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: Time Limit Exceeded)

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    public static void Main()
    {
        int N = int.Parse(Console.ReadLine());
        string []input=Console.ReadLine().Split();
        int []A = new int[N];
        string flag = "YES";
        A[0] = int.Parse(input[0]);
        for (int i = 1; i < N; i++)
        {
            A[i] = int.Parse(input[i]);
            for(int j = i-1; j >= 0; j--)
            {
                if (A[i] == A[j]) { flag = "NO"; }
            }
        }
        Console.WriteLine(flag);
    }
}