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 AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            //[summary]C - Distinct or Not
            if (IsDoubled())
            {
                Console.WriteLine("YES");
            }
            else
            {
                Console.WriteLine("NO");
            }            
        }

        static bool IsDoubled()
        {
            int N = int.Parse(Console.ReadLine());
            var A = ReadLine();

            var dic = new Dictionary<int, int>();

            foreach (var a in A)
            {
                if (dic.ContainsKey(a))
                {
                    return false;
                }
                else
                {
                    dic.Add(a, 1);
                }
            }

            return true;
        }

        static List<int> ReadLine()
        {
            var line = Console.ReadLine();
            var arr = line.Split(' ');

            return arr.Select(x => int.Parse(x)).ToList();
        }
    }
}