PAT Advanced 1041 Be Unique（20）

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 [1,10^4]. 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

题目大意：

给n个数字，按照读入顺序，哪个数字是第一个在所有数字中只出现一次的数字。如果所有数字出现都超过了一次，则输出None

#include<iostream>
using namespace std;

const int N = 100010;
int a[N], ha[N];
int n;

int main()
{
    cin >> n;
    for(int i = 0 ; i < n ; i ++)   
    {
        scanf("%d", &a[i]);
        ha[a[i]] ++;
    }
    
    bool flag = false;
    for(int i = 0 ; i < n ; i ++)
        if(ha[a[i]] == 1)
        {
            flag = true;
            cout << a[i];
            break;
        }
    if(!flag)   cout << "None";
    return 0;
}