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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
	{
		Console.ReadLine();
		var a = Array.ConvertAll(Console.ReadLine().Split(new[] { ' ' }), number => int.Parse(number));

		var dictionary = new Dictionary<int, int>();

		var contains = false;
		for (var i = 0; i < a.Length && !contains; ++i) {
			if (dictionary.ContainsKey(a[i])) {
				contains = true;
			} else {
				dictionary.Add(a[i], 0);
			}
		}

		Console.WriteLine(contains ? "NO" : "YES");
	}
}