Una palabra es una anagrama de otra si se puede obtener permutando sus letras. Por ejemplo, \u00abmora\u00bb y \u00abroma\u00bb son anagramas de \u00abamor\u00bb.<\/p>\n
Definir la funci\u00f3n<\/p>\n
\n anagramas :: String -> [String] -> [String]\n<\/pre>\ntal que (anagramas x ys) es la lista de los elementos de ys que son anagramas de x. Por ejemplo,<\/p>\n
\n \u03bb> anagramas \"amor\" [\"Roma\",\"mola\",\"loma\",\"moRa\", \"rama\"]\n [\"Roma\",\"moRa\"]\n \u03bb> anagramas \"rama\" [\"aMar\",\"amaRa\",\"roMa\",\"marr\",\"aRma\"]\n [\"aMar\",\"aRma\"]\n<\/pre>\nSoluciones<\/h4>\n\nimport Data.List (delete, permutations, sort)\nimport Data.Char (toLower)\nimport Data.Function (on)\n\n-- 1\u00aa soluci\u00f3n\n-- =============\n\nanagramas :: String -> [String] -> [String]\nanagramas _ [] = []\nanagramas x (y:ys)\n | sonAnagramas x y = y : anagramas x ys\n | otherwise = anagramas x ys\n\n-- (sonAnagramas xs ys) se verifica si xs e ys son anagramas. Por\n-- ejemplo,\n-- sonAnagramas \"amor\" \"Roma\" == True\n-- sonAnagramas \"amor\" \"mola\" == False\nsonAnagramas :: String -> String -> Bool\nsonAnagramas xs ys =\n sort (map toLower xs) == sort (map toLower ys)\n\n-- 2\u00aa soluci\u00f3n\n-- =============\n\nanagramas2 :: String -> [String] -> [String]\nanagramas2 _ [] = []\nanagramas2 x (y:ys)\n | sonAnagramas2 x y = y : anagramas2 x ys\n | otherwise = anagramas2 x ys\n\nsonAnagramas2 :: String -> String -> Bool\nsonAnagramas2 xs ys =\n (sort . map toLower) xs == (sort . map toLower) ys\n\n-- 3\u00aa soluci\u00f3n\n-- ===========\n\nanagramas3 :: String -> [String] -> [String]\nanagramas3 _ [] = []\nanagramas3 x (y:ys)\n | sonAnagramas3 x y = y : anagramas3 x ys\n | otherwise = anagramas3 x ys\n\nsonAnagramas3 :: String -> String -> Bool\nsonAnagramas3 = (==) `on` (sort . map toLower)\n\n-- Nota. En la soluci\u00f3n anterior se usa la funci\u00f3n on ya que\n-- (f `on` g) x y\n-- es equivalente a\n-- f (g x) (g y)\n-- Por ejemplo,\n-- \u03bb> ((*) `on` (+2)) 3 4\n-- 30\n\n-- 4\u00aa soluci\u00f3n\n-- ===========\n\nanagramas4 :: String -> [String] -> [String]\nanagramas4 x ys = [y | y <- ys, sonAnagramas x y]\n\n-- 5\u00aa soluci\u00f3n\n-- ===========\n\nanagramas5 :: String -> [String] -> [String]\nanagramas5 x = filter (`sonAnagramas` x)\n\n-- 6\u00aa soluci\u00f3n\n-- ===========\n\nanagramas6 :: String -> [String] -> [String]\nanagramas6 x = filter (((==) `on` (sort . map toLower)) x)\n\n-- 7\u00aa soluci\u00f3n\n-- ===========\n\nanagramas7 :: String -> [String] -> [String]\nanagramas7 _ [] = []\nanagramas7 x (y:ys)\n | sonAnagramas7 x y = y : anagramas7 x ys\n | otherwise = anagramas7 x ys\n\nsonAnagramas7 :: String -> String -> Bool\nsonAnagramas7 xs ys = aux (map toLower xs) (map toLower ys)\n where\n aux [] [] = True\n aux [] _ = False\n aux (u:us) vs | u `notElem` vs = False\n | otherwise = aux us (delete u vs)\n\n-- Comparaci\u00f3n de eficiencia\n-- =========================\n\n-- La comparaci\u00f3n es\n-- \u03bb> ej = take (10^6) (permutations \"1234567890\")\n-- \u03bb> length (anagramas \"1234567890\" ej)\n-- 1000000\n-- (2.27 secs, 5,627,236,104 bytes)\n-- \u03bb> length (anagramas2 \"1234567890\" ej)\n-- 1000000\n-- (2.80 secs, 5,513,260,584 bytes)\n-- \u03bb> length (anagramas3 \"1234567890\" ej)\n-- 1000000\n-- (1.86 secs, 5,097,260,856 bytes)\n-- \u03bb> length (anagramas4 \"1234567890\" ej)\n-- 1000000\n-- (2.25 secs, 5,073,260,632 bytes)\n-- \u03bb> length (anagramas5 \"1234567890\" ej)\n-- 1000000\n-- (2.14 secs, 5,009,260,616 bytes)\n-- \u03bb> length (anagramas6 \"1234567890\" ej)\n-- 1000000\n-- (1.58 secs, 4,977,260,976 bytes)\n-- \u03bb> length (anagramas7 \"1234567890\" ej)\n-- 1000000\n-- (6.63 secs, 6,904,821,648 bytes)\n<\/pre>\n