2007/10/15, Felipe Lessa <[EMAIL PROTECTED]>: > On 10/15/07, apfelmus <[EMAIL PROTECTED]> wrote: > > Of course, the solution is to first drop n elements and then take > > tails instead of dropping n elements every time. > > > > map (drop n) . tails = tails . drop n > > > > O(m*n) O(m) > > Nice identity. I'll remember this one. > > > With this, we can write a function that returns the last n elements of > > a list in O(m) time and O(n) space as > > > > lasts :: Int -> [a] -> [a] > > lasts n xs = head $ [x | (x,[]) <- zip (tails xs) (tails $ drop n xs)] > > > > and use it as a drop-in replacement > > > > main n = print . sum . map read . lasts n . lines =<< getContents > > But that's a a two-liner now heh =).
If we're talking about (more than one)-liners, isn't this simpler to read? Or is it just me lasts n xs = let (_,remn) = splitAt n xs in go xs remn go lag [] = lag go [] _ = error "shouldn't happen" go (l:ls) (x:xs) = go ls xs -- Daniil Elovkov _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
