Code Jam 2012 Qualification

a.hs

import qualified Data.Map as M

subst = [('a','y'),('b','n'),
         ('c','f'),('d','i'),
         ('e','c'),('f','w'),
         ('g','l'),('h','b'),
         ('i','k'),('j','u'),
         ('k','o'),('l','m'),
         ('m','x'),('n','s'),
         ('o','e'),('p','v'),
         ('q','z'),('r','p'),
         ('s','d'),('t','r'),
         ('u','j'),('v','g'),
         ('w','t'),('x','h'),
         ('y','a'),('z','q')]

substTo = M.fromList subst
substFrom = M.fromList $ map (\(a, b) -> (b, a)) subst

crypt t s = zipWith join s new
  where 
    new = map (\x -> M.lookup x t) s
    join a Nothing = a
    join a (Just b) = b

encrypt = crypt substTo
decrypt = crypt substFrom

solveFile s = concat . map (\(n,s) -> "Case #"++show n++": "++s++"\n") $ l
  where
    n = (read . head . lines $ s) :: Int
    l = zip [1..] $ map decrypt (take n . drop 1 . lines $ s)
  
main = interact solveFile

c.hs

import Data.List

-- All distinct pairs
generate a b = [(x, y) | x <- [a..b], y <- [a..b], x < y]

-- Is pair recycled?
test (a,b) = length sa == length sb && isShift sa sb 
  where 
    sa = show a
    sb = show b 
    isShift a b = any (isPrefixOf a) . take (length b) . tails . cycle $ b

-- Process input
solve s = unlines . cases . map (show . solveOne) $ tests
  where
    prep :: [[Int]]
    prep = map (map read . words) . lines $ s
    t = head . head $ prep
    tests = take t . drop 1 $ prep
    solveOne [a, b] = length . filter (\x->x) . map test $ generate a b
    cases cs = map (\(n,x) -> "Case #"++show n++": "++x) . zip [1..] $ cs

main = interact solve


-- vim: cindent

Бросается в глаза слабое знание стандартной библиотеки. К примеру, \x->x это id, \(a, b) -> (b, a) - Data.Tuple.swap, а concat . map (\(n,s) -> "Case #"++show n++": "++s++"\n") $ l просто (\(n,s) -> "Case #"++show n++": "++s++"\n") =<< l или даже (uncurry $ printf "Case #%d: %s\n") =<< l

Насчет слабого знания не могу не согласиться --- практики работы с языком маловато. За практический пример использования list monad отдельное спасибо.