[Haskell-cafe] Hamming's Problem
Jose Luis Reyes F.
jlareyes at cybercia.com
Thu Jan 17 08:00:23 EST 2008
Hi,
In exercise 2 of http://www.walenz.org/Dijkstra/page0145.html we need to
write a function that holds
(1) The value 1 is in the sequence
(2) If x and y are in the sequence, so is f(x,y), where f has the
properties
a. f(x,y) > x
b. (y1 > y2) => (f(x,y1)>f(x,y2))
This is a solution for this problem, but an inefficient one
hammingff :: [Integer]
hammingff = 1 : merge [ h x y | x <- hammingff, y <- hammingff ] [ h x y | y
<- hammingff, x <- hammingff ]
h x y = 2*x+3*y
merge :: (Ord a) => [a] -> [a] -> [a]
merge [] xs = xs
merge ys [] = ys
merge (x:xs) (y:ys) = case compare x y of
LT -> x : merge xs (y:ys)
GT -> y : merge (x:xs) ys
EQ -> x : merge xs ys
anybody has a better solution?.
Thanks
Jose
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