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.Linq;
using System.Collections.Generic;

class Program
{
	static void Main(string[] args)
	{			
		//文字列を読み込む
		int num = int.Parse(Console.ReadLine());
		string[] numbers = Console.ReadLine().Split(' ');
		
		//存在を判別するリストを定義
		List<string> existence = new List<string>();
		
		//判別する変数を定義
		bool distinct = true;
		
		for(int i=0; i<num; i++){
				string Ai = numbers[i];
				if(existence.Contains(Ai)){
						distinct = false;
						break;
				}else{
						existence.Add(Ai);
				}
		}
		
		//出力
		if(distinct){
				Console.WriteLine("YES");
		}else{
				Console.WriteLine("NO");
		}
	}
}