On 17-Sep-1999, Jan-Willem Maessen <[EMAIL PROTECTED]> wrote:
> I couldn't help but notice that the Haskell program to solve the given
> cryptarithm is very different indeed from the C++ or Mercury
> implementations. It selects from a set represented by a list (and
> does repeated list difference using \\) rather than generating and
> testing permutations.
Before I send that mail comparing Haskell/Mercury/C++, I tried a version of
the Haskell code that was much more closely analagous to the Mercury code.
But it actually ran slightly slower, so in my mail I only mentioned the
time for the original Haskell version.
Cheers,
Fergus.
P.S. Here's the Haskell code that is analagous to the Mercury code that
I posted.
import List
main = print answer
expand a b c d e f = f + e*10 + d*100 + c*1000 + b*10000 + a*100000
xs = [0,1..9] -- all the digits
answer = head [ list | list@[t,h,i,r,y,w,e,l,v,n] <- perm xs,
expand t h i r t y + 5 * expand t w e l v e == expand n i n e t y]
perm :: [t] -> [[t]]
perm [] = [[]]
perm (x:xs) = [(y:zs) | (y,ys) <- del (x:xs), zs <- perm ys]
del :: [t] -> [(t,[t])]
del [] = []
del (x:xs) = ((x,xs) : [ (y,(x:ys)) | (y,ys) <- del xs ])
--
Fergus Henderson <[EMAIL PROTECTED]> | "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh> | of excellence is a lethal habit"
PGP: finger [EMAIL PROTECTED] | -- the last words of T. S. Garp.
