Problem p02782 (C++)

Buggy submission (status: Runtime Error):
#pragma GCC optimize("O3")
#pragma GCC target("sse4")

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

typedef long long ll;
typedef long double ld;
typedef complex<ld> cd;

typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<ld, ld> pd;

typedef vector<int> vi;
typedef vector<ld> vd;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
typedef vector<cd> vcd;

template <class T>
using Tree =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

#define FOR(i, a, b) for (int i = a; i < (b); i++)
#define F0R(i, a) for (int i = 0; i < (a); i++)
#define FORd(i, a, b) for (int i = (b)-1; i >= a; i--)
#define F0Rd(i, a) for (int i = (a)-1; i >= 0; i--)

#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound
#define all(x) x.begin(), x.end()

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

const int MOD = 1000000007;
const ll INF = 1e18;
const int MX = 1000001; // check the limits, dummy

ll modExp(ll base, ll power) {
  if (power == 0) {
    return 1;
  } else {
    ll cur = modExp(base, power / 2);
    cur = cur * cur;
    cur = cur % MOD;
    if (power % 2 == 1)
      cur = cur * base;
    cur = cur % MOD;
    return cur;
  }
}

ll inv(ll base) {
  int g = MOD, r = base, x = 0, y = 1;
  while (r != 0) {
    int q = g / r;
    g %= r;
    swap(g, r);
    x -= q * y;
    swap(x, y);
  }
  return x < 0 ? x + MOD : x;
}

ll mul(ll A, ll B) { return (A * B) % MOD; }

ll add(ll A, ll B) { return (A + B) % MOD; }

ll dvd(ll A, ll B) { return mul(A, inv(B)); }

ll sub(ll A, ll B) { return (A - B + MOD) % MOD; }

ll *facs = new ll[MX];
ll *facInvs = new ll[MX];

ll choose(ll a, ll b) {
  if (b > a)
    return 0;
  if (a < 0)
    return 0;
  if (b < 0)
    return 0;
  ll cur = facs[a];
  cur = mul(cur, facInvs[b]);
  cur = mul(cur, facInvs[a - b]);
  return cur;
}

void initFacs() {
  facs[0] = 1;
  facInvs[0] = 1;
  FOR(i, 1, MX) {
    facs[i] = (facs[i - 1] * i) % MOD;
    facInvs[i] = inv(facs[i]);
  }
}

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  initFacs();
  ll R1, R2, C1, C2;
  cin >> R1 >> C1 >> R2 >> C2;
  ll ans = 0;
  R1--;
  FOR(i, C1, C2 + 1) {
    ans += choose(i + R2 + 1, R2);
    ans += MOD - choose(i + R1 + 1, R1);
    ans %= MOD;
  }
  cout << ans << endl;
  return 0;
}

// read the question correctly (ll vs int)
// template by bqi343


Fixed submission:
#pragma GCC optimize("O3")
#pragma GCC target("sse4")

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

typedef long long ll;
typedef long double ld;
typedef complex<ld> cd;

typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<ld, ld> pd;

typedef vector<int> vi;
typedef vector<ld> vd;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
typedef vector<cd> vcd;

template <class T>
using Tree =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

#define FOR(i, a, b) for (int i = a; i < (b); i++)
#define F0R(i, a) for (int i = 0; i < (a); i++)
#define FORd(i, a, b) for (int i = (b)-1; i >= a; i--)
#define F0Rd(i, a) for (int i = (a)-1; i >= 0; i--)

#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound
#define all(x) x.begin(), x.end()

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

const int MOD = 1000000007;
const ll INF = 1e18;
const int MX = 3000001; // check the limits, dummy

ll modExp(ll base, ll power) {
  if (power == 0) {
    return 1;
  } else {
    ll cur = modExp(base, power / 2);
    cur = cur * cur;
    cur = cur % MOD;
    if (power % 2 == 1)
      cur = cur * base;
    cur = cur % MOD;
    return cur;
  }
}

ll inv(ll base) {
  int g = MOD, r = base, x = 0, y = 1;
  while (r != 0) {
    int q = g / r;
    g %= r;
    swap(g, r);
    x -= q * y;
    swap(x, y);
  }
  return x < 0 ? x + MOD : x;
}

ll mul(ll A, ll B) { return (A * B) % MOD; }

ll add(ll A, ll B) { return (A + B) % MOD; }

ll dvd(ll A, ll B) { return mul(A, inv(B)); }

ll sub(ll A, ll B) { return (A - B + MOD) % MOD; }

ll *facs = new ll[MX];
ll *facInvs = new ll[MX];

ll choose(ll a, ll b) {
  if (b > a)
    return 0;
  if (a < 0)
    return 0;
  if (b < 0)
    return 0;
  ll cur = facs[a];
  cur = mul(cur, facInvs[b]);
  cur = mul(cur, facInvs[a - b]);
  return cur;
}

void initFacs() {
  facs[0] = 1;
  facInvs[0] = 1;
  FOR(i, 1, MX) {
    facs[i] = (facs[i - 1] * i) % MOD;
    facInvs[i] = inv(facs[i]);
  }
}

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  initFacs();
  ll R1, R2, C1, C2;
  cin >> R1 >> C1 >> R2 >> C2;
  ll ans = 0;
  R1--;
  FOR(i, C1, C2 + 1) {
    ans += choose(i + R2 + 1, R2);
    ans += MOD - choose(i + R1 + 1, R1);
    ans %= MOD;
  }
  cout << ans << endl;
  return 0;
}

// read the question correctly (ll vs int)
// template by bqi343