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module Main (main) where
import Control.Monad (when)
import Data.List (foldl')
import Data.Maybe (fromJust, isNothing)
import System.Exit (die)
exampleExpectedOutput = 62
parseInput :: String -> IO [Int]
parseInput filename = do
input <- readFile filename
return $ map read $ lines input
validate :: [Int] -> Int -> Bool
validate list n = processInput list
where
processInput :: [Int] -> Bool
processInput (_:[]) = False
processInput (x:xs) = (foldl' (\acc i -> acc || (x + i == n && x /= i)) False xs) || processInput xs
isContiguousSum :: Int -> [Int] -> Int -> Maybe Int
isContiguousSum target list counter
| sum' == target = Just $ (minimum lst) + (maximum lst)
| sum' < target = isContiguousSum target list (counter + 1)
| otherwise = Nothing
where
lst = take counter list
sum' = sum lst
compute :: Int -> [Int] -> Int
compute len list
| validate (take len list) (list !! len) = compute len $ tail list
| otherwise = list !! len
compute' :: Int -> [Int] -> Int
compute' target list = case isContiguousSum target list 2 of
Nothing -> compute' target (tail list)
Just a -> a
main :: IO ()
main = do
example <- parseInput "example"
let exampleOutput = compute 5 example
exampleOutput' = compute' exampleOutput example
when (exampleOutput' /= exampleExpectedOutput) (die $ "example failed: got " ++ show exampleOutput' ++ " instead of " ++ show exampleExpectedOutput)
input <- parseInput "input"
print $ compute' (compute 25 input) input
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