(Haskell) Run-Length Encoding in Haskell

By SnipBot | Published: July 28, 2011

Problem 10 of the famous 99 Problems. I got 99 problems, but a Lisp ain’t one.

  1. import Data.List
  2.  
  3. thing :: String
  4. thing = "aaaabccaadeeee"
  5.  
  6. – My attempt got me close enough to consider it solved.
  7. encode :: (Eq a) => [a] -> [(Int, [a])]
  8. encode xs =
  9.     let groupList = groupBy (\x y -> x == y) xs
  10.         lengths = map length groupList
  11.         letterList = map nub groupList
  12.     in zip lengths letterList
  13.    
  14. – from the haskell.org solutions:
  15. encode2 :: (Eq a) => [a] -> [(Int, a)]
  16. encode2 = map (\x -> (length x, head x)) . group
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