Submission #7060823

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Source Code Expand

#include<bits/stdc++.h>
using namespace std;
constexpr int64_t mod=1e9+7;

int main()
{
  int n;
  cin>>n;
  std::vector<int> a(n);
  for (int i = 0; i < n; ++i)
  {
    cin>>a[i];    
  }
  sort(a.begin(), a.end());

  if(n%2==0){
    for (int i = 1; i < n; i+=2)
    {
      auto u=upper_bound(a.begin(), a.end(),i);
      auto l=lower_bound(a.begin(), a.end(),i);
      if(u-l!=2) {
        cout<<0;
        return 0;
      }
    }
  }
  else{
    if(upper_bound(a.begin(), a.end(),0)-a.begin()!=1){
      cout<<0;
      return 0;
    }
    for (int i = 2; i < n; i+=2)
    {
      auto u=upper_bound(a.begin(), a.end(),i);
      auto l=lower_bound(a.begin(), a.end(),i);
      if(u-l!=2){
        cout<<0;
        return 0;
      }
    }
  }

  if(n%2!=0) n--;
  int64_t ans=1;
  for (int i = 0; i < n/2; ++i)
  {
    ans*=2;
    ans%=mod;
  }
  cout<<ans;

}

Submission Info

Judge Result