Duplicate Character Counter in Haskell

Duplicate Character

Counter in Haskell

Welcome to the Duplicate Character Counter in Haskell page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

{-# LANGUAGE TupleSections #-}

module Main where

import Data.Map (Map)
import qualified Data.Map.Strict as Map
import System.Environment (getArgs)

duplicateCharacters :: String -> Map Char Int
duplicateCharacters = Map.filter (> 1) . Map.fromListWith (+) . map (, 1)

printDuplicates :: String -> Map Char Int -> IO ()
printDuplicates []     _ = return ()
printDuplicates (x:xs) m =
  case Map.updateLookupWithKey (\_ _ -> Nothing) x m of
    (Just count, m') -> putStrLn (x : ": " ++ show count) >> printDuplicates xs m'
    _                -> printDuplicates xs m

main :: IO ()
main = do
  args <- getArgs
  case args of
    [xs@(_:_)] ->
      let m = duplicateCharacters xs
      in if Map.null m
          then putStrLn "No duplicate characters"
          else printDuplicates xs m
    _          -> putStrLn "Usage: please provide a string"

Duplicate Character Counter in Haskell was written by:

• Ricardo Mapurunga Junior

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

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How to Run the Solution

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