Permutación de elementos consecutivos
Definir la función
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permutaConsecutivos :: [a] -> [a] |
tal que (permutaConsecutivos xs) es la lista obtenida permutando los elementos consecutivos de xs. Por ejemplo,
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permutaConsecutivos [1..8] == [2,1,4,3,6,5,8,7] permutaConsecutivos [1..9] == [2,1,4,3,6,5,8,7,9] permutaConsecutivos "simplemente" == "ispmelemtne" |
Soluciones
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import Data.Array -- 1ª solución -- =========== permutaConsecutivos :: [a] -> [a] permutaConsecutivos (x:y:zs) = y : x : permutaConsecutivos zs permutaConsecutivos xs = xs -- 2ª solución -- =========== permutaConsecutivos2 :: [a] -> [a] permutaConsecutivos2 xs | even n = elems (array (1,n) [(i,f i) | i <- [1..n]]) | otherwise = elems (array (1,n) ((n,v!n) : [(i,f i) | i <- [1..n-1]])) where n = length xs v = listArray (1,n) xs f i | even i = v ! (i - 1) | otherwise = v ! (i + 1) -- Comparación de eficiencia -- ========================= -- La comparación es -- λ> length (permutaConsecutivos [1..(3*10^6)]) -- 3000000 -- (2.21 secs, 504,102,648 bytes) -- λ> length (permutaConsecutivos2 [1..(3*10^6)]) -- 3000000 -- (6.18 secs, 1,248,127,688 bytes) |
Pensamiento
Entre el vivir y el soñar
hay una tercera cosa.
Adivínala.Antonio Machado