Language: C++

#include <bits/stdc++.h>
#define REP(i,n) for(int i = 0; i < n; i++)
#define REPR(i,n) for(int i = n; i >= 0; i--)
#define FOR(i,m, n) for(int i = m-1; i < n; i++)
#define ALL(v) v.begin(), v.end()
#define chmax(x,y) (x = max(x,y))
#define chmin(x,y) (x = min(x,y))
#define FILL2D(A,c) fill(A[0], A[0] +sizeof(A)/sizeof(**A),c)
#define FILL3D(A,c) fill(A[0][0], A[0][0] +sizeof(A)/sizeof(***A),c)
//vector<vector<要素の型>> 変数名(要素数1, vector<要素の型>(要素数2, 初期値))
//vector<intなど> 変数名(要素数,初期値)
using namespace std;
typedef long long ll;
const int MAX = 510000;
const int INF =2000000000;
const int MOD = 1000000007;
//gcd,lcmセット
ll gcd(ll a, ll b){
   if (a%b == 0) return b;
   else return gcd(b, a%b);
}
ll lcm(ll a, ll b){	
   return a*b/gcd(a, b);
}
int pow_kai(int a, int n){//aのn乗を計算します。
  int x = 1;
  while(n > 0){//全てのbitが捨てられるまで。
    if(n&1){//1番右のbitが1のとき。
      x = x*a;
    }
    a = a*a;
    n >>= 1;//bit全体を右に1つシフトして一番右を捨てる。
  }
  return x;
}
// a^n mod を計算する
long long modPow(long long a, long long n, long long mod) {
    long long res = 1;
    while (n > 0) {
        if (n & 1) res = res * a % mod;
        a = a * a % mod;
        n >>= 1;
    }
    return res;
}

long long fac[MAX], finv[MAX], inv[MAX];

// combinationのテーブルを作る前処理
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}
 
// 二項係数計算
ll COM(int n, int k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}
 
bool isPrime(ll x){
    int i;
    if(x < 2)return false;
    else if(x == 2) return true;
    if(x%2 == 0) return false;
    for(i = 3; i*i <= x; i += 2) if(x%i == 0) return false;
    return true;
}
//dfsではvector<vector<int>> g(n);で◎
int main() {
    ll n, a, b;
    cin >> n >> a >> b;
    COMinit();
    ll v1 = 1;
    for (ll i = n; i > n - a; i--) {
        v1 *= i;
        v1 %= MOD;
    }
    ll v2 = 1;
    for (ll i = n; i > n - b; i--) {
        v2 *= i;
        v2 %= MOD;
    }
    v1 *= finv[a];
    v2 *= finv[b];
    v1 %= MOD;
    v2 %= MOD;
    ll ans = modpow(2, n, MOD) - 1 - v1 - v2;
    ans += 10 * MOD;
    ans %= MOD;
    cout << ans << "\n";
    return 0;
}

Compiler output:
a.cc:60:6: error: redefinition of 'void COMinit()'
   60 | void COMinit() {
      |      ^~~~~~~
a.cc:50:6: note: 'void COMinit()' previously defined here
   50 | void COMinit() {
      |      ^~~~~~~
a.cc: In function 'int main()':
a.cc:105:14: error: 'modpow' was not declared in this scope; did you mean 'modPow'?
  105 |     ll ans = modpow(2, n, MOD) - 1 - v1 - v2;
      |              ^~~~~~
      |              modPow
a.cc:106:15: warning: integer overflow in expression of type 'int' results in '1410065478' [-Woverflow]
  106 |     ans += 10 * MOD;
      |            ~~~^~~~~