Submission #3601883

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Source Code Expand

#include<bits/stdc++.h>
using namespace std;
#define ll long long
int main(){
  int n,a;
  cin>>n;
  map<int,int> ma;
  for(int i=0;i<n;i++){
    cin>>a;
    ma[a]++;
    if(n%2==0){
      if(a>=n||a%2==0||ma[a]>2){
        cout<<0;
        return 0;
      }
    }else{
      if(a>=n||a%2==1||ma[a]>2||ma[0]>1){
        cout<<0;
        return 0;
      }
    }
  }
  if(n%2==0){
    for(int i=1;i<n;i+=2){
      if(ma[i]!=2){
        cout<<0;
        return 0;
      }
    }
    ll cnt=1;
    for(int i=0;i<n/2;i++){
      cnt*=2;
      cnt%=1000000007;
    }
    cout<<cnt;
  }else{
    if(ma[0]!=1){
      cout<<0;
      return 0;
    }
    for(int i=2;i<n;i+=2){
      if(ma[i]!=2){
        cout<<0;
        return 0;
      }
    }
    ll cnt=1;
    for(int i=0;i<n/2;i++){
      cnt*=2;
      cnt%=1000000007;
    }
    cout<<cnt;
  }
}

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