Personal tools

99 questions/Solutions/6

From HaskellWiki

< 99 questions | Solutions(Difference between revisions)
Jump to: navigation, search
(Just wanted to post a solution using a fold.)
Line 16: Line 16:
 
<haskell>
 
<haskell>
 
isPalindrome'' :: (Eq a) => [a] -> Bool
 
isPalindrome'' :: (Eq a) => [a] -> Bool
isPalindrome'' xs = foldl (\acc (a,b) -> if a == b then acc else False) True input --just to be different
+
isPalindrome'' xs = foldl (\acc (a,b) -> if a == b then acc else False) True input
 
where
 
where
 
input = zip xs (reverse xs)
 
input = zip xs (reverse xs)

Revision as of 04:53, 28 February 2011

(*) Find out whether a list is a palindrome. A palindrome can be read forward or backward; e.g. (x a m a x).

isPalindrome :: (Eq a) => [a] -> Bool
isPalindrome xs = xs == (reverse xs)
isPalindrome' []  = True
isPalindrome' [_] = True
isPalindrome' xs  = (head xs) == (last xs) && (isPalindrome' $ init $ tail xs)

Here's one to show it done in a fold just for the fun of it. Do note that it is less efficient then the previous 2 though.

isPalindrome'' :: (Eq a) => [a] -> Bool
isPalindrome'' xs = foldl (\acc (a,b) -> if a == b then acc else False) True input
	where
	input = zip xs (reverse xs)