99 questions/Solutions/6
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(Difference between revisions)
(Just wanted to post a solution using a fold.) |
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isPalindrome' [_] = True | isPalindrome' [_] = True | ||
isPalindrome' xs = (head xs) == (last xs) && (isPalindrome' $ init $ tail xs) | isPalindrome' xs = (head xs) == (last xs) && (isPalindrome' $ init $ tail xs) | ||
| + | </haskell> | ||
| + | |||
| + | 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. | ||
| + | |||
| + | <haskell> | ||
| + | isPalindrome'' :: (Eq a) => [a] -> Bool | ||
| + | isPalindrome'' xs = foldl (\acc (a,b) -> if a == b then acc else False) True input --just to be different | ||
| + | where | ||
| + | input = zip xs (reverse xs) | ||
</haskell> | </haskell> | ||
Revision as of 04:52, 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 --just to be different where input = zip xs (reverse xs)
