# Haskell Quiz/The Solitaire Cipher/Solution Paul

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## Revision as of 11:00, 13 January 2007

-- 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 s = map to_number s cleanse :: String -> String cleanse c = (map toUpper) ((filter isAlpha) c) pad :: Int -> Char -> String -> String pad n c s | length s < n = s ++ (replicate (n-length s) c) pad n c s = s maybe_split :: String -> Maybe(String,String) maybe_split [] = Nothing maybe_split s | w == "" = Just (pad 5 'X' s,w) | True = Just (take 5 s, w) where w = drop 5 s quintets :: String -> [String] quintets s = (unfoldr maybe_split) s data Suit = Clubs | Diamonds | Hearts | Spades | A | B deriving (Enum, Show, Bounded, Eq) show_suit :: Suit -> String show_suit s = (take 1) (show s) 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 = [head (drop (fromEnum f) "A23456789TJQK$")] data Card = Cd Suit Face deriving Eq suit :: Card -> Suit suit (Cd s _) = s face :: Card -> Face face (Cd _ f) = f instance Enum Card where toEnum 53 = (Cd B Joker) toEnum 52 = (Cd A Joker) toEnum n = let d = n `divMod` 13 in Cd (toEnum (fst d)) (toEnum (snd d)) 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 drop_tail :: [a] -> [a] drop_tail l = reverse (drop 1 (reverse l)) split_on_elem :: Eq a => a -> [a] -> ([a],[a]) split_on_elem x l | x == head l = ([],drop 1 l) split_on_elem x l | x == head (reverse l) = (drop_tail l, []) split_on_elem x l | elemIndex x l == Nothing = error "Can't split a list on an element that isn't present." split_on_elem x l = let y = fromJust(elemIndex x l) in (take y l, drop (y+1) l) swap_down :: Card -> [Card] -> [Card] swap_down x deck | (fst halves) == [] = (head (snd halves)):(x:(drop 1 (snd halves))) | (snd halves) == [] = (head (fst halves)):x:(drop 1 (fst halves)) | True = (fst halves) ++ ((head (snd halves)):x:(drop 1 (snd halves))) where halves = 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 = (snd (split_y)) ++ (x:(from_m_to_n slot_x slot_y deck)) ++ (y:(fst split_x)) | slot_x > slot_y = (snd (split_x)) ++ (y:(from_m_to_n slot_y slot_x deck)) ++ (x:(fst split_y)) where slot_x = fromJust(elemIndex x deck) slot_y = fromJust(elemIndex y deck) split_x = split_on_elem x deck split_y = 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_tail (drop val deck)) ++ (take val deck) ++ [bottom_card] where bottom_card = head (reverse deck) val = value (bottom_card) evaluate :: [Card] -> Int evaluate deck = value (head (drop (value(head(deck))) deck)) compute :: [Card] -> (Int,[Card]) compute deck | val == 53 = compute (x) | True = ((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 c = compute(deck) in (from_number(wrap_zero ((fst c + (to_number s)) `mod` 26))):(encode_ ss (snd c)) decode :: String -> String decode s = decode_ s [(Cd Clubs Ace) .. (Cd B Joker)] decode_ :: String -> [Card] -> String decode_ [] _ = [] decode_ (s:ss) deck = let c = compute(deck) in (from_number(wrap_zero ((26 + (to_number s) - fst c) `mod` 26))):(decode_ ss (snd c)) wrap_zero :: Int -> Int wrap_zero 0 = 26 wrap_zero x = x