# Haskell Quiz/The Solitaire Cipher/Solution JFoutz

From HaskellWiki

This took longer than expected. I didn't read the specification closely enough to realize both jokers count as 53 rather than A == 53 and B == 54

Other than that, looking through Data.List for shortcuts was educational. I really like zipWith and groupBy.

This could probably use a lot more orginization, and a bit more commentary. Fortunately the function names match the spec closely, which helps.

```
import Data.Char
import Data.List
import System
-- discard any non a to z characers, uppercase the rest
-- split into groups of 5, padded with 'X'
prep ls = loop $ map toUpper $ filter (\x -> and [isAscii x, isLetter x]) ls
where loop [] = []
loop ls
| length ls < 5 = [take 5 (ls ++ "XXXX")]
| otherwise = (take 5 ls) : loop (drop 5 ls)
drawMsg msg = unwords (loop msg)
where loop msg
| length msg > 5 = (take 5 msg) : loop (drop 5 msg)
| otherwise = [msg]
churn f msg = drawMsg $ toChr $ zipWith f (toNum $ concat $ prep msg) (keyStream [1..54])
crypt msg = churn solAdd msg
decrypt msg = churn solSub msg
main = do (x:xs) <- getArgs
case x of
"c" -> putStrLn $ crypt $ concat $ xs
"d" -> putStrLn $ decrypt $ concat $ xs
_ -> putStrLn "Try solitaire c my message, or d my message"}
-- letters to numbers and back
toNum = map (\x -> ord x - 65)
toChr = map (\x -> chr (x + 65))
-- add and subtract base solitaire style
solAdd x y = (x + y) `mod` 26
solSub x y = (x + 26 - y) `mod` 26
--keyStream
down1 x ls = move $ break (==x) ls
where move (x:xs, t:[]) = x:t:xs
move (xs, c:n:cx) = xs ++ n : c : cx
down2 x ls = down1 x $ down1 x ls
notEither a b = (\x y -> x /= a && y /= a && x /= b && y /= b)
tripleCut a b ls = swap a b $ concat $ reverse $ groupBy (notEither a b) ls
swap a b [] = []
swap a b (x:xs)
| a == x = b : swap a b xs
| b == x = a : swap a b xs
| otherwise = x : swap a b xs
cardVal c = if c == 54 then 53 else c
countCut ls = glue $ splitAt (cardVal $ last ls) (init ls)
where glue (f,b) = b ++ f ++ [last ls]
jokerA = 53
jokerB = 54
keyStep deck = countCut $ tripleCut jokerA jokerB $ down2 jokerB $ down1 jokerA deck
getCard deck = deck !! (cardVal $ head deck)
keyStream deck = let d2 = keyStep deck
out = getCard d2
in if out == jokerA || out == jokerB
then keyStream d2
else out : keyStream d2
```