knight's tour

knight.hs

import Debug.Trace
import Control.Monad
import qualified Data.Map as M
import qualified Data.Set as S

--tr a b = trace (a++show b) b
tr a b = b
flat=foldl (++) []
board=S.fromList $ flat $ map (\a -> map (\b -> (a,b)) [0..7]) [0..7]

mov=[(2,1),(1,2),(-1,2),(-2,1),(-2,-1),(-1,-2),(1,-2),(2,-1)]

mov' (x,y)=map (\(x',y')->(x+x',y+y')) mov

nboard board pos=if S.member pos board 
                 then [(pos,S.delete pos board)]
                 else []

knight=knight' (S.delete (0,0) board) (0,0)

knight' board pos
  |board == S.empty = [[pos]]
  |otherwise        = 
    let n = tr "n:" $ flat $ map (nboard board) $ mov' pos
      in tr "knight':" $ flat $ map (\(p,b)->map (pos:) (knight' b p)) n


  
main=do
  let res = head knight
  let v = zip [0..] res
  forM_ [0..7] $ \x->do
    forM_ [0..7] $ \y->do
      let t=head $ filter ((==(x,y)).snd) v
      putStr $ show $ fst t 
      putStr " "
    putStr "\n"