Difference between revisions of "99 questions/Solutions/14"

Revision as of 03:55, 18 November 2010

(*) Duplicate the elements of a list.

dupli [] = []
dupli (x:xs) = x:x:dupli xs

or, using list comprehension syntax:

dupli list = concat [[x,x] | x <- list]

or, using the list monad:

dupli xs = xs >>= (\x -> [x,x])

or, using concatMap:

dupli = concatMap (\x -> [x,x])

also using concatMap:

dupli = concatMap (replicate 2)

or, using foldr:

dupli = foldr (\ x xs -> x : x : xs) []

@@ Line 17: / Line 17: @@
 </haskell>
-or, using concatMap:
+or, using <hask>concatMap</hask>:
 <haskell>
 dupli = concatMap (\x -> [x,x])
 </haskell>
-also using concatMap:
+also using <hask>concatMap</hask>:
 <haskell>
 dupli = concatMap (replicate 2)
 </haskell>
-or, using foldr:
+or, using <hask>foldr</hask>:
 <haskell>
 dupli = foldr (\ x xs -> x : x : xs) []