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: Wrong Answer)

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {
	public static void main (String args[]) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		Map<Long, Integer> map = new HashMap<Long, Integer>();
		for(int i = 0; i < n;i++){
			long a = scan.nextLong();
			if(map.get(a) == null) {
				map.put(a, 0);
			} else {
				System.out.println("YES");
				return;
			}
		}
		System.out.println("NO");
	}
}