http://qiita.com/items/cbc3af152ee3f50a822f の問題をhaskellで解いてみた

poker.hs

import Data.List
import Test.HUnit

poker :: String -> String
poker = check . split

split :: String -> [(String, String)]
split ('D':'1':'0':xs) = [("D", "10")] ++ split xs
split ('C':'1':'0':xs) = [("C", "10")] ++ split xs
split ('S':'1':'0':xs) = [("S", "10")] ++ split xs
split ('H':'1':'0':xs) = [("H", "10")] ++ split xs
split ('D':numberString:xs) = ("D", [numberString]) : split xs
split ('C':numberString:xs) = ("C", [numberString]) : split xs
split ('S':numberString:xs) = ("S", [numberString]) : split xs
split ('H':numberString:xs) = ("H", [numberString]) : split xs
split [] = []

countSameRank :: [String] -> String -> Int
countSameRank [] x = 0
countSameRank (y:ys) x
  | x == y = 1 + (countSameRank ys x)
  | otherwise = countSameRank ys x
                       

check :: [(String, String)] -> String
check cards 
  | maxCount == 4 = "4K"
  | maxCount == 3 = if rankCounts !! 1 == 2
                    then "FH"
                    else "3K"
  | maxCount == 2 = if rankCounts !! 1 == 2
                    then "2P"
                    else "1P"
  | otherwise = "--"
  where
    ranks = map snd cards
    seeds = nub ranks
    rankCounts = reverse . sort $ map (countSameRank ranks) seeds
    maxCount = maximum rankCounts

tests = test ["FH" ~=? poker "D3C3C10D10S3"]