Hmmm... it seems that n=63 is a special case. oleg@okmij.org wrote:
Yes, there is a solution for n=99 and for n=100 for that matter -- which can be found under one second. I only had to make a trivial modification to the previously posted code
tour n k s b | k > n*n = return b | otherwise = do next <- (foldr mplus mzero).map return $ successors n b s tour n (k+1) next $ insrt next k b
I replaced foldl1 mplus with foldr mplus zero.
The old version sees no solution to n=63 quite quickly:
time nice ./fromwiki-63 63 fromwiki-63: Prelude.foldl1: empty list
real 0m0.285s user 0m0.172s sys 0m0.026s
The version with the 'tour' given above does not halt after running up to 0.4 GB of RAM, so I killed it. Though having no solution may be tied to starting in the corner. -- Chris