Language: C++

#include <iostream>
#include <cmath>

#define MOD = 10^9 + 7

int main()
{
  int n;
  long long ans = (long long)1;
  cin >> n;
  vector<int> nums(n + 1, 0);
  for (int i = 0; i < n; i++) {
    int num;
    cin >> num;
    nums[num]++;
  }
  //validation
  if (n % 2 == 0) {
    for (int i = 1; i <=n; i++9) {
      if (i % 2 == 1 && nums[i] != 2) {
        cout << 0 << endl;
        return 0;
      }
    }
  } else {
    if (nums[0] != 1) {
      cout << 0 << endl;
      return 0;
    }
    
    for (int i = 1; i <=n; i++9) {
      if (i % 2 == 0 && nums[i] != 2) {
        cout << 0 << endl;
        return 0;
      }
    }
  }
  
  
  for (int i = 1; i <= n/2; i++)
  {
    ans ^= 2;
    ans %= MOD;
  }
  cout << ans << endl;
  return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:10:3: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
   10 |   cin >> n;
      |   ^~~
      |   std::cin
In file included from a.cc:1:
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:11:3: error: 'vector' was not declared in this scope
   11 |   vector<int> nums(n + 1, 0);
      |   ^~~~~~
a.cc:11:10: error: expected primary-expression before 'int'
   11 |   vector<int> nums(n + 1, 0);
      |          ^~~
a.cc:15:5: error: 'nums' was not declared in this scope; did you mean 'num'?
   15 |     nums[num]++;
      |     ^~~~
      |     num
a.cc:19:31: error: expected ')' before numeric constant
   19 |     for (int i = 1; i <=n; i++9) {
      |         ~                     ^
      |                               )
a.cc:19:32: error: expected ';' before ')' token
   19 |     for (int i = 1; i <=n; i++9) {
      |                                ^
      |                                ;
a.cc:26:9: error: 'nums' was not declared in this scope
   26 |     if (nums[0] != 1) {
      |         ^~~~
a.cc:27:7: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   27 |       cout << 0 << endl;
      |       ^~~~
      |       std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:27:20: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   27 |       cout << 0 << endl;
      |                    ^~~~
      |                    std::endl
In file included from /usr/include/c++/14/iostream:41:
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:31:31: error: expected ')' before numeric constant
   31 |     for (int i = 1; i <=n; i++9) {
      |         ~                     ^
      |                               )
a.cc:31:32: error: expected ';' before ')' token
   31 |     for (int i = 1; i <=n; i++9) {
      |                                ^
      |                                ;
a.cc:4:13: error: expected primary-expression before '=' token
    4 | #define MOD = 10^9 + 7
      |             ^
a.cc:43:12: note: in expansion of macro 'MOD'
   43 |     ans %= MOD;
      |            ^~~
a.cc:45:3: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   45 |   cout << ans << endl;
      |   ^~~~
      |   std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:45:18: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   45 |   cout << ans << endl;
      |                  ^~~~
      |                  std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~