Operación sobre todos los pares
Definir la función
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todosPares :: (a -> b -> c) -> [a] -> [b] -> [c] |
tal que (todosPares f xs ys) es el resultado de aplicar la operación f a todos los pares de xs e ys. Por ejemplo,
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todosPares (*) [2,3,5] [7,11] == [14,22,21,33,35,55] todosPares (\x y -> x:show y) "ab" [7,5] == ["a7","a5","b7","b5"] |
Soluciones
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-- 1ª definición (por comprensión) todosPares1 :: (a -> b -> c) -> [a] -> [b] -> [c] todosPares1 f xs ys = [f x y | x <- xs, y <- ys] -- 2ª definición (por recursión) todosPares2 :: (a -> b -> c) -> [a] -> [b] -> [c] todosPares2 _ [] _ = [] todosPares2 f (x:xs) ys = map (f x) ys ++ todosPares2 f xs ys -- 3ª definición (recursión con auxiliar) todosPares3 :: (a -> b -> c) -> [a] -> [b] -> [c] todosPares3 f xs ys = aux xs where aux [] = [] aux (x:xs) = map (f x) ys ++ aux xs -- 4ª definición (recursión con auxiliar) todosPares4 :: (a -> b -> c) -> [a] -> [b] -> [c] todosPares4 f xs ys = (foldr (\x zs -> map (f x) ys ++ zs) []) xs |