On 7/17/07, James Hunt <[EMAIL PROTECTED]> wrote:
As a struggling newbie, I've started to try various exercises in order
to improve. I decided to try the latest Ruby Quiz
(http://www.rubyquiz.com/quiz131.html) in Haskell. Would someone be kind
enough to cast their eye over my code? I get the feeling there's a
better way of doing it!
subarrays :: [a] -> [[a]]
subarrays [] = [[]]
subarrays xs = (sa xs) ++ subarrays (tail xs)
where sa xs = [ys | n <- [1..length xs], ys <- [(take n xs)]]
Check out the functions in Data.List
inits :: [a] -> [[a]]
tails :: [a] -> [[a]]
also, in a list comprehension, rather than: ys <- [x] consider: let ys = x
in this specific case: [take n xs | n <- [1..length xs]] would be even better
(though using inits and tails to accomplish this would be best of all)
maxsubarrays :: [Integer] -> [Integer]
maxsubarrays xs = msa [] (subarrays xs)
where
msa m [] = m
msa m (x:xs)
| sum x > sum m = msa x xs
| otherwise = msa m xs
--for testing: should return [2, 5, -1, 3]
main = maxsubarrays [-1, 2, 5, -1, 3, -2, 1]
This problem lends itself to being solved with Dynamic Programming and
can be solved in a single pass of the input list. (Rather than supply
the answer I'll encourage you to seek it out)
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