-----BEGIN PGP SIGNED MESSAGE----- Hash: RIPEMD160 Hi, I wrote a brute-force sudoku solver. It takes a [[Int]] and spits out the first solution it finds. Why is it, that [0,0,0,7,0,6,9,0,0] [9,0,0,0,0,4,7,0,0] [7,0,0,0,0,0,4,0,0] [0,2,7,0,3,5,8,0,0] [6,9,5,8,2,0,0,0,0] [0,8,0,0,0,0,5,0,0] [0,3,0,0,0,0,0,0,0] [8,7,0,9,0,0,0,0,0] [0,0,0,0,0,0,0,0,0] is solved instantly, but when I remove just one number my program takes forever? === import Array import List import System type Field = Array Int (Array Int Int) isEmpty :: Int -> Bool isEmpty = (==) 0 done :: Field -> Bool done a = isFull a && checkField a isFull::Field -> Bool isFull a = notElem (0) $ (concat.(map elems).elems) a readField :: [[Int]]->Field readField = (listArray (1,9).map (listArray (1,9))) checkField :: Field -> Bool checkField a = check (rows a) && check (columns a) && check (squares a) where check b = and $ ((map ((==1).length)).concat.(map group).clean) b clean = map (dropWhile isEmpty.sort) columns::Field -> [[Int]] columns a = [[a!i!j|i<-[1..9]]|j<-[1..9]] rows :: Field -> [[Int]] rows a = [[a!i!j|j<-[1..9]]|i<-[1..9]] squares :: Field -> [[Int]] squares a = [[a!(i+n)!(j+m)|i<-[1..3],j<-[1..3]] |n<-[0,3,6],m<-[0,3,6]] - -- creates a list of all allowed entries genMoves :: Field -> [Field] genMoves a = concat [update a i j|i<-[1..9],j<-[1..9],isEmpty (a!i!j)] where update b i j= [b //[(i,b!i //[(j,x)])]|x<-[1..9], checkField (b //[(i,b!i //[(j,x)])])] play :: [Field] -> Maybe Field play (f:a) | done f= Just f | isFull f= play a | otherwise = play ((genMoves f)++a) play [] = Nothing main :: IO () main = do x <- getArgs let field = read (x!!0) :: [[Int]] let erg=play [readField field] case erg of Just a -> putStrLn $ concat $ map ((++"\n").show) (rows a) Nothing -> putStrLn "Es gibt keine Loesung" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFGtx0r11V8mqIQMRsRA7P5AJ9lG3mF3fHpUiyOqCeRVOOEGozp1wCeI80C RfD/U5y+yEgF0fe+kRwDbUI= =Ngss -----END PGP SIGNATURE-----