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 Haskell (GHC 8.8.3) (judge verdict: Accepted)

import           Data.Set (empty, member, insert)

nub' :: (Ord a) => [a] -> [a]
nub' l = nub'' l empty
  where
    nub'' [] _ = []
    nub'' (x:xs) s
      | x `member` s = nub'' xs s
      | otherwise = x:nub'' xs (x `insert` s)

main = do
  getLine
  a <- map (read :: String -> Int) . words <$> getLine
  putStrLn
    $ if length a == (length . nub') a
      then "YES"
      else "NO"