PAT (Advanced Level) Practice 1041 Be Unique （20 分）

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 (≤10​5​​) 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

 题意：
找到第一个没有在序列中唯一的元素。

代码如下：

#include <bits/stdc++.h>
using namespace std;
const int maxn=1e5+5;
int a[maxn];
int n;
map<int,int>ma;
int main()
{
	scanf("%d",&n);
	for (int i=0;i<n;i++)
	{
		scanf("%d",&a[i]);
		ma[a[i]]++;
	}
	int flag=0;
	for (int i;i<n;i++)
	{
		if(ma[a[i]]==1)
		{
			flag=1;
			printf("%d\n",a[i]);
			break;
		}
	}
	if(!flag)
	{
		printf("None\n");
	}
	return 0;
}