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[0] = t;
    for(i = 1; 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 = 0;
        while(s.find(record[i]) == s.end()){
            i++;
        }
        cout<<record[i]<<endl;
    }
    return 0;
}