魔方陣を作ってみる
30分プログラム、その784。魔方陣を作ってみた。
最初はリストモナドでベタ書きしようかと思ったけど
magicSquare = do a <- [1..9] b <- delete a [1..9] c <- delete b $ delete a [1..9] .... guard ... return ...
みたいなひどいことになりそうだったのでやめました、まる。
使い方
*Main> magicSquare [[[2,7,6],[9,5,1],[4,3,8]],[[2,9,4],[7,5,3],[6,1,8]], [[4,3,8],[9,5,1],[2,7,6]],[[4,9,2],[3,5,7],[8,1,6]], [[6,1,8],[7,5,3],[2,9,4]],[[6,7,2],[1,5,9],[8,3,4]], [[8,1,6],[3,5,7],[4,9,2]],[[8,3,4],[1,5,9],[6,7,2]]]
ソースコード
import Data.List import Control.Monad.List shuffle :: [Int] -> [[Int]] shuffle [] = [[]] shuffle xs = do y <- xs ys <- shuffle (delete y xs) return (y:ys) same :: Eq a => [a] -> Bool same [] = True same (x:xs) = all (==x) xs magicSquare = do [a,b,c,d,e,f,g,h,i] <- shuffle [1..9] guard $ same [ a + b + c, d + e + f, g + h + i, a + d + g, b + e + h, c + f + i, a + e + i, c + e + g ] return [[a, b, c], [d, e, f], [g, h, i]]
