ぶどうの房パズル

Grape.hs

import Control.Monad
import Data.List

main :: IO ()
main = interact $ format . solve . read

format :: [[Int]] -> String
format = unlines . map (unwords . map show)

solve :: Int -> [[Int]]
solve = head . filter valid . candidates

valid :: [[Int]] -> Bool
valid xs = nub ys == ys where ys = concat xs

candidates :: Int -> [[[Int]]]
candidates n = map (take n . iterate diff) $ replicateM n [1 .. sum [1..n]]

diff :: [Int] -> [Int]
diff xs = map abs $ zipWith (-) xs $ tail xs