Created
June 27, 2013 07:36
-
-
Save markus1189/5874644 to your computer and use it in GitHub Desktop.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
import Data.Maybe | |
import System.Environment | |
import Control.Applicative | |
import Control.Monad | |
import Control.Monad.Logic | |
type Queen = (Int,Int) | |
type Board = [Queen] | |
queens :: MonadPlus m => Int -> m Board | |
queens n = placeQueens n n | |
placeQueens :: MonadPlus m => Int -> Int -> m Board | |
placeQueens _ 0 = return mzero | |
placeQueens size k = do | |
queens' <- placeQueens size (k-1) | |
col <- msum [return x | x <-[1..size]] | |
let queen = (k,col) | |
guard $ queen `safeOn` queens' | |
return (queen:queens') | |
safeOn :: Queen -> Board -> Bool | |
safeOn q = not . any (inCheck q) | |
inCheck :: Queen -> Queen -> Bool | |
inCheck p1@(x1,y1) p2@(x2,y2) = x1 == x2 || y1 == y2 || p1 `isDiagonalTo` p2 | |
isDiagonalTo :: Queen -> Queen -> Bool | |
isDiagonalTo (x1,y1) (x2,y2) = abs (x1 - x2) == abs (y1 - y2) | |
main :: IO () | |
main = do | |
size <- maybe 8 read . listToMaybe <$> getArgs | |
printLines (queens size :: [Board]) | |
printLines . observeAll $ (queens size :: Logic Board) | |
where | |
printLines :: Show a => [a] -> IO () | |
printLines = putStrLn . unlines . fmap show |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment