Problem:
Score : 300 points

Problem Statement

Given is a sequence of integers A_1, A_2, ..., A_N.
If its elements are pairwise distinct, print YES; otherwise, print NO.

Constraints

2 ≤ N ≤ 200000

1 ≤ A_i ≤ 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 ... A_N

Output

If the elements of the sequence are pairwise distinct, print YES; otherwise, print NO.

Sample Input 1

5
2 6 1 4 5

Sample Output 1

YES

The elements are pairwise distinct.

Sample Input 2

6
4 1 3 1 6 2

Sample Output 2

NO

The second and fourth elements are identical.

Sample Input 3

2
10000000 10000000

Sample Output 3

NO

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;
import java.util.PriorityQueue;

class Main{
  public static void main(String[] args){
    Scanner scan=new Scanner(System.in);
    int num=scan.nextInt();
    boolean flag=true;
    PriorityQueue in=new PriorityQueue();
    for(int x=0; x<num; x++){
      int input=scan.nextInt();
      in.offer(input);
    }
    int before=(int)in.poll();
    int after;
    for(int x=1; x<num; x++){
      after=(int)in.poll();
      if(before==after){
        flag=false;
        break;
      }else{
        before=after;
      }
    }
    if(flag){
      System.out.println("YES");
    }else{
      System.out.println("NO");
    }
  }
}