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 MyProgram{
    class AtCoder{
        static void Main(){
            var N = long.Parse(Console.ReadLine());
            var A = Array.ConvertAll(Console.ReadLine().Split(' '),long.Parse);
            var dict = new Dictionary<long,long>();
            for(var i=0;i<N;i++){
                if(!dict.ContainsKey(A[i]))dict[A[i]] = 0;
                else{
                    Console.WriteLine("NO");
                    return;
                }
            }
            Console.WriteLine("YES");
        }
    }
}