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