Language: C++

#pragma GCC target("avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h>
using namespace std;
using ll = long long;

using i64 = int_fast64_t;
using P = pair<i64,i64>;
constexpr i64 MAX = 510000;
constexpr i64 MOD = 1000000007;
i64 fac[MAX], finv[MAX], inv[MAX];
template <i64 modulus>
class modcal
{

public:
  i64 a;

  constexpr modcal(const i64 x = 0) noexcept : a(x % modulus) {}
  constexpr i64 &value() noexcept { return a; }
  constexpr const i64 &value() const noexcept { return a; }
  constexpr modcal operator+(const modcal rhs) const noexcept
  {
    return modcal(*this) += rhs;
  }
  constexpr modcal operator-(const modcal rhs) const noexcept
  {
    return modcal(*this) -= rhs;
  }
  constexpr modcal operator*(const modcal rhs) const noexcept
  {
    return modcal(*this) *= rhs;
  }
  constexpr modcal operator/(const modcal rhs) noexcept
  {
    return modcal(*this) /= rhs;
  }
  constexpr modcal &operator+=(const modcal rhs) noexcept
  {
    a += rhs.a;
    if (a >= modulus)
    {
      a -= modulus;
    }
    return *this;
  }
  constexpr modcal &operator-=(const modcal rhs) noexcept
  {
    if (a < rhs.a)
    {
      a += modulus;
    }
    a -= rhs.a;
    return *this;
  }
  constexpr modcal &operator*=(const modcal rhs) noexcept
  {
    a = a * rhs.a % modulus;
    return *this;
  }
  constexpr modcal &operator/=(modcal rhs) noexcept
  {
    i64 exp = modulus - 2;
    while (exp)
    {
      if (exp % 2)
      {
        *this *= rhs;
      }
      rhs *= rhs;
      exp /= 2;
    }
    return *this;
  }

  void COMninit()
  {
    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 % modulus;
      inv[i] = MOD - inv[modulus % i] * (modulus / i) % modulus;
      finv[i] = finv[i - 1] * inv[i] % modulus;
    }
  }
  i64 COMn(i64 n, i64 k)
  {
    if (n < k)
      return 0;
    if (n < 0 || k < 0)
      return 0;
    return fac[n] * (finv[k] * finv[n - k] % modulus) % modulus;
  }
  constexpr modcal<1000000007> modpow(const modcal<1000000007> &a, i64 n)
  {
    if (n == 0)
      return 1;
    auto t = modpow(a, n / 2);
    t = t * t;
    if (n & 1)
      t = t * a;
    return t;
  }
};
using modc = modcal<1000000007>;
int main(){
ios::sync_with_stdio(false);
std::cin.tie(nullptr);
    modc n;
    cin >> n.a;
    vector<i64> p(n.a);
    modc ans = 0;
    ans.a = 0;
    set<i64> minus;
    for(int i = 0; i < n.a; i++){
        cin >> p[i];

        if(p[i] == -1){
            minus.insert(i);
        } else
            p[i]--;

    }
    set<P> original;
    for(i64 i = 0; i < n.a; i++){
        if(p[i] != -1){
            original.insert(make_pair(min(p[i],i),max(p[i], i)));
        }
    }
    ans.a += original.size();
    set<P> st;
    n -= 1;
    ans *= ans.modpow(n,minus.size());
    n += 1;
    for(auto v : minus){
        for(int i = 0; i < n.a; i++){
            if(v != i)
                st.insert(make_pair(min(v,p[i]),max(v,p[i]));
        }
    }
    ans += st.size();
    cout << ans.a << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:141:61: error: expected ')' before ';' token
  141 |                 st.insert(make_pair(min(v,p[i]),max(v,p[i]));
      |                          ~                                  ^
      |                                                             )