1041 Be Unique (20 point(s))

1041 Be Unique (20 point(s))

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

 简单题。这种限制输入数字范围的往往都是要用到Hash思想。思考：可否只在输入时候处理，不存储和扫描元素？

#include<iostream>
using namespace std;
const int N = 1e4+1;
const int M = 1e5+7;
int cnt[N]={0};
int a[M];
int main(void)
{
	int n;cin>>n;
	for(int i=0;i<n;i++){
		cin>>a[i];cnt[a[i]]++;
	}
	int ans = -1;
	for(int i=0;i<n;i++){
		if(cnt[a[i]]==1){
			ans = a[i];break;
		}
	}
	if(ans==-1) cout<<"None"<<endl;
	else cout<<ans<<endl;
	return 0;
}