A1041 Be Unique (20 point(s))

寻找只出现一次的数

1. 原文

原题

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

2. 解析

输出仅出现一次的数

3. AC代码

#include<cstdio>
#include<map>
using namespace std;
map<int,int> exist;
int num[100010]={};
int main()
{
	int n;
	scanf("%d",&n);
	for (int i = 0; i < n; ++i)
	{
		scanf("%d",&num[i]);
		exist[num[i]]++;
	}
	int flag=0;
	for (int i = 0; i < n; ++i)
	{
		if (exist[num[i]]==1)
		{
			flag=1;
			printf("%d\n", num[i]);
			break;
		}
	}
	if (flag==0)
	{
		printf("None\n");
	}
	return 0;
}