第17回オフラインリアルタイムどう書くの参考問題をHaskellで書いた

実行効率は考慮せず素朴な方法で書きました。

base.hs

import Control.Applicative

--基数変換
convertBase :: Int -> Int -> [Int]
convertBase n b = convertBase' n b []
    where
        convertBase' :: Int -> Int -> [Int] -> [Int]
        convertBase' 0 _ ns = ns
        convertBase' n b ns = let q = n `div` b
                                  r = n `mod` b
                              in convertBase' q b (r:ns)
--回文かチェック
isPalindrome :: [Int] -> Bool
isPalindrome ns = ns == reverse ns

solve :: Int -> String
solve n = let base = concatMap (\b -> if isPalindrome $ convertBase n b then [b] else []) [2..n]
          in if null base
            then "-"
            else listToString base
    where
        listToString (n:[]) = show n 
        listToString (n:ns) = show n ++ "," ++ listToString ns

main = do
    tests <- lines <$> readFile "test.txt"
    mapM (\t -> print $ runTest solve t) tests
    where
        runTest :: (Int -> String) -> String -> Bool
        runTest f t = let [input, output] = words t
                      in f (read input :: Int) == output 

test.hs

17301   5,38,100,218,236,5766,17300
2   -
1   -
3   2
4   3
5   2,4
6   5
10  3,4,9
101 10,100
1001    10,25,76,90,142,1000
10001   10,24,30,42,80,100,136,10000
1212    22,100,201,302,403,605,1211
123412  62,100,205,215,30852,61705,123411
5179    5178
4919    4918
5791    5790
5498    2748,5497
453 150,452
134 66,133
8489    27,652,8488
1234    22,616,1233
5497    41,238,5496
4763    19,35,432,4762
3974    17,27,1986,3973
3521    44,55,502,3520
5513    20,38,53,148,5512
8042    23,29,60,4020,8041
7442    37,60,121,3720,7441
4857    25,1618,4856
22843   49,69,91,141,430,22842
194823  84,121,21646,64940,194822
435697  160,169,235,626,1822,435696
142 3,7,70,141
886 5,14,442,885
3102    7,65,93,140,281,516,1033,1550,3101
17326   11,28,99,105,8662,17325
32982   13,72,238,477,716,1433,5496,10993,16490,32981
36  5,8,11,17,35
37  6,36
251 8,250
252 5,10,17,20,27,35,41,62,83,125,251
253 12,14,22,252
6643    2,3,9,81,90,510,948,6642
5040    71,79,83,89,104,111,119,125,139,143,167,179,209,239,251,279,314,335,359,419,503,559,629,719,839,1007,1259,1679,2519,5039
9240    23,38,62,104,109,119,131,139,153,164,167,209,219,230,263,279,307,329,384,419,439,461,615,659,769,839,923,1154,1319,1539,1847,2309,3079,4619,9239