Definir la funci\u00f3n<\/p>\n
\n interseccionParcial :: Ord a => Int -> [[a]] -> [a]\n<\/pre>\ntal que (interseccionParcial n xss)<\/code> es la lista de los elementos que pertenecen al menos a n<\/code> conjuntos de xss<\/code>. Por ejemplo,<\/p>\n\n interseccionParcial 1 [[3,4],[4,5,9],[5,4,7]] == [3,4,5,9,7]\n interseccionParcial 2 [[3,4],[4,5,9],[5,4,7]] == [4,5]\n interseccionParcial 3 [[3,4],[4,5,9],[5,4,7]] == [4]\n interseccionParcial 4 [[3,4],[4,5,9],[5,4,7]] == []\n<\/pre>\nSoluciones<\/h4>\n\nimport Data.List (foldl', nub, union, sort)\nimport Test.QuickCheck\n\n-- 1\u00aa soluci\u00f3n\n-- ===========\n\ninterseccionParcial1 :: Ord a => Int -> [[a]] -> [a]\ninterseccionParcial1 n xss = \n [x | x <- sort (elementos xss)\n , pertenecenAlMenos n xss x]\n\nelementos :: Ord a => [[a]] -> [a]\nelementos [] = []\nelementos (xs:xss) = xs `union` elementos xss\n\npertenecenAlMenos :: Ord a => Int -> [[a]] -> a -> Bool\npertenecenAlMenos n xss x =\n length [xs | xs <- xss, x `elem` xs] >= n\n \n-- 2\u00aa soluci\u00f3n\n-- ===========\n\ninterseccionParcial2 :: Ord a => Int -> [[a]] -> [a]\ninterseccionParcial2 n xss = \n [x | x <- sort (elementos2 xss)\n , pertenecenAlMenos2 n xss x]\n\nelementos2 :: Ord a => [[a]] -> [a]\nelementos2 = foldl' union []\n \npertenecenAlMenos2 :: Ord a => Int -> [[a]] -> a -> Bool\npertenecenAlMenos2 n xss x =\n length (filter (x `elem`) xss) >= n\n \n-- 3\u00aa soluci\u00f3n\n-- ===========\n\ninterseccionParcial3 :: Ord a => Int -> [[a]] -> [a]\ninterseccionParcial3 n xss = \n [x | x <- sort (nub (concat xss))\n , length [xs | xs <- xss, x `elem` xs] >= n]\n\n-- Comprobaci\u00f3n de equivalencia\n-- ============================\n\n-- La propiedad es\nprop_interseccionParcial :: Positive Int -> [[Int]] -> Bool\nprop_interseccionParcial (Positive n) xss =\n all (== interseccionParcial1 n yss)\n [interseccionParcial2 n yss,\n interseccionParcial3 n yss]\n where yss = map nub xss\n\n-- La comprobaci\u00f3n es\n-- \u03bb> quickCheck prop_interseccionParcial\n-- +++ OK, passed 100 tests.\n<\/pre>\n