题目来源：http://codeup.cn/problem.php?cid=100000582&pid=2

感谢晴神的《算法笔记》

题目描述

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.

输入

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.

输出

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

样例输入

7 5 31 5 88 67 88 17
5 888 666 666 888 888

样例输出

31
None

#include <iostream>
#include <cstring>
#include <fstream>
#include <string>
#include <cmath>
#include <algorithm>
#include <queue>
#include <set>
#include <map>

using namespace std;

void clear(queue<int>& q) {
    queue<int> empty;
    swap(empty, q);
}

int main()
{
    queue<int> unique;
    set<int> list_1,list_2;
    int N;
    while(cin>>N){
        while(N--){
            int t;
            cin>>t;
            if((!unique.empty()) && unique.front()==t){
                unique.pop();
                while((!unique.empty()) && list_2.find(unique.front())!=list_2.end())
                    unique.pop();
            }
            if(list_1.find(t)!=list_1.end()){
                list_2.insert(t);
            }
            else {
                list_1.insert(t);
                unique.push(t);
            }
        }
        if(unique.empty())
            cout<<"None"<<endl;
        else
            cout<<unique.front()<<endl;
        list_1.clear();
        list_2.clear();
        clear(unique);
    }
    return 0;
}