Sumas de posiciones pares e impares

PorJosé A. Alonso 1-diciembre-20168-diciembre-2016

Definir la función

   sumasParesImpares :: [Integer] -> (Integer,Integer)

1	sumasParesImpares :: [Integer] -> (Integer,Integer)

tal que (sumasParesImpares) xs es el par formado por la suma de los elementos de xs en posiciones pares y por la suma de los elementos de xs en posiciones impares. Por ejemplo,

   sumasParesImpares []         ==  (0,0)
   sumasParesImpares [3]        ==  (3,0)
   sumasParesImpares [3,2]      ==  (3,2)
   sumasParesImpares [3,2,1]    ==  (4,2)
   sumasParesImpares [3,2,1,5]  ==  (4,7)
   sumasParesImpares [1..10^7]  ==  (25000000000000,25000005000000)

sumasParesImpares [] == (0,0)

sumasParesImpares [3] == (3,0)

sumasParesImpares [3,2] == (3,2)

sumasParesImpares [3,2,1] == (4,2)

sumasParesImpares [3,2,1,5] == (4,7)

sumasParesImpares [1..10^7] == (25000000000000,25000005000000)

Soluciones

-- 1ª solución
sumasParesImpares1 :: [Integer] -> (Integer,Integer)
sumasParesImpares1 xs =
  (sum [x | (x,n) <- xns, even n],
   sum [x | (x,n) <- xns, odd n])
  where xns = zip xs [0..]

-- 2ª solución
sumasParesImpares2 :: [Integer] -> (Integer,Integer)
sumasParesImpares2 xs = aux xs (0,0)
  where aux (x1:x2:xs) (a,b) = aux xs (x1+a,x2+b)
        aux [x]        (a,b) = (x+a,b)
        aux []         (a,b) = (a,b)
  
-- Comparación de eficiencia
--    λ> sumasParesImpares1 [1..10^6]
--    (250000000000,250000500000)
--    (4.48 secs, 731,994,904 bytes)
--    λ> sumasParesImpares2 [1..10^6]
--    (250000000000,250000500000)
--    (1.78 secs, 235,663,400 bytes)

-- 1ª solución

sumasParesImpares1 :: [Integer] -> (Integer,Integer)

sumasParesImpares1 xs =

(sum [x | (x,n) <- xns, even n],

sum [x | (x,n) <- xns, odd n])

where xns = zip xs [0..]

-- 2ª solución

sumasParesImpares2 :: [Integer] -> (Integer,Integer)

sumasParesImpares2 xs = aux xs (0,0)

where aux (x1:x2:xs) (a,b) = aux xs (x1+a,x2+b)

aux [x] (a,b) = (x+a,b)

aux [] (a,b) = (a,b)

-- Comparación de eficiencia

-- λ> sumasParesImpares1 [1..10^6]

-- (250000000000,250000500000)

-- (4.48 secs, 731,994,904 bytes)

-- λ> sumasParesImpares2 [1..10^6]

-- (250000000000,250000500000)

-- (1.78 secs, 235,663,400 bytes)

9 Comentarios

sumasParesImpares :: [Integer] -> (Integer,Integer)
sumasParesImpares ns = auxI ns (0,0)
  where
    auxI []     (a,b) = (a,b)
    auxI (n:ns) (a,b) = auxP ns (a+n,b)
    auxP []     (a,b) = (a,b)
    auxP (n:ns) (a,b) = auxI ns (a,b+n)

sumasParesImpares :: [Integer] -> (Integer,Integer)

sumasParesImpares ns = auxI ns (0,0)

where

auxI [] (a,b) = (a,b)

auxI (n:ns) (a,b) = auxP ns (a+n,b)

auxP [] (a,b) = (a,b)

auxP (n:ns) (a,b) = auxI ns (a,b+n)

Responder

sumasParesImpares :: [Integer] -> (Integer, Integer)
sumasParesImpares []       = (0,0)
sumasParesImpares [x]      = (x,0)
sumasParesImpares (x:y:xs) = (x + si, y + sp)
  where (si,sp) = sumasParesImpares xs

sumasParesImpares :: [Integer] -> (Integer, Integer)

sumasParesImpares [] = (0,0)

sumasParesImpares [x] = (x,0)

sumasParesImpares (x:y:xs) = (x + si, y + sp)

where (si,sp) = sumasParesImpares xs

Responder

sumasParesImpares :: [Integer] -> (Integer,Integer)
sumasParesImpares [] = (0,0)
sumasParesImpares [x] = (x,0)
sumasParesImpares (x:y:xs) = suma (x,y) (sumasParesImpares xs)
  where suma (a,b) (x,y) = (a+x,b+y)

sumasParesImpares :: [Integer] -> (Integer,Integer)

sumasParesImpares [] = (0,0)

sumasParesImpares [x] = (x,0)

sumasParesImpares (x:y:xs) = suma (x,y) (sumasParesImpares xs)

where suma (a,b) (x,y) = (a+x,b+y)

Responder

josejuan dice:

1-diciembre-2016 a las 18:22

Haskell

import Control.Arrow (first, second) sumasParesImpares = foldr id (0,0) . zipWith (.(+)) (cycle [first, second])

1
2
3

import Control.Arrow (first, second)

sumasParesImpares = foldr id (0,0) . zipWith (.(+)) (cycle [first, second])

Responder

{-# LANGUAGE TupleSections #-}
instance (Num a, Num b) => Num (a, b) where
  (a, b) + (c, d) = (a + c, b + d)
  fromInteger x = (fromInteger x, fromInteger x)

sumasParesImpares = sum . zipWith id (cycle [(,0),(0,)])

{-# LANGUAGE TupleSections #-}

instance (Num a, Num b) => Num (a, b) where

(a, b) + (c, d) = (a + c, b + d)

fromInteger x = (fromInteger x, fromInteger x)

sumasParesImpares = sum . zipWith id (cycle [(,0),(0,)])

Responder

Por plegados:

sumasParesImpares :: [Integer] -> (Integer,Integer)
sumasParesImpares =
    invertir . foldr (\ n (a,b,c) -> (a+1 `mod` 2,c,n+b)) (0,0,0)
  where invertir :: (Integer,Integer,Integer) -> (Integer, Integer)
        invertir (0,a,b) = (a,b)
        invertir (_,a,b) = (b,a)

sumasParesImpares :: [Integer] -> (Integer,Integer)

sumasParesImpares =

invertir . foldr (\ n (a,b,c) -> (a+1 `mod` 2,c,n+b)) (0,0,0)

where invertir :: (Integer,Integer,Integer) -> (Integer, Integer)

invertir (0,a,b) = (a,b)

invertir (_,a,b) = (b,a)

Por recursión con contador:

sumasParesImpares2 :: [Integer] -> (Integer,Integer)
sumasParesImpares2 = suma (0,0)
  where suma :: (Integer,Integer) -> [Integer] -> (Integer,Integer)
        suma (x,y) (a:b:ns) = suma (x+a,y+b) ns
        suma (x,y) [a]      = (x+a,y)
        suma (x,y) _        = (x,y)

sumasParesImpares2 :: [Integer] -> (Integer,Integer)

sumasParesImpares2 = suma (0,0)

where suma :: (Integer,Integer) -> [Integer] -> (Integer,Integer)

suma (x,y) (a:b:ns) = suma (x+a,y+b) ns

suma (x,y) [a] = (x+a,y)

suma (x,y) _ = (x,y)

Responder

sumasParesImpares :: [Integer] -> (Integer,Integer)
sumasParesImpares xs = (x , sum xs - x)
  where x = sumaPares 0 xs

sumaPares :: Int -> [Integer] -> Integer
sumaPares _ []     = 0
sumaPares n (x:xs) | n `mod` 2 == 0 = x + sumaPares (n+1) xs
                   | otherwise      = sumaPares (n+1) xs

sumasParesImpares :: [Integer] -> (Integer,Integer)

sumasParesImpares xs = (x , sum xs - x)

where x = sumaPares 0 xs

sumaPares :: Int -> [Integer] -> Integer

sumaPares _ [] = 0

sumaPares n (x:xs) | n `mod` 2 == 0 = x + sumaPares (n+1) xs

| otherwise = sumaPares (n+1) xs

Responder

sumasParesImpares :: [Integer] -> (Integer,Integer)
sumasParesImpares [] = (0,0)
sumasParesImpares [x] = (x,0)
sumasParesImpares xs = (imp xs, par xs)
                  where imp xs = sum [x | (x,c) <- zip xs [1..], odd c]
                        par xs = sum [x | (x,c) <- zip xs [1..], even c]

sumasParesImpares :: [Integer] -> (Integer,Integer)

sumasParesImpares [] = (0,0)

sumasParesImpares [x] = (x,0)

sumasParesImpares xs = (imp xs, par xs)

where imp xs = sum [x | (x,c) <- zip xs [1..], odd c]

par xs = sum [x | (x,c) <- zip xs [1..], even c]

Responder

sumaParesImpares :: [Integer] -> (Integer,Integer)
sumaParesImpares []  = (0,0)
sumaParesImpares [x] = (x,0)
sumaParesImpares xs  = (m,n)
  where m = sum [p | (p,s) <- zip xs [0..], even s]
        n = sum [p | (p,s) <- zip xs [0..], odd s]

sumaParesImpares :: [Integer] -> (Integer,Integer)

sumaParesImpares [] = (0,0)

sumaParesImpares [x] = (x,0)

sumaParesImpares xs = (m,n)

where m = sum [p | (p,s) <- zip xs [0..], even s]

n = sum [p | (p,s) <- zip xs [0..], odd s]

Responder

Sumas de posiciones pares e impares

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