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;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using static System.Console;
using static System.Math;

namespace AtCoder
{
  public class Program
  {
    public static void Main(string[] args)
    {
      new Program().Solve(new ConsoleInput(Console.In, ' '));
    }
    public void Solve(ConsoleInput cin)
    {
      var n = cin.ReadInt;
      var sequence = cin.ReadIntArray(n);
      int distinctCount = (from x in sequence select x).Distinct().Count();
      if (n == distinctCount)
      {
        WriteLine("YES");
      }
      else
      {
        WriteLine("NO");
      }
    }
  }

  public class ConsoleInput
  {
    private readonly System.IO.TextReader _stream;
    private char _separator = ' ';
    private Queue<string> inputStream;
    public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
    {
      this._separator = separator;
      this._stream = stream;
      inputStream = new Queue<string>();
    }
    public string Read
    {
      get
      {
        if (inputStream.Count != 0) return inputStream.Dequeue();
        string[] tmp = _stream.ReadLine().Split(_separator);
        for (int i = 0; i < tmp.Length; ++i)
          inputStream.Enqueue(tmp[i]);
        return inputStream.Dequeue();
      }
    }
    public string ReadLine { get { return _stream.ReadLine(); } }
    public int ReadInt { get { return int.Parse(Read); } }
    public long ReadLong { get { return long.Parse(Read); } }
    public double ReadDouble { get { return double.Parse(Read); } }
    public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret; }
    public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
    public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }
  }
}