sudoku slover in Haskell (2)
继续精简haskell版的sudoku程序，稍微改了一下，这次用了8行，同时性能也提高了很多，对每个空格的所有解不是通过尝试算出来的，而是直接得出。
board = [0,3,4,1,7,0,5,0,0,
0,6,0,0,0,8,3,0,1,
7,0,0,3,0,0,0,0,6,
5,0,0,6,4,0,8,0,7,
0,1,0,9,0,0,0,6,0,
3,0,6,0,0,2,0,0,4,
8,0,0,0,0,9,0,0,2,
1,0,3,7,0,0,0,9,0,
0,0,9,0,3,1,7,4,0]
newboard xs ys = foldl (\acc x -> merge (break (==0) acc) x) xs ys where merge (f,0:t) x = f ++ [x] ++ t
pointget bd = [1..9] \\ [bd!!(x*9+y) | x<-[0..8], y<-[0..8], x==row||y==col||(f' x, f' y)==(f' row, f' col)] where
(row, col) = divMod (length (takeWhile (/=0) bd)) 9
f' x = x `div` 3 * 3
nextanswer answer = map (\x->answer++[x]) (pointget $ newboard board answer)
sudoku = (iterate (concatMap $ nextanswer) [[]]) !! length (filter (== 0) board)
divide bd = unfoldr (\x -> if x == [] then Nothing else Just (splitAt 9 x)) bd
main = mapM_ (\x -> putStrLn "answer:" >> mapM_ print (divide $ newboard board x) >> putStrLn "") sudoku
改天看看能否继续减少代码行数。