Submission #162933

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Source Code Expand

import Control.Applicative
import Control.Monad
import Data.List

main = do
  [a , b] <- words <$> getLine
  putStrLn . show $ ( calc_keta b 0 - calc_keta (show ((read a) - 1)) 0 )

calc_keta :: String -> Integer -> Integer
calc_keta [] _      = 0
calc_keta (x:xs) n  = if n == read [x]
                          then if n == 4 || n == 9
                              then if length xs == 0 then 1 else ( read xs + 1 )
                              else calc_keta xs 0
                          else if n == 4 || n == 9
                              then 10 ^ ( length (x:xs) - 1 )    + calc_keta (x:xs) (n+1)
                              else keta_sum ( length(x:xs) - 1 ) + calc_keta (x:xs) (n+1)
         
keta_sum :: Int -> Integer
keta_sum 0 = 0
keta_sum x = 8 * keta_sum (x-1) + 2 * ( 10 ^ (x-1) )

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