Question

In Haskell How to write a function that receives a list and returns a list of...

In Haskell

How to write a function that receives a list and returns a list of tuples that contains the character and number of occurrence on the list.

for example: "Hello" -> [ ('H',1), ('e',1), ('l',2),('l',2),('o',1) ]

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Answer #1

Haskell code:

import Data.List

countOccurs :: String -> [(Char, Int)]
countOccurs str = map (\x -> (head x, length x)) $ group $ sort str

main = do
  str <- getLine
  print $ countOccurs str

Haskell code screenshot:

Output:

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