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Haskell 99 Problems - Solutions to 11 and 12

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problem 11, modified run-length encoding
========================================
If an element has no duplicates, mark it as such.

Example:

encodeModified "aaaabccaadeeee"

[Multiple 4 'a',Single 'b',Multiple 2 'c',
Multiple 2 'a',Single 'd',Multiple 4 'e']

problem 12, Decode a run-length encoded list.
=============================================
Given a run-length code list generated as specified in problem 11. Construct its uncompressed version.

Example:

decodeModified
[Multiple 4 'a',Single 'b',Multiple 2 'c',
Multiple 2 'a',Single 'd',Multiple 4 'e']

"aaaabccaadeeee"

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  1. data EncodedElement a = Multiple Int a | Single a
  2.     deriving Show
  3.  
  4. encodeModified :: (Eq a) => [a] -> [EncodedElement a]    
  5. encodeModified = map (\x -> if (length x > 1) 
  6.                               then Multiple (length x) (head x) 
  7.                               else Single (head x)) . group
  8.  
  9.  
  10. decodeModified :: [EncodedElement a] -> [a]
  11. decodeModified = concatMap decode
  12.     where 
  13.         decode (Multiple n c) = replicate n c
  14.         decode (Single c)     = c : []

URL: http://www.haskell.org/haskellwiki/99_questions/11_to_20

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