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 Ruby (2.3.3) (judge verdict: Accepted)

# coding: utf-8
class Case03

  def initialize
  end

  def show
    p self.instance_variables
        .map{ |sym| [sym, self.instance_variable_get(sym)] }
        .to_h
  end
  
  # 実行する
  def execute
    read
    solve
    output
  end

  def read
    @n = gets.chomp.to_i
    @a = gets.chomp.split.map(&:to_i)
  end

  def solve
    @a.sort!
    @result = 'YES'
    0.upto(@n-2) do |i|
      if @a[i] == @a[i+1] then
        @result = 'NO'
        break;
      end
    end
  end
  
  def output
    puts @result
  end

end

Case03.new.execute if $0 == __FILE__