# Haskell Quiz/The Solitaire Cipher/Solution Thiago Arrais

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< Haskell Quiz | The Solitaire Cipher(Difference between revisions)

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## Revision as of 18:02, 30 October 2007

module Main where import Char(chr, isAlpha, ord, toUpper) import List(intersperse) import System.Environment(getArgs, getProgName) toUpperCase = map toUpper toLetter n = chr $ ord 'A' + (n - 1) `mod` 26 toNumber l = ord l - ord 'A' + 1 split5 cs | length cs > 5 = (take 5 cs) : split5 (drop 5 cs) | otherwise = [cs] fill cs = cs ++ replicate (5 - length cs) 'X' -- Filters alpha characters and splits them into groups of five sanitize:: String -> [String] sanitize cs = reverse $ (fill.head) rchunks : tail rchunks where rchunks = reverse.split5.filter isAlpha.toUpperCase $ cs unkeyeddeck :: [Int] unkeyeddeck = [1..54] jokerA = 53 jokerB = 54 isJoker = (flip elem) [jokerA, jokerB] -- Pushes a card (j) down once push' j xs = if length right > 0 then left ++ head right : j : tail right else head left : j : tail left where (left,_:right) = break (== j) xs -- Pushes a card (j) down a given number (n) of times push j n = (!! n) . iterate (push' j) pushJokerA = push jokerA 1 pushJokerB = push jokerB 2 -- Performs a triplecut around the first two cards that satisfy a predicate (p) tripleCut p xs = bottom ++ j1 : (middle ++ j2 : top) where (top,j1:b1) = break p xs (middle,j2:bottom) = break p b1 countCut n xs = (reverse.tail $ rbottom) ++ top ++ [head rbottom] where top = take n xs rbottom = reverse.drop n $ xs -- Performs a count cut by the number written on the bottom card deckCut xs = countCut (last xs) xs valueFor 54 = 53 -- B joker's value is 53 valueFor n = n -- Shuffles the deck once nextDeck = deckCut.tripleCut isJoker.pushJokerB.pushJokerA -- Shuffles the deck once and extracts the resulting letter stepStream :: (String, [Int]) -> (String, [Int]) stepStream (_, oldDeck) = (letter $ number newDeck, newDeck) where newDeck = nextDeck oldDeck number deck@(n:_) = deck !! valueFor n letter n = if isJoker n then "" else toLetter n : [] -- The keystream generated by an unkeyed deck keystream = concat [c | (c,_) <- tail $ iterate stepStream ([], unkeyeddeck)] join = concat.intersperse " " -- Combines an input string (xs) and the default keystream by applying the -- given operation (f). This is the function that does the encoding/decoding codeWith f xs = join.sanitize.letterize $ zipWith f (numberize letters) (numberize keyletters) where keyletters = take (length letters) keystream numberize = map toNumber letterize = map toLetter letters = concat $ sanitize xs encode, decode :: String -> String encode = codeWith (+) decode = codeWith (-) -- An action that applies the coding function (f) to a set of words -- and prints the resulting code printCode f = putStrLn . f . join main = do args <- getArgs case args of ("d":ws@(_:_)) -> printCode decode ws ("e":ws@(_:_)) -> printCode encode ws _ -> getProgName >>= \n -> putStrLn $ "Usage: " ++ n ++ " <d/e> <phrase>"