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: Time Limit Exceeded)

N = gets.chomp.to_i
A = gets.split(" ").map(&:to_i)

res = false
a = A.dup

N.times do |i|
  s = a.delete_at(i)
  
  if a.size == 1
    res = true if a.include?(s)
    break
  end

  slice_size = (N < 10000) ? (a.size / 2) : 10000

  a.each_slice(slice_size) do |l|
    if l.include?(s)
      res = true
      break
    end
  end

  a = A.dup
end

puts res ? "NO" : "YES"