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 Java7 (OpenJDK 1.7.0) (judge verdict: Wrong Answer)

import java.util.HashMap;
import java.util.Scanner;
 
public class Main {
	public static void main(String[] args) {
 
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		String anser = "YES";
 
		HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
 
		for (int i = 0; i < N; i++) {
			map.put(scan.nextInt(), i);
		}
 
		for (int i = 0; i < N; i++) {
			int size = map.size();
			map.remove(map.get(i));
 
			if (size - 1 > map.size()) {
				anser = "NO";
				break;
			}
		}
		System.out.println(anser);
	}
 
}