Problem:
Score : 200 points

Problem Statement

You are given a string S consisting of lowercase English letters. Determine whether all the characters in S are different.

Constraints

2 ≤ |S| ≤ 26, where |S| denotes the length of S.

S consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:

S

Output

If all the characters in S are different, print yes (case-sensitive); otherwise, print no.

Sample Input 1

uncopyrightable

Sample Output 1

yes

Sample Input 2

different

Sample Output 2

no

Sample Input 3

no

Sample Output 3

yes

Solution in Haskell (GHC 7.10.3) (judge verdict: Accepted)

import qualified Data.ByteString.Char8 as BS
import Data.Maybe

readString = map BS.unpack . BS.words

getString = readString <$> BS.getLine

seek :: String -> Bool
seek [s] = True
seek (s : ss)
  | s `elem` ss = False
  | otherwise = seek ss

main = do
  [s] <- getString
  if seek s
    then putStrLn "yes"
    else putStrLn "no"