Language: C++

#include<iostream>
using namespace std;
int main()
{  
}#include<bits/stdc++.h>
using namespace std;
typedef pair<int, int> pi;
typedef vector<int> vi;
typedef vector<string> vs;
typedef vector<pi> vpi;
typedef vector<vi> vii;
typedef map<int, int> mp;
typedef multiset<int> mset;
typedef long int int32;
typedef unsigned long int uint32;
typedef long long int int64;
typedef unsigned long long int  uint64;
typedef vector<int64> vi64;
#define fast ios_base::sync_with_stdio(0);cin.tie(NULL);cout.tie(NULL)
#define form(i,j,k,l) for(int i=j;i<int(k);i+=l)
#define rform(i,j,k,l) for(int i=int(j);i>int(l);i-=l)
#define rep(i, j) for(int i=0;i<int(j);i++)
#define rrep(i, j) for(int i=int(j);i>=0;i--)
#define all(cont) cont.begin(), cont.end()
#define rall(cont) cont.end(), cont.begin()
#define forc(it, l) for (auto it = l.begin(); it != l.end(); it++)
#define IN(A, B, C) assert( B <= A && A <= C)
#define mp(x,y) make_pair(x,y)
#define pb(x) push_back(x)
#define INF (int)1e9
#define INF64 (int64)1e18
#define EPS 1e-9
#define PI 3.1415926535897932384626433832795
#define MOD 1000000007
#define read(type) readInt<type>()
#define F first
#define S  second
const double pie = acos(-1.0);
template <typename T>
T Max(T x, T y)
{
  return (x > y) ? x : y;
}
template <typename T>
T Min(T x, T y)
{
  return (x > y) ? y : x;
}
int gcd(int n1, int n2)
{
  if (n2 != 0) return gcd(n2, n1 % n2);
  else return n1;
}
#define TRACE

#ifdef TRACE
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) {
  cerr << name << " : " << arg1 << std::endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
  const char* comma = strchr(names + 1, ','); cerr.write(names, comma - names) << " : " << arg1 << " | "; __f(comma + 1, args...);
}
#else
#define trace(...)
#endif
clock_t time_p = clock();
void rtime() { time_p = clock() - time_p; cerr << "Time Taken : " << (float)1000 * (time_p) / CLOCKS_PER_SEC << "\n";}
int binpow(int  a, int  b) {
  if (b == 0)
    return 1;
  int res = binpow(a, b / 2);
  if (b % 2)
    return res * res * a;
  else
    return res * res;
}

int main()
{ fast;
  int n;
  cin >> n;
  int arr[n];
  int count[n] = {0};
  for (int i = 0; i < n; i++)
  { cin >> arr[i];
    count[arr[i]]++;
  }
  int ret;
  if (n % 2 == 0)
    ret = 1;
  else
    ret = 0;
  for (int i = 0; i < n; i++)
  { if (ret == 0 && i % 2 != 0)
      continue;
    if (ret == 1 && i % 2 == 0)
      continue;
    if (i != 0 && count[i] != 2)
    { cout << "0";
      return 0;
    }
    if (i == 0)
    { if (count[i] > 1)
      { cout << "0";
        return 0;
      }
      if (count[i] == 1 && n % 2 == 0)
      { cout << "0";
        return 0;
      }
    }
  }
  cout << binpow(2, n / 2);
  return 0;

}



Compiler output:
a.cc:5:2: error: stray '#' in program
    5 | }#include<bits/stdc++.h>
      |  ^
a.cc:5:3: error: 'include' does not name a type
    5 | }#include<bits/stdc++.h>
      |   ^~~~~~~
a.cc:8:9: error: 'vector' does not name a type
    8 | typedef vector<int> vi;
      |         ^~~~~~
a.cc:9:9: error: 'vector' does not name a type
    9 | typedef vector<string> vs;
      |         ^~~~~~
a.cc:10:9: error: 'vector' does not name a type
   10 | typedef vector<pi> vpi;
      |         ^~~~~~
a.cc:11:9: error: 'vector' does not name a type
   11 | typedef vector<vi> vii;
      |         ^~~~~~
a.cc:12:9: error: 'map' does not name a type; did you mean 'mp'?
   12 | typedef map<int, int> mp;
      |         ^~~
      |         mp
a.cc:13:9: error: 'multiset' does not name a type
   13 | typedef multiset<int> mset;
      |         ^~~~~~~~
a.cc:18:9: error: 'vector' does not name a type
   18 | typedef vector<int64> vi64;
      |         ^~~~~~
a.cc:38:20: error: 'acos' was not declared in this scope
   38 | const double pie = acos(-1.0);
      |                    ^~~~
a.cc: In function 'void __f(const char*, Arg1&&, Args&& ...)':
a.cc:64:23: error: there are no arguments to 'strchr' that depend on a template parameter, so a declaration of 'strchr' must be available [-fpermissive]
   64 |   const char* comma = strchr(names + 1, ','); cerr.write(names, comma - names) << " : " << arg1 << " | "; __f(comma + 1, args...);
      |                       ^~~~~~
a.cc:64:23: note: (if you use '-fpermissive', G++ will accept your code, but allowing the use of an undeclared name is deprecated)
a.cc: At global scope:
a.cc:81:5: error: redefinition of 'int main()'
   81 | int main()
      |     ^~~~
a.cc:3:5: note: 'int main()' previously defined here
    3 | int main()
      |     ^~~~