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 DistinctOrNot
{
    static void Main(string[] args)
    {
        var times = int.Parse(Console.ReadLine());
        var input = Console.ReadLine().Split(' ');
        var output = "YES";

        var hashset = new HashSet<string>();

        foreach (var i in input)
        {
            // 既に追加済みのキーが来た場合はfalseになる
            if (!hashset.Add(i))
            {
                output = "NO";
                break;
            }
        }

        Console.WriteLine(output);
    }
}