Selección hasta el primero que falla inclusive

PorJosé A. Alonso 18-junio-201429-noviembre-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]

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-- 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

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-- 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.

7 Comentarios

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)

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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)

seleccionConFallo :: (a -> Bool) -> [a] -> [a]
seleccionConFallo p (x:xs) | p x = x : seleccionConFallo p xs
                             | otherwise = [x]
seleccionConFallo _ _ = []

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seleccionConFallo :: (a -> Bool) -> [a] -> [a]

seleccionConFallo p (x:xs) | p x = x : seleccionConFallo p xs

| otherwise = [x]

seleccionConFallo _ _ = []

seleccionConFallo p [] = []
seleccionConFallo p (x:xs) 
    | verificaP p x = x: seleccionConFallo p xs
    | otherwise     = [x]

verificaP p x | p x       = True
              | otherwise = False

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seleccionConFallo p [] = []

seleccionConFallo p (x:xs)

| verificaP p x = x: seleccionConFallo p xs

| otherwise = [x]

verificaP p x | p x = True

| otherwise = False

Daniel Sánchez dice:

18-junio-2014 a las 09:42

Haskell

seleccionConFallo p [] = [] seleccionConFallo p (x:xs)| p x = x: seleccionConFallo p xs | otherwise = [x]

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seleccionConFallo p [] = []
seleccionConFallo p (x:xs)| p x = x: seleccionConFallo p xs
| otherwise = [x]

Responder
Loles Valverde dice:

18-junio-2014 a las 09:44

Haskell

seleccionConFallo :: (a -> Bool) -> [a] -> [a] seleccionConFallo p xs = take l xs where l = (length (takeWhile p xs))+1

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seleccionConFallo :: (a -> Bool) -> [a] -> [a]
seleccionConFallo p xs = take l xs
where l = (length (takeWhile p xs))+1

Responder

seleccionConFallo :: (a -> Bool) -> [a] -> [a]
seleccionConFallo p [] = []
seleccionConFallo p (x:xs) | p x       = x :seleccionConFallo p xs
                           | otherwise = [x]

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seleccionConFallo :: (a -> Bool) -> [a] -> [a]

seleccionConFallo p [] = []

seleccionConFallo p (x:xs) | p x = x :seleccionConFallo p xs

| otherwise = [x]

aguruipoy dice:

19-junio-2014 a las 07:32

Haskell

seleccionConFallo :: (a -> Bool) -> [a] -> [a] seleccionConFallo p xs = if all p xs then xs else (fst (span p xs)) ++ [head (snd (span p xs))]

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seleccionConFallo :: (a -> Bool) -> [a] -> [a]
seleccionConFallo p xs =
if all p xs then xs
else (fst (span p xs)) ++ [head (snd (span p xs))]

Responder

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