El problema de la bandera tricolor consiste en lo siguiente: Dada un lista de objetos xs que pueden ser rojos, amarillos o morados, se pide devolver una lista ys que contiene los elementos de xs, primero los rojos, luego los amarillos y por \u00faltimo los morados.<\/p>\n
Definir el tipo de dato Color para representar los colores con los constructores R, A y M correspondientes al rojo, azul y morado y la funci\u00f3n<\/p>\n
\n banderaTricolor :: [Color] -> [Color]\n<\/pre>\ntal que (banderaTricolor xs) es la bandera tricolor formada con los elementos de xs. Por ejemplo,<\/p>\n
\n bandera [M,R,A,A,R,R,A,M,M] == [R,R,R,A,A,A,M,M,M]\n bandera [M,R,A,R,R,A] == [R,R,R,A,A,M]\n<\/pre>\nSoluciones<\/h4>\n\nimport Data.List (sort)\nimport Test.QuickCheck (Arbitrary(arbitrary), elements, quickCheck)\n\ndata Color = R | A | M\n deriving (Show, Eq, Ord, Enum)\n\n-- 1\u00aa soluci\u00f3n\n-- ===========\n\nbanderaTricolor1 :: [Color] -> [Color]\nbanderaTricolor1 xs =\n [x | x <- xs, x == R] ++\n [x | x <- xs, x == A] ++\n [x | x <- xs, x == M]\n\n-- 2\u00aa soluci\u00f3n\n-- ===========\n\nbanderaTricolor2 :: [Color] -> [Color]\nbanderaTricolor2 xs =\n colores R ++ colores A ++ colores M\n where colores c = filter (== c) xs\n\n-- 3\u00aa soluci\u00f3n\n-- ===========\n\nbanderaTricolor3 :: [Color] -> [Color]\nbanderaTricolor3 xs =\n concat [[x | x <- xs, x == c] | c <- [R,A,M]]\n\n-- 4\u00aa soluci\u00f3n\n-- ===========\n\nbanderaTricolor4 :: [Color] -> [Color]\nbanderaTricolor4 xs = aux xs ([],[],[])\n where aux [] (rs,as,ms) = rs ++ as ++ ms\n aux (R:ys) (rs,as,ms) = aux ys (R:rs, as, ms)\n aux (A:ys) (rs,as,ms) = aux ys ( rs, A:as, ms)\n aux (M:ys) (rs,as,ms) = aux ys ( rs, as, M:ms)\n\n-- 5\u00aa soluci\u00f3n\n-- ===========\n\nbanderaTricolor5 :: [Color] -> [Color]\nbanderaTricolor5 = sort\n\n-- Comprobaci\u00f3n de equivalencia\n-- ============================\n\ninstance Arbitrary Color where\n arbitrary = elements [A,R,M]\n\n-- La propiedad es\nprop_banderaTricolor :: [Color] -> Bool\nprop_banderaTricolor xs =\n all (== banderaTricolor1 xs)\n [banderaTricolor2 xs,\n banderaTricolor3 xs,\n banderaTricolor4 xs,\n banderaTricolor5 xs]\n\nverifica_banderaTricolor :: IO ()\nverifica_banderaTricolor =\n quickCheck prop_banderaTricolor\n\n-- La comprobaci\u00f3n es\n-- \u03bb> verifica_banderaTricolor\n-- +++ OK, passed 100 tests.\n\n-- Comparaci\u00f3n de eficiencia\n-- =========================\n\n-- La comparaci\u00f3n es\n-- \u03bb> bandera n = concat [replicate n c | c <- [M,R,A]]\n-- \u03bb> length (banderaTricolor1 (bandera (10^6)))\n-- 3000000\n-- (1.51 secs, 1,024,454,768 bytes)\n-- \u03bb> length (banderaTricolor1 (bandera (2*10^6)))\n-- 6000000\n-- (2.94 secs, 2,048,454,832 bytes)\n-- \u03bb> length (banderaTricolor2 (bandera (2*10^6)))\n-- 6000000\n-- (2.35 secs, 1,232,454,920 bytes)\n-- \u03bb> length (banderaTricolor3 (bandera (2*10^6)))\n-- 6000000\n-- (4.28 secs, 2,304,455,360 bytes)\n-- \u03bb> length (banderaTricolor4 (bandera (2*10^6)))\n-- 6000000\n-- (3.01 secs, 1,904,454,672 bytes)\n-- \u03bb> length (banderaTricolor5 (bandera (2*10^6)))\n-- 6000000\n-- (2.47 secs, 1,248,454,744 bytes)\n<\/pre>\n