集合
序列中整数去重
http://www.nowcoder.com/questionTerminal/6564a2f6e70f4153ad1ffd58b2b28490
集合运算：
import java.util.*;
public class Main {
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
int N = sc.nextInt();
Set<Integer> s = new HashSet<>();
while (sc.hasNext()){
int n = sc.nextInt();
if(s.contains(n)) continue;
s.add(n);
System.out.printf("%d ", n);
}
}
}
