PAT-1041 Be Unique

Being unique is so important to people on Mars that even their lottery is designed in a unique way. The rule of winning is simple: one bets on a number chosen from [1, 10⁴]. The first one who bets on a unique number wins. For example, if there are 7 people betting on 5 31 5 88 67 88 17, then the second one who bets on 31 wins.

Input Specification:

Each input file contains one test case. Each case contains a line which begins with a positive integer N (<=10⁵) and then followed by N bets. The numbers are separated by a space.

Output Specification:

For each test case, print the winning number in a line. If there is no winner, print "None" instead.

Sample Input 1:

7 5 31 5 88 67 88 17

Sample Output 1:

31

Sample Input 2:

5 888 666 666 888 888

Sample Output 2:

None

 #include <iostream>
 #include <set>
 using namespace std;

 int main(){
     int n;
     int i,t;
     cin>>n;
     set<int> s,s1;
     int record[n];
     cin>>t;
     s.insert(t);
     s1.insert(t);
     record[] = t;
     for(i = ; i < n; i++){
         cin>>t;
         record[i] = t;
         if(s1.find(t) != s1.end() && s.find(t) != s.end()){
             s.erase(t);
         }
         else if(s1.find(t) == s1.end()){
             s.insert(t);
             s1.insert(t);
         }

     }
     if(s.empty()){
         cout<<"None";
     }else{
         i = ;
         while(s.find(record[i]) == s.end()){
             i++;
         }
         cout<<record[i]<<endl;
     }
     return ;
 }