Primer elemento repetido

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1. Haskell

   primerRepetido :: Eq a => [a] -> Maybe a primerRepetido [] = Nothing primerRepetido (x:xs) | x `elem` xs = Just x | otherwise = primerRepetido xs

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   primerRepetido :: Eq a => [a] -> Maybe a primerRepetido [] = Nothing primerRepetido (x:xs)   | x `elem` xs = Just x   | otherwise   = primerRepetido xs

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2. Haskell

   primerRepetido :: Eq a => [a] -> Maybe a primerRepetido = go [] where go rs [] = Nothing go rs (x:xs) | elem x rs = Just x | otherwise = go (x:rs) xs

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   primerRepetido :: Eq a => [a] -> Maybe a primerRepetido = go []   where go rs [] = Nothing         go rs (x:xs)           | elem x rs = Just x           | otherwise = go (x:rs) xs

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3. Haskell

   import Data.List (intersect) primerRepetido :: Eq a => [a] -> Maybe a primerRepetido xs | seRepiteUno xs == True = Just (head (repetidos xs)) | seRepiteUno xs == False = Nothing seRepiteUno :: Eq a => [a] -> Bool seRepiteUno (x:[]) = False seRepiteUno (x:xs) | intersect [x] xs == [] = seRepiteUno xs | intersect [x] xs == [x] = True repetidos :: Eq a => [a] -> [a] repetidos (x:[]) = [] repetidos (x:xs) | intersect [x] xs /= [] = [x] ++ repetidos xs | intersect [x] xs == [] = repetidos xs

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   import Data.List (intersect)   primerRepetido :: Eq a => [a] -> Maybe a primerRepetido xs   | seRepiteUno xs == True  = Just (head (repetidos xs))   | seRepiteUno xs == False = Nothing   seRepiteUno :: Eq a => [a] -> Bool seRepiteUno (x:[]) = False seRepiteUno (x:xs)   | intersect [x] xs == [] = seRepiteUno xs   | intersect [x] xs == [x] = True   repetidos :: Eq a => [a] -> [a] repetidos (x:[]) = [] repetidos (x:xs)   | intersect [x] xs /= [] = [x] ++ repetidos xs   | intersect [x] xs == [] = repetidos xs

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4. Haskell

   import Data.List (find, delete) primerRepetido :: Eq a => [a] -> Maybe a primerRepetido xs = find esRepetido xs where esRepetido n = aux n xs where aux n xs = n `elem` (delete n xs)

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   import Data.List (find, delete)   primerRepetido :: Eq a => [a] -> Maybe a primerRepetido xs = find esRepetido xs   where esRepetido n = aux n xs            where aux n xs = n `elem` (delete n xs)

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5. Haskell

   primerRepetido :: Eq a => [a] -> Maybe a primerRepetido xs | null ys = Nothing | otherwise = Just (head ys) where ys = [x | x <- xs, repeticiones x xs >= 2] repeticiones :: Eq a => a -> [a] -> Integer repeticiones _ [] = 0 repeticiones _ [_] = 0 repeticiones x (y:xs) | x == y = 1 + repeticiones x xs | x /= y = repeticiones x xs

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   primerRepetido :: Eq a => [a] -> Maybe a primerRepetido xs   | null ys   = Nothing   | otherwise = Just (head ys)   where ys = [x | x <- xs, repeticiones x xs >= 2]   repeticiones :: Eq a => a -> [a] -> Integer repeticiones _ []  = 0 repeticiones _ [_] = 0 repeticiones x (y:xs)   | x == y = 1 + repeticiones x xs   | x /= y = repeticiones x xs

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