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;
 
public class B {
    public static void Main(){
        string line = Console.ReadLine();
        int N = int.Parse(line);
        string[] lines = Console.ReadLine().Split(' ');
        List<long> A = new List<long>();
        // リストの構築
        for (int i=0;i<lines.Length;i++)
        {
            A.Add(long.Parse(lines[i]));
        }
        
        bool isDif = false;
        while (A.Count > 0)
        {
            long target = A[0];
            A.RemoveAt(0);
            if (A.IndexOf(target)>=0)
            {
                Console.WriteLine("NO");
                isDif = true;
                break;
            }
        }
        if (!isDif)
        {
            Console.WriteLine("YES");
        }
    }
}