = 0; i < m; i++) {                                                 \
    ll a, b;                                                                   \
    scanf("%lld %lld", &a, &b);                                                \
    adj[a - 1].pb(b - 1);                                                      \
  }
#define StarBurstStream                                                        \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(0); // cout.tie(0);
#define pi 3.1415926535897
#define db long double /* print with %Lf */
#define EPS 1e-9
#define flu fflush(stdout)
#define imp                                                                    \
  {                                                                            \
    cout << "0\n";                                                             \
    return 0;                                                                  \
  }
#define yup                                                                    \
  {                                                                            \
    cout << "YES\n";                                                           \
    return 0;                                                                  \
  }
#define debug_vec(vec, n)                                                      \
  {                                                                            \
    rep(idxi, n) cout << vec[idxi] << " ";                                     \
    cout << "\n";                                                              \
  }
#define debug_pvec(vec, n)                                                     \
  {                                                                            \
    rep(idxi, n) cout << vec[idxi].fi << "-" << vec[idxi].se << "  ";          \
    cout << "\n";                                                              \
  }
#define debug_set(seta)                                                        \
  {                                                                            \
    cout << seta.size() << "\n";                                               \
    for (auto idxi : seta)                                                     \
      cout << idxi << " ";                                                     \
    cout << "\n";                                                              \
  }
#define debug_map(mappa)                                                       \
  {                                                                            \
    cout << mappa.size() << "\n";                                              \
    for (auto idxi : mappa)                                                    \
      cout << idxi.fi << "-" << idxi.se << "  ";                               \
    cout << "\n";                                                              \
  }
#define debug_vecvec(vec, n)                                                   \
  {                                                                            \
    rep(idxi, n) {                                                             \
      for (auto idxi2 : vec[idxi])                                             \
        cout << idxi2 << " ";                                                  \
      cout << "\n";                                                            \
    }                                                                          \
  }

// LOOK AT THESE BEFORE SUBMISSION
// LOOK AT THESE BEFORE SUBMISSION
// ============================================================
// Nmax value and is index access offset taking it beyond Nmax.
// Precision error in case of real numbers.
// N vs N2 chosen correctly.
// Modulo applied everywhere.
// Flush in case of interactive.
// Don't erase value in multiset.
// Check for array indices out of bound (in pre or suff sums).
// Correct return value for functions.
// Confirm the letter case of yes and no.
// Dont paste code two times in the text file.
// ============================================================

vector<ll> facts, invfacts;

ll power(ll x, ll n, ll d) {
  ll val = (x % d), res = 1;
  while (n > 0) {
    if (n & 1)
      res = (res * val) % d;
    val = (val * val) % d;
    n = n >> 1;
  }
  return (res + d) % d;
}

ll nck(ll n, ll k, ll d) {
  if (k > n)
    return 0;
  return (facts[n] * invfacts[k] % d * invfacts[n - k] % d + d) % d;
}

ll npk(ll n, ll k, ll d) {
  if (k > n)
    return 0;
  return (facts[n] * invfacts[n - k] % d + d) % d;
}

void initialize_facts(ll n, ll mod) {
  facts.resize(n + 1);
  invfacts.resize(n + 1);
  facts[0] = 1;
  invfacts[0] = 1;

  for (ll i = 1; i <= n; i++) {
    facts[i] = (facts[i - 1] * i) % mod;
    invfacts[i] = power(facts[i], mod - 2, mod);
  }
}

int main() {

  initialize_facts(Nmax, N);
  get2(r1, c1);
  get2(r2, c2);
  ll diff = r2 - r1, diff2 = c2 - c1;

  ll ans = 0;

  rep(i, diff + 1) {
    ll up = r1 + i + c1;
    ans = (ans + nck(up + diff2 + 1, c1 + diff2, N)) % N;
    ans = (ans - nck(up, c1 - 1, N)) % N;
  }

  printf("%lld\n", (ans + N) % N);
  return 0;
}