Cassidy's Interview Question - Mar 09/03/2020

soln.hs

import qualified Data.List as List

listSum :: (Num a) => [a] -> a
listSum [] = 0
listSum xs = foldr (+) 0 xs

getLength :: (Num a) => [a] -> a
getLength xs = foldr (\_ acc -> acc + 1) 0 xs

myGroup :: (Num a, Eq a, Ord a) => [a] -> [(a, Int)]
myGroup xs = map (\x -> (List.head x, List.length x)) . List.group . List.sort $ xs

getFirst :: (a, Int) -> a
getFirst (x, y) = x

mean :: (Num a, Fractional a, Ord a) => [a] -> a
mean [] = 0
mean xs = (listSum xs) / (getLength xs)

median :: (Num a, Fractional a, Ord a) => [a] -> a
median [] = 0
median xs = do
  let sortedList = List.sort xs
  let listLen = List.length xs
  if even listLen
    then (sortedList !! (div listLen 2))
    else (sortedList !! (div (listLen+1) 2))

mode :: (Num a, Fractional a, Ord a) => [a] -> a
mode [] = 0
mode xs = getFirst . List.head . List.reverse . List.sortBy (\(_, c) (_, d) -> compare c d) . myGroup $ xs

getMeanMedianMode :: (Num a, Fractional a, Ord a) => [a] -> (a, a, a)
getMeanMedianMode xs = (mean xs, median xs, mode xs)

main :: IO()
main = do
  let list = [1,2,3,5,5,5,5,5,5,2,1,2,1]
  print (getMeanMedianMode list)