[Haskell-cafe] Re: Function to detect duplicates
Ketil Malde
ketil at malde.org
Fri Feb 26 15:34:28 EST 2010
Daniel Fischer <daniel.is.fischer at web.de> skrev:
> Am Freitag 26 Februar 2010 16:50:42 schrieb Ketil Malde:
>>> solutions = [[x1,x2,x3,x4,x5,x6,x7,x8,x9,x10]
>>> | x1 <- [0..9]
> First digit can't be 0, so make it [1 .. 9].
> Since you use the fact that the last digit must be the 0, pull all others
> from [1 .. 9].
Originally, I pulled from alternating odds (x1 <- [1,3..9] etc) and
evens, since this is fairly easy to deduce... I reverted this since the
point was to use brute force.
>>> solve :: [Int] -> [[Int]]
>
> Not on a 32-bit system. Word would suffice there, but you don't know that
> in advance, so it'd be Int64 or Integer
Hm? The Ints are just individual digits here.
> I would make the length of the prefix a parameter of solve.
I thought about generating a list with solutions for increasing lenghts,
so that e.g. 'solve [] !! 10' would solve this particular problem.
> solve prefix =
> case length prefix of
> 10 -> return prefix
> l -> do
> x <- [0 .. 9]
> ...
>
> over the if-then-else.
Yes, much nicer. Thanks for the feedback!
-k
--
If I haven't seen further, it is by standing in the footprints of giants
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