Problem p02768 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#include <type_traits>
using namespace std;

using ll = int64_t;

#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define ddrep(i, n) for (int i = n; i > 0; --i)
#define srep(i, s, t) for (int i = s; i < t; ++i)
#define ssrep(i, s, t) for (int i = s; i <= t; ++i)

#define rng(a) a.begin(), a.end()
#define pb push_back
#define eb emplace_back
#define fi first
#define se second

#define chmax(x, y) (x = max(x, y))
#define chmin(x, y) (x = min(x, y))

using pi = pair<int, int>;
using vi = vector<int>;
using vvi = vector<vi>;
using ld = long double;

template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << "(" << p.first << "," << p.second << ")";
  return os;
}

template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "{";
  rep(i, (int)v.size()) {
    if (i)
      os << ",";
    os << v[i];
  }
  os << "}";
  return os;
}

template <typename T, size_t S> void printArray(const T (&array)[S]) {
  for (auto val : array)
    std::cout << val << ", ";
  std::cout << "\n";
}

const int mod = 1e9 + 7;
const int inf = 1e9 + 5;

inline ll mypwn(ll x, ll n) {
  if (n == 0)
    return 1;
  if (n % 2 == 0)
    return mypwn(x * x % mod, n / 2);
  else
    return x * mypwn(x, n - 1) % mod;
}

inline int madd(int x, int y) {
  x += y;
  if (x >= mod)
    x -= mod;
  return x;
}
inline int msub(int x, int y) {
  x -= y;
  if (x < 0)
    x += mod;
  return x;
}
inline int mmul(int x, int y) { return 1ll * x * y % mod; }

const int MAX = 1e5 + 5;
ll finv[MAX], inv[MAX];

void initComb() {
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  srep(i, 2, MAX) {
    inv[i] = mod - inv[mod % i] * (mod / i) % mod;
    finv[i] = finv[i - 1] * inv[i] % mod;
  }
}
ll comb(ll n, ll k) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  ll ret = 1;
  rep(i, k) ret = mmul(ret, n - i);
  return mmul(ret, finv[k]);
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << std::setprecision(10);

  int n, a, b;
  std::cin >> n >> a >> b;
  if (n == 2) {
    std::cout << '0' << "\n";
    return 0;
  }
  ll ans = mypwn(2, n) - 1;
  initComb();
  ans = msub(ans, comb(n, a));
  ans = msub(ans, comb(n, b));
  std::cout << ans << "\n";
}


Fixed submission:
#include <bits/stdc++.h>
#include <type_traits>
using namespace std;

using ll = int64_t;

#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define ddrep(i, n) for (int i = n; i > 0; --i)
#define srep(i, s, t) for (int i = s; i < t; ++i)
#define ssrep(i, s, t) for (int i = s; i <= t; ++i)

#define rng(a) a.begin(), a.end()
#define pb push_back
#define eb emplace_back
#define fi first
#define se second

#define chmax(x, y) (x = max(x, y))
#define chmin(x, y) (x = min(x, y))

using pi = pair<int, int>;
using vi = vector<int>;
using vvi = vector<vi>;
using ld = long double;

template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << "(" << p.first << "," << p.second << ")";
  return os;
}

template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "{";
  rep(i, (int)v.size()) {
    if (i)
      os << ",";
    os << v[i];
  }
  os << "}";
  return os;
}

template <typename T, size_t S> void printArray(const T (&array)[S]) {
  for (auto val : array)
    std::cout << val << ", ";
  std::cout << "\n";
}

const int mod = 1e9 + 7;
const int inf = 1e9 + 5;

inline ll mypwn(ll x, ll n) {
  if (n == 0)
    return 1;
  if (n % 2 == 0)
    return mypwn(x * x % mod, n / 2);
  else
    return x * mypwn(x, n - 1) % mod;
}

inline int madd(int x, int y) {
  x += y;
  if (x >= mod)
    x -= mod;
  return x;
}
inline int msub(int x, int y) {
  x -= y;
  if (x < 0)
    x += mod;
  return x;
}
inline int mmul(int x, int y) { return 1ll * x * y % mod; }

const int MAX = 2 * 1e5 + 5;
ll finv[MAX], inv[MAX];

void initComb() {
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  srep(i, 2, MAX) {
    inv[i] = mod - inv[mod % i] * (mod / i) % mod;
    finv[i] = finv[i - 1] * inv[i] % mod;
  }
}
ll comb(ll n, ll k) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  ll ret = 1;
  rep(i, k) ret = mmul(ret, n - i);
  return mmul(ret, finv[k]);
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << std::setprecision(10);

  int n, a, b;
  std::cin >> n >> a >> b;
  if (n == 2) {
    std::cout << '0' << "\n";
    return 0;
  }
  ll ans = mypwn(2, n) - 1;
  initComb();
  ans = msub(ans, comb(n, a));
  ans = msub(ans, comb(n, b));
  std::cout << ans << "\n";
}