http://tekkoc.tumblr.com/post/23802913135/10-haskell

gistfile1.hs

-- -*- coding: utf-8 -*-
import Test.HUnit

deal :: Int -> String -> [String]
deal n s = deal_ 0 (take n $ repeat "") (take ((length s) - (length s `mod` n)) s)
  where deal_ _ ys [] = ys
        deal_ m ys (x:xs) = deal_ ((m + 1) `mod` n) ((take m ys) ++ [(ys!!m) ++ [x]] ++ (drop (m + 1) ys)) xs

tests = test [
  ["111", "222", "333"] ~=? deal 3 "123123123",
  ["12", "23", "31","12"] ~=? deal 4 "123123123",
  ["000", "111", "222", "333", "444", "555"] ~=? deal 6 "012345012345012345",
  ["123", "123", "123", "123"] ~=? deal 4 "111122223333",
  ["012345012345012345"] ~=? deal 1 "012345012345012345",
  ["", "", "", "", "", ""] ~=? deal 6 "01234",
  ["", ""] ~=? deal 2 ""]

main = runTestTT tests