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.Text;
using System.Linq;

namespace at_coder
{
#if TEST
    [TestClass]
#endif
    public class abc154_c
    {

#if TEST
        public static void Test_Main()
#else
        public static void Main()
#endif
        {
            int N = readint();
            int[]A = ReadIntArray();

            HashSet<int> s = new HashSet<int>();
            int ngCount = 0;
            foreach(int i in A)
            {
                if (s.Contains(i))
                {
                    ngCount = 1;
                    break;
                }
                s.Add(i);
            }
            if (ngCount > 0)
            {
                println("NO");
            }
            else
            {
                println("YES");
            }
        }

        private static void println(string s)
        {
            Console.WriteLine(s);
        }

        private static int readint()
        {
            String s = Console.ReadLine();
            return int.Parse(s);
        }

        private static int[] ReadIntArray()
        {
            string[] ss = Console.ReadLine().Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
            int[] ar = new int[ss.Length];
            for (int i = 0; i < ss.Length; i++)
            {
                ar[i] = int.Parse(ss[i]);
            }
            return ar;
        }

#if TEST
#else
    }
}
#endif