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 static System.Console;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;

namespace Atcoder_Answer
{
    class Program
    {
        const int mod = 1000000007;

        static void Main(string[] args)
        {
            int N = int.Parse(ReadLine());
            string[] Reader = ReadLine().Split(' ');
            int[] As = Reader.Select(int.Parse).ToArray();
            List<int> ABody = new List<int>();
            ABody.AddRange(As);

            ABody.Sort((a, b) => a - b);

            bool Ret = true;
            for (int loop = 0; loop < N - 1; loop++) 
            {
                if (ABody[loop] == ABody[loop + 1]) 
                {
                    Ret = false;
                    break;
                }
            }

            if (Ret) WriteLine("YES");
            else WriteLine("NO");
        }

    }

    public static class Extension
    {
        #region 拡張:bool
        #region キャスト関連
        public static int ToInt(this bool Bool)
        {
            if (Bool) return 1;
            else return 0;
        }

        public static string ToString(this bool Bool, string TrueStr, string FalseStr)
        {
            if (Bool) return TrueStr;
            else return FalseStr;
        }
        #endregion
        #endregion

        #region 拡張:int
        #region キャスト関連
        public static char ToAlphaBets(this int Base) => (char)Base;
        #endregion
        #endregion

        #region 拡張:char
        #region 変換関連
        public static char NextAlpha(this char Char) => (char)((Char) + 1); //次の文字を取得
        #endregion
        #endregion

        #region 拡張:int[]
        public static long Sum(this int[] Array)
        {
            int Ret = 0;
            for (int loop = 0; loop < Array.Length; loop++) Ret += Array[loop];
            return Ret;
        }
        #endregion

        #region 拡張: string
        public static string Multi(this string THIS, int Value) 
        {
            string RetValue = "";

            for (int loop = 0; loop < Value; loop++) RetValue += THIS;

            return RetValue;
        }
        #endregion
    }
}