北邮 BOJ 117 Single Number

思路：

    两个set，就很简单。

解答:

package bupt;

import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;

/*
*@author:Totoro
*@createDate:2020年3月16日下午4:08:00
*/
public class SingleNumber
	{

	public static void main(String[] args)
		{
		Scanner cin=new Scanner(System.in);
		Set<String> set1=new HashSet<>();
		Set<String> set2=new HashSet<>();
		while(cin.hasNext())
			{
			int N;
			N=cin.nextInt();
			cin.nextLine();
			String num;
			set1.clear();
			set2.clear();
			while(N--!=0)
				{
				num=cin.next();
				if(set2.contains(num))
					set2.remove(num);
				else if(set1.contains(num))
						{
						set1.remove(num);
						set2.add(num);
						}
				else
					set1.add(num);
				}
			String ans=set1.toString();
			ans=ans.substring(1,ans.length()-1);
			System.out.println(ans);
			}
		}

	}