Intercalación de n copias
Enunciado
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-- Definir la función -- intercala :: Int -> a -> [a] -> [[a]] -- tal que (intercala n x ys) es la lista de la listas obtenidas -- intercalando n copias de x en ys. Por ejemplo, -- intercala 2 'a' "bc" == ["bcaa","baca","baac","abca","abac","aabc"] -- intercala 2 'a' "c" == ["caa","aca","aac"] -- intercala 1 'a' "c" == ["ca","ac"] -- intercala 0 'a' "c" == ["c"] -- Nota: No importa el orden de los elementos. |
Soluciones
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import Data.List -- 1ª solución -- =========== intercala1 :: Int -> a -> [a] -> [[a]] intercala1 0 _ xs = [xs] intercala1 n y [] = [replicate n y] intercala1 n y (x:xs) = concat [[replicate i y ++ (x:zs) | zs <- intercala1 (n-i) y xs] | i <- [0..n]] -- 2ª solución -- =========== intercala2 :: Eq a => Int -> a -> [a] -> [[a]] intercala2 n x ys = nub (aux n x ys) where aux 0 _ ys = [ys] aux n x ys = concat [intercalaUno x zs | zs <- aux (n-1) x ys] -- intercalaUno 'a' "bc" == ["abc","bac","bca"] intercalaUno :: a -> [a] -> [[a]] intercalaUno x [] = [[x]] intercalaUno x (y:ys) = (x:y:ys) : [y:zs | zs <- intercalaUno x ys] |