[Haskell-beginners] Longest common prefix of a list of lists

29 Apr 2011


      Hi,

For one of my toy project I had to find the longest common prefix of a list
of strings.
I figured, that this function should only work on list-structure, meaning it
should have type
...
longestCommonPrefix :: [[a]] -> [a]
Sadly the best I could come up with was using explicit recursion. It works
as far as I tested it, but I have the feeling that there's a better way to
do it.
Here is the code:
...
longestCommonPrefix :: Eq a => [[a]] -> [a]
longestCommonPrefix []   = []
longestCommonPrefix xss | any null xss = []
                                       | otherwise    = loop xss []
 where loop ::Eq b => [[b]] -> [b] -> [b]
           loop xss acc =
             let xs = concatMap (take 1) xss
             in if any (\x -> x /= head xs) (tail xs)
                 then reverse acc
                 else loop (map tail xss) (head xs : acc)

[Haskell-beginners] Longest common prefix of a list of lists

philipp siegmantel