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 7.10.3) (judge verdict: Accepted)

import qualified Data.IntSet as S
  
main :: IO ()
main = do
  getLine
  as <- map read . words <$> getLine
  putStrLn $ if (solve as) then "YES" else "NO"

solve :: [Int] -> Bool
solve as = go S.empty as
  where
    go _ [] = True
    go s (a:as)
      | a `S.member` s = False
      | otherwise      = go (S.insert a s) as