PAT-A1041 Be Unique【散列】

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

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实际上是数组散列的过程，输出第一个不重复的数字。使用map记录每个数字的重复次数，vector保存序列，然后从前往后遍历。

#include <iostream>
#include <vector>
#include <map>
using namespace std;
int main(){
	int n;
	scanf("%d",&n);
	int temp;
	map<int,int> time;
	vector<int> seq;
	while(n--){
		scanf("%d",&temp);
		time[temp]++;
		seq.push_back(temp);
	}
	int num=-1;
	for(int i=0;i<seq.size();i++){
		if(time[seq[i]]==1){
			num=seq[i];
			break;
		}
	}
	if(num==-1){
		cout<<"None";
	}
	else{
		cout<<num;
	}
return 0;
}