# Haskell Quiz/The Solitaire Cipher/Solution Paul

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## Latest revision as of 19:33, 21 February 2010

-- Solution to Ruby Quiz problem #1 -- Paul Brown (paulrbrown@gmail.com) -- http://mult.ifario.us/ import Char import List import Maybe to_number :: Char -> Int to_number c = fromEnum c - fromEnum 'A' + 1 from_number :: Int -> Char from_number n = toEnum (n - 1 + fromEnum 'A') to_numbers :: String -> [Int] to_numbers = map to_number cleanse :: String -> String cleanse = map toUpper . filter isAlpha pad :: Int -> Char -> String -> String pad n c s | length s < n = s ++ replicate (n-length s) c pad n c s | otherwise = s maybe_split :: String -> Maybe(String,String) maybe_split [] = Nothing maybe_split s | w == "" = Just (pad 5 'X' s,w) | otherwise = Just (take 5 s, w) where w = drop 5 s quintets :: String -> [String] quintets = unfoldr maybe_split data Suit = Clubs | Diamonds | Hearts | Spades | A | B deriving (Enum, Show, Bounded, Eq) show_suit :: Suit -> String show_suit = head . show data Face = Ace | Two | Three | Four | Five | Six | Seven | Eight | Nine | Ten | Jack | Queen | King | Joker deriving (Enum, Show, Bounded, Eq) show_face :: Face -> String show_face f = ["A23456789TJQK$" !! fromEnum f] data Card = Cd {suit :: Suit, face :: Face} deriving Eq instance Enum Card where toEnum 53 = Cd B Joker toEnum 52 = Cd A Joker toEnum n = let (q,r) = n `divMod` 13 in Cd (toEnum q) (toEnum r) fromEnum (Cd B Joker) = 53 fromEnum (Cd A Joker) = 52 fromEnum c = 13* fromEnum(suit c) + fromEnum(face c) instance Show Card where show c = show_face (face c) ++ show_suit (suit c) value :: Card -> Int value (Cd B Joker) = 53 value c = fromEnum c + 1 split_on_elem :: Eq a => a -> [a] -> ([a],[a]) split_on_elem x l | x == head l = ([],tail l) split_on_elem x l | x == last l = (init l, []) split_on_elem x l | otherwise = case elemIndex x l of Nothing -> error "Can't split a list on an element that isn't present." Just y -> (take y l, drop (y+1) l) swap_down :: Card -> [Card] -> [Card] swap_down x deck | null xs = head ys:x:tail ys | null ys = head xs:x:tail xs | otherwise = xs ++ (head ys:x:tail ys) where (xs,ys) = split_on_elem x deck move_a :: [Card] -> [Card] move_a deck = swap_down (Cd A Joker) deck move_b :: [Card] -> [Card] move_b deck = swap_down (Cd B Joker) (swap_down (Cd B Joker) deck) from_m_to_n :: Int -> Int -> [a] -> [a] from_m_to_n m n l | m < n = take (n-m-1) (drop (m+1) l) | n < m = take (m-n-1) (drop (n+1) l) triple_cut :: Card -> Card -> [Card] -> [Card] triple_cut x y deck | slot_x < slot_y = y2 ++ (x:(from_m_to_n slot_x slot_y deck)) ++ (y:x1) | slot_x > slot_y = x2 ++ (y:(from_m_to_n slot_y slot_x deck)) ++ (x:y1) where Just slot_x = elemIndex x deck Just slot_y = elemIndex y deck (x1,x2) = split_on_elem x deck (y1,y2) = split_on_elem y deck triple_cut_a_b :: [Card] -> [Card] triple_cut_a_b deck = triple_cut (Cd A Joker) (Cd B Joker) deck count_cut :: [Card] -> [Card] count_cut deck = drop (val-1) deck ++ take val deck ++ [bottom_card] where bottom_card = last deck val = value (bottom_card) evaluate :: [Card] -> Int evaluate deck = value (deck !! value (head deck)) compute :: [Card] -> (Int,[Card]) compute deck | val == 53 = compute x | otherwise = (val `mod` 26, x) where x = count_cut $ triple_cut_a_b $ move_b $ move_a $ deck val = evaluate x encode :: String -> String encode s = encode_ (concat (quintets (cleanse s))) [(Cd Clubs Ace) .. (Cd B Joker)] encode_ :: String -> [Card] -> String encode_ [] _ = [] encode_ (s:ss) deck = let (a,b) = compute deck in from_number(wrap_zero ((a + to_number s) `mod` 26)):encode_ ss b decode :: String -> String decode s = decode_ s [(Cd Clubs Ace) .. (Cd B Joker)] decode_ :: String -> [Card] -> String decode_ [] _ = [] decode_ (s:ss) deck = let (a,b) = compute deck in from_number(wrap_zero ((26 + to_number s - a) `mod` 26)):decode_ ss b wrap_zero :: Int -> Int wrap_zero 0 = 26 wrap_zero x = x