PATA1041题解

#include<iostream>
#include<vector>
#include<algorithm>
#include<cstring>
#include<map>
#include<set>
#include<cstring>
#include<stdio.h>
#include<queue>
using namespace std;
char ch[5000];
int len;
int main() {
    map<int, int> mp;
    vector<int>vec;
    int N, number;
    cin >> N;
    for(int i = 0; i < N; i++) {
        cin>>number;
        if(mp.find(number) == mp.end()) {
            vec.push_back(number);
        }else {
            vector<int>::iterator it = vec.begin() ;
                while(it != vec.end()) {
                    if(*it == number) {
                        vec.erase(it);
                        break;
                    }
                    it++;
                }
            
            }
        mp[number]++;
    } 
    if(vec.size() == 0) cout << "None";
    else cout << vec[0];
}