A1041 Be Unique [哈希]

#include<iostream>
#include<vector>
#include<queue>
#include<stack>
#include<string>
#include<math.h>
#include<algorithm>
#include<map>
#include<cstring>
#include<set>
using namespace std;
const int maxn = 100001;
int hashtable[maxn],a[maxn];
int main()
{
	int n,x; cin >> n;
	for (int i = 0; i < n; i++)
	{
		cin >> a[i];
		hashtable[a[i]]++;
	}
	for (int i = 0; i < maxn; i++)
	{
		if (hashtable[a[i]] == 1)
		{
			cout << a[i];
			return 0;
		}
	}
	cout << "None" << endl;
}