【PAT（甲级）】1041 Be Unique

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 [1,104]. 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 (≤105) 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

解题思路：

题目要求的意思是找到给出数字中只出现过一次的数字，如果这种数字不止一个，则按照输入顺序，输出第一个只出现一次的数字。

这种问题就用map将数字和出现次数对应起来就可以了。然后再循环输入的数字，如果出现次数为1就直接输出。

易错点：

1. 要输出第一个只出现一次的数字

代码：

#include
using namespace std;
 
int main(){
	int N;
	cin>>N;
	map<int,int> number;
	int a[N];
	for(int i=0;i
		cin>>a[i];
		number[a[i]]++;
	}
	for(int i=0;i!=N;i++){
		if(number[a[i]]==1){
			cout<
			return 0;
		}
	}
	cout<<"None";
	return 0;
}