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;
namespace ABC154C
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            int[] a = Array.ConvertAll(Console.ReadLine().Split(' '), int.Parse);
            HashSet<int> dic = new HashSet<int>();
            string res = "YES";
            foreach (var item in a)
            {
                if (!dic.Add(item))
                {
                    res = "NO";
                    break;
                }
            }
            Console.WriteLine(res);
        }
    }
}