gistfile1.lhs

import Data.List (sortBy)

data Op = UP | DN deriving (Show, Eq)

serie :: Integer -> [Op]
serie 1 = cycle [UP,DN]
serie x 
    | odd x = UP : (serie (div ((3*x)+1) 2))
    | even x = DN : (serie (div x 2))

serie_a_entero :: [Op] -> Integer
serie_a_entero xs = sum $ zipWith (\ j k -> if j == UP then k else 0) xs (map (2^) [0..])

-- el nivel n en el árbol de congruencias
nivel :: Integer -> [Integer]
nivel n = reordena xs where
    xs = 0 : map (serie_a_entero.reverse.(take $ fromInteger n).serie) [1..((2^n)-1)]
    reordena ys = map fst $ sortBy (\ j k -> compare (snd j) (snd k)) $ zip [0..] ys