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;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AtCoder.Abc
{
    class QuestionC
    {
        public static void Main(string[] args)
        {
            var sw = new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            Console.SetOut(sw);
            
            // 整数の入力
            long n = long.Parse(Console.ReadLine());

            // 整数配列の入力
            var aArray = Console.ReadLine().Split(' ').Select(i => long.Parse(i)).ToArray();

            HashSet<long> set = new HashSet<long>();

            for(int i = 0; i < n; i++)
            {
                long a = aArray[i];
                if (set.Contains(a))
                {
                    Console.WriteLine("NO");
                    Console.Out.Flush();
                    return;
                }
                set.Add(a);
            }

            Console.WriteLine("YES");

            Console.Out.Flush();
        }
    }
}