Selección hasta el primero que falla inclusive

José A. Alonso, 18-junio-2014

Enunciado

-- Definir la función
--    seleccionConFallo :: (a -> Bool) -> [a] -> [a]
-- tal que (seleccionConFallo p xs) es la lista de los elementos de xs
-- que cumplen el predicado p hasta el primero que no lo cumple
-- inclusive. Por ejemplo,
--    seleccionConFallo (<5) [3,2,5,7,1,0]  ==  [3,2,5]
--    seleccionConFallo odd [1..4]          ==  [1,2]
--    seleccionConFallo odd [1,3,5]         ==  [1,3,5]
--    seleccionConFallo (<5) [10..20]       ==  [10]

Soluciones

-- 1ª solución (por recursión):
seleccionConFallo1 :: (a -> Bool) -> [a] -> [a]
seleccionConFallo1 p []                 = []
seleccionConFallo1 p (x:xs) | p x       = x : seleccionConFallo1 p xs
                            | otherwise = [x]
 
-- 2ª solución (con span):
seleccionConFallo2 :: (a -> Bool) -> [a] -> [a]
seleccionConFallo2 p xs = ys ++ take 1 zs
    where (ys,zs) = span p xs

Referencia

El ejercicio está basado en el problema del 29 de abril de 1HaskellADay.

Medio

Orden superior, Recursión, span, take

7 soluciones de “Selección hasta el primero que falla inclusive”

Responder

Luicanmar

18-junio-2014

seleccionConFallo :: (a -> Bool) -> [a] -> [a]
seleccionConFallo p xs 
    | length (fst (span p xs)) < length xs = (fst (span p xs))++[head (snd(span p xs))]
    | otherwise                            = fst (span p xs)

Responder
luiporpir
18-junio-2014
seleccionConFallo :: (a -> Bool) -> [a] -> [a] seleccionConFallo p (x:xs) | p x = x : seleccionConFallo p xs | otherwise = [x] seleccionConFallo _ _ = []
seleccionConFallo :: (a -> Bool) -> [a] -> [a] seleccionConFallo p (x:xs) | p x = x : seleccionConFallo p xs | otherwise = [x] seleccionConFallo _ _ = []
Responder
Daniel Simon Aldana
18-junio-2014
seleccionConFallo p [] = [] seleccionConFallo p (x:xs) | verificaP p x = x: seleccionConFallo p xs | otherwise = [x] verificaP p x | p x = True | otherwise = False
seleccionConFallo p [] = [] seleccionConFallo p (x:xs) | verificaP p x = x: seleccionConFallo p xs | otherwise = [x] verificaP p x | p x = True | otherwise = False
Responder
Daniel Sánchez
18-junio-2014
seleccionConFallo p [] = [] seleccionConFallo p (x:xs)| p x = x: seleccionConFallo p xs | otherwise = [x]
seleccionConFallo p [] = [] seleccionConFallo p (x:xs)| p x = x: seleccionConFallo p xs | otherwise = [x]
Responder
Loles Valverde
18-junio-2014
seleccionConFallo :: (a -> Bool) -> [a] -> [a] seleccionConFallo p xs = take l xs where l = (length (takeWhile p xs))+1
seleccionConFallo :: (a -> Bool) -> [a] -> [a] seleccionConFallo p xs = take l xs where l = (length (takeWhile p xs))+1
Responder
Vicsotron
18-junio-2014
seleccionConFallo :: (a -> Bool) -> [a] -> [a] seleccionConFallo p [] = [] seleccionConFallo p (x:xs) | p x = x :seleccionConFallo p xs | otherwise = [x]
seleccionConFallo :: (a -> Bool) -> [a] -> [a] seleccionConFallo p [] = [] seleccionConFallo p (x:xs) | p x = x :seleccionConFallo p xs | otherwise = [x]
Responder
aguruipoy
19-junio-2014
seleccionConFallo :: (a -> Bool) -> [a] -> [a] seleccionConFallo p xs = if all p xs then xs else (fst (span p xs)) ++ [head (snd (span p xs))]
seleccionConFallo :: (a -> Bool) -> [a] -> [a] seleccionConFallo p xs = if all p xs then xs else (fst (span p xs)) ++ [head (snd (span p xs))]