Day2 Part 1

day2_part1.hs

data LetterGroup = TwoChar
                 | ThreeChar
                 deriving (Show, Eq, Ord)

-- PROBLEM 1
-- Call This
calcCheckSum :: [ID] -> Int
calcCheckSum = foldl (*) 1 . map length . groupSort . concat . map (nub . repeats)

twoOrThree :: [LetterGroup] -> [Char] -> [LetterGroup]
twoOrThree acc [_, _] = TwoChar : acc
twoOrThree acc [_, _, _] = ThreeChar : acc
twoOrThree acc _ = acc

repeats :: ID -> [LetterGroup]
repeats = foldl' twoOrThree [] . groupSort

groupSort :: Ord a => [a] -> [[a]]
groupSort = group . sort