Discussion on: Write a script to identify an anagram

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Replies for: You don't need sort or multiply or any fancy stuff int[26] wordcount; //array containing encounter count of each character. for each char: c...

This is good. I adapted it to Haskell, recording letter frequencies in Maps/dictionaries. The Map data structure is already an instance of the Eq typeclass, so it was a one-liner to add the equality check:

import qualified Data.Map.Strict as M

-- incrementor for Map entries (used by Map's alter function)

inc Nothing = Just 1
inc (Just x) = Just (x+1)

-- produces a Map containing frequencies of elements in a given list (or Foldable)
-- e.g. a Map of frequencies of characters in a given word

frequencies :: (Foldable t, Ord k, Num a) => t k -> M.Map k a
frequencies = foldr (M.alter inc) M.empty

-- equality is already defined for Maps :)

isAnagram word1 word2 = frequencies word1 == frequencies word2