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: Time Limit Exceeded)

using System;

public class Program {
  public static void Main(string[] args) {
    var str = Console.ReadLine();
    int n = int.Parse(str);
    int[] a = new int[n];
    var str2 = Console.ReadLine().Split();
    //int flag = 0;
    
    for (int i = 0; i < n; i++) {
      a[i] = int.Parse(str2[i]);
    }
    
    for (int i = 0; i < n; i++) {
      for (int j = i+1; j < n; j++) {
        if (a[i] == a[j]) {
          Console.WriteLine("NO");
          return ;
        }
      }
    }
          
    Console.WriteLine("YES");
  }
}