Difference between revisions of "99 questions/Solutions/12"

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We only need to map single instances of an element to a list containing only one element and multiple ones to a list containing the specified number of elements and concatenate these lists.
 
We only need to map single instances of an element to a list containing only one element and multiple ones to a list containing the specified number of elements and concatenate these lists.
   
A solution for the simpler encoding (as <haskell>[(Int, a)]</haskell>) from problem 10 can be given as:
+
A solution for the simpler encoding from problem 10 can be given as:
   
 
<haskell>
 
<haskell>

Revision as of 05:12, 11 May 2011

(**) Decode a run-length encoded list.

Given a run-length code list generated as specified in problem 11. Construct its uncompressed version.

decodeModified :: [ListItem a] -> [a]
decodeModified = concatMap decodeHelper
    where
      decodeHelper (Single x)     = [x]
      decodeHelper (Multiple n x) = replicate n x

We only need to map single instances of an element to a list containing only one element and multiple ones to a list containing the specified number of elements and concatenate these lists.

A solution for the simpler encoding from problem 10 can be given as:

decode :: [(Int, a)] -> [a]
decode = concatMap (uncurry replicate)