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.Collections.Generic;
using System.Linq;

public class Hello
{
    public static void Main()
    {
        hoge();
        System.Console.ReadLine();
    }

    public static void hoge()
    {
        var n = int.Parse(System.Console.ReadLine());
        var nums = System.Console.ReadLine().Split(' ').Select(long.Parse);

        Dictionary<long, int> dic = new Dictionary<long, int>();

        foreach(var num in nums)
        {
            if (dic.ContainsKey(num))
            {
                System.Console.WriteLine("NO");
                return;
            }
            dic.Add(num, 0);
        }
        System.Console.WriteLine("YES");
    }


}