List comprehension seems like the easiest way to do it.
First here's how to get the cross product of two lists, I'll be using
this below:
cp as bs = [(x,y) | x <- as, y <- bs ]
-- cp [1,2,3] [4,5,6] = [(1,4),(1,5),(1,6),(2,4),(2,5),(2,6),(3,4),(3,5),(3,6)]
Then constrain the cross product to tuples where the sum is the given number:
sums i as bs = [(x,y) | x <- as, y <- bs, x + y == i]
-- sums 4 [1,2,3] [1,2,3] == [(1,3),(2,2),(3,1)]
Then check that the list of constrained sums is not empty:
sumCheck i as bs = not (null (sums i as bs))
-deech
On Mon, Jul 25, 2011 at 10:52 PM, Bryce Verdier
Hi all, I'm new to haskell, and I'm trying to get better with it. Recently I completed one of the challenges from Programming Praxis and I was wondering if people would be willing to spend some time and tell me how I could improve my code. Thanks in advance, Bryce Here is a link to the programming praxis: http://programmingpraxis.com/2011/07/19/sum-of-two-integers/ And here is my code: import Data.List import Data.Maybe sumCheck :: Int -> [Int] -> [Int] -> Maybe (Int, Int) sumCheck _ [] _ = Nothing sumCheck total (x:xs) ys = if total' == Nothing then sumCheck total xs ys else return (x, (ys !! ( fromJust total'))) where total' = (total - x) `elemIndex` ys
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