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: Wrong Answer)

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

a = A.dup.sort

res = false

head = 0
tail = a.size - 2

N.times do |n|
  t = a.delete_at(head)
  while head < tail
    center = (head + tail) / 2

    if a[center] == t
      res = true
      break
    elsif a[center] < t
      head = center + 1
    else
      tail = center - 1
    end
  end  
end

puts res ? "NO" : "YES"