PAT甲级A1041 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：给定n个数，让你找出其中第一个独一无二的数字（即第一个没有重复出现过的数字）输出， 如果没有则输出None。

思路：使用哈希表标记每个数字出现的次数，最后再顺序找出第一个哈希值为1的数字输出。

参考代码：

#include<cstdio>
#include<vector>
using namespace std;
int ht[10010];
int main()
{
	int n,t;
	scanf("%d",&n);
	vector<int> v;
	for(int i=0;i<n;i++){
		scanf("%d",&t);
		ht[t]++;
		v.push_back(t);
	}
	bool flag=false;
	for(int i=0;i<v.size()&&!flag;i++){
		if(ht[v[i]]==1){
			printf("%d\n",v[i]);
			flag=true;
		}	
	}
	if(!flag) printf("None\n");
	return 0;
}