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.

7 5 31 5 88 67 88 17

31

5 888 666 666 888 888

None

思路
和1084差不多的思路，队列q记录顺序，字典dic记录是否重复出现。遍历q的时候查下字典，输出第一个满足"仅出现一次"的数字即可。
代码

#include<iostream>
#include<map>
#include<iterator>
#include<queue>
using namespace std;
int main()
{
   int N;
   while(cin >> N)
   {
       map<int,int> dic;
       queue<int> q;
       for(int i = 0;i < N;i++)
       {
           int value;
           cin >> value;
           if(dic.count(value) > 0)
             dic[value] = -1;
           else
           {
              q.push(value);
              dic.insert(pair<int,int>(value,1));
           }
       }

       bool check = false;
       while(!q.empty())
       {
           if(dic[q.front()] > 0)
           {
             check = true;
             cout << q.front();
             break;
           }
           q.pop();
       }
       if(!check)
         cout << "None" << endl;
   }
}