Suma de elementos en posiciones dadas

6 Comentarios

1. Haskell

   sumaEnPosicion :: [Int] -> [Int] -> Int sumaEnPosicion xs ys = sum [x | x <- xs, y <- ys, y < length xs, xs !! y == x]

   1 2	sumaEnPosicion :: [Int] -> [Int] -> Int sumaEnPosicion xs ys = sum [x | x <- xs, y <- ys, y < length xs, xs !! y == x]

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   1. Esta solución se puede mejorar eliminando el primer generador x<-xs, tal y como propone, por ejemplo, Chema Cortés en su definición.

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2. Haskell

   sumaEnPosicion _ [] = 0 sumaEnPosicion xs (p:ys) | p < length xs = xs !! p + s | otherwise = s where s = sumaEnPosicion xs ys

   1 2 3 4

   sumaEnPosicion _ [] = 0 sumaEnPosicion xs (p:ys) | p < length xs = xs !! p + s                          | otherwise = s     where s = sumaEnPosicion xs ys

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3. Haskell

   sumaEnPosicion :: [Int] -> [Int] -> Int sumaEnPosicion xs ys = foldr1 (+) [pos xs y | y <- ys] where pos :: [Int] -> Int -> Int pos xs y | length xs < y + 1 = 0 | otherwise = xs !! y

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   sumaEnPosicion :: [Int] -> [Int] -> Int sumaEnPosicion xs ys = foldr1 (+) [pos xs y | y <- ys]   where pos :: [Int] -> Int -> Int         pos xs y | length xs < y + 1 = 0                  | otherwise         = xs !! y

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4. O(n * max({m}))

   Haskell

   sumaEnPosicion xs = sum.map ((xs ++ repeat 0)!!)

   1	sumaEnPosicion xs = sum.map ((xs ++ repeat 0)!!)

   O(n * m)

   Haskell

   import Prelude hiding ((!!)) import Data.List.Safe sumaEnPosicion xs = sum.mapMaybe (xs!!)

   1 2 3 4

   import Prelude hiding ((!!)) import Data.List.Safe   sumaEnPosicion xs = sum.mapMaybe (xs!!)

   O((n + m) log n)

   Haskell

   import qualified Data.Map as M sumaEnPosicion xs = let m = M.fromList (zip [0..] xs) in sum.mapMaybe (flip M.lookup m)

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   import qualified Data.Map as M   sumaEnPosicion xs =     let m = M.fromList (zip [0..] xs)     in  sum.mapMaybe (flip M.lookup m)

   O((n + m) log m)

   Haskell

   sumaEnPosicion xs ys = let s = S.fromList ys in sum [x | (i, x) <- zip [0..] xs, S.member i s]

   1 2 3

   sumaEnPosicion xs ys =     let s = S.fromList ys     in  sum [x | (i, x) <- zip [0..] xs, S.member i s]

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5. Haskell

   sumaEnPosicion :: [Int] -> [Int] -> Int sumaEnPosicion xs ys = sum [ x | (x,n) <- zip xs [0..], n `elem` ys ]

   1 2	sumaEnPosicion :: [Int] -> [Int] -> Int sumaEnPosicion xs ys = sum [ x | (x,n) <- zip xs [0..], n `elem` ys ]

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