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.Linq;

public class AtCoder_154_C
{
    public static void Main()
    {
        //var exStdIn = new System.IO.StreamReader( "input.txt" );
        //System.Console.SetIn( exStdIn );

        int n = int.Parse(Console.ReadLine());
        int[] A = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();

        bool[] array = new bool[1001001001];

        for (int i = 0; i < n; i++)
        {
            if (array[A[i]])
            {
                Console.WriteLine("NO");
                return;
            }
            array[A[i]] = true;
        }

        Console.WriteLine("YES");
    }
}