Problem Definition :
When John was a little kid he didn't have much to do. There was no internet, no Facebook, and no programs to hack on. So he did the only thing he could... he evaluated the beauty of strings in a quest to discover the most beautiful string in the world.
Given a string s, little Johnny defined the beauty of the string as the sum of the beauty of the letters in it. The beauty of each letter is an integer between 1 and 26, inclusive, and no two letters have the same beauty. Johnny doesn't care about whether letters are uppercase or lowercase, so that doesn't affect the beauty of a letter. (Uppercase 'F' is exactly as beautiful as lowercase 'f', for example.)
You're a student writing a report on the youth of this famous hacker. You found the string that Johnny considered most beautiful. What is the maximum possible beauty of this string?
Your program should accept as its first argument a path to a filename. Each line in this file has a sentence.
Print out the maximum beauty for the string.
I'm still very new to Haskell, trying to wrap my head around things like monads and such, so some of the constructs might seem overly simplistic. I would like any sort of criticism from efficiency to idiomatic usage of Haskell. I harbor suspicions that my countSort function is inefficient as I would solve this using a dictionary in an imperative language but that sort of mutable solution seemed out of place in my understanding of Haskell and I couldn't decide if lazy evaluation would make up for it. Either way the speed was actually a bit faster than what I've implemented in imperative languages.
I thought about generalizing the beauty function by moving the toUpper/IsAlpha out of the method to change it's signature to something like [a] -> Int, but it felt outside of the point of the problem, and I honestly couldn't think of a use for this function outside of this problem.
import Data.List import Data.Char import Data.Ord import System.Environment countSort :: Ord a => [a] -> [[a]] countSort x = sortBy (flip $ comparing length) (group $ sort x) maximumStringBeauty :: String -> Int maximumStringBeauty x = maximumBeautyInner (countSort . map toUpper $ filter isAlpha x) 26 where maximumBeautyInner  _ = 0 maximumBeautyInner (x : xs) maxVal = (length x) * maxVal + maximumBeautyInner xs (maxVal - 1) main :: IO () main = do args <- getArgs let path = args !! 0 file <- readFile path putStrLn . unlines . map (show . maximumStringBeauty) . lines $ file