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re: Daily Coding Problem #1 VIEW POST

FULL DISCUSSION
 

I have come up with this

sumPair :: Num a => (a, a) -> a
sumPair (x, y) = x + y

isMoreThanOnce :: Eq a => a -> [a] -> Bool
isMoreThanOnce x xs = (>1).length.(filter (==x)) $ xs

createPairs :: (Num a, Eq a) => [a] -> a -> [(a, a)]
createPairs xs x
  | isMoreThanOnce x xs = tuples.addX.whithoutX $ xs
  | otherwise = tuples.whithoutX $ xs
  where whithoutX = filter (/=x)
        tuples = map ((,) x)
        addX = (x:)

createAllPairs :: (Num a, Eq a) => [a] -> [(a, a)]
createAllPairs xs = flatmap (createPairs xs) xs

problem :: (Num a, Eq a) => a -> [a] -> Bool
problem k xs = elem k.map sumPair.createAllPairs $ xs
 

Here's another solution in Haskell

import qualified Data.Set as Set

solve :: Integral a => a -> [a] -> Bool
solve = solve' Set.empty

solve' :: Integral a => Set.Set a -> a -> [a] -> Bool
solve' _ _ [] = False
solve' possibleAddends targetSum (x:xs)
  | Set.member x possibleAddends = True
  | otherwise = solve' (Set.insert addend possibleAddends) targetSum xs
  where addend = targetSum - x
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