CIS194:hw3

module Golf where

import Data.List
import Data.Text (justifyRight, pack, unpack)
import Data.Ord (comparing)

-- ex 1
skips :: [a] -> [[a]]
skips xs = map (flip every xs) [1..length xs]

every :: Int -> [a] -> [a]
every n xs = case drop (n-1) xs of
               (y:ys) -> y : every n ys
               []     -> []

-- ex 2
localMaxima :: [Integer] -> [Integer]
localMaxima []    = []
localMaxima [x]   = []
localMaxima [x,y] = []
localMaxima (x:y:z:zs)
  | y > x && y > z = y : localMaxima (y:z:zs)
  | otherwise      = localMaxima (y:z:zs)

-- ex 3
histLine :: (Integer, Int) -> String
histLine (n, count) = replicate count '*' ++ "=" ++ show n

frequencies :: [Integer] -> [(Integer, Int)]
frequencies xs = map (\x -> (head x, length x)) . group . sort $ xs

pad :: [String] -> [String]
pad ss = map (\s -> unpack $ justifyRight maxLen ' ' $ pack s) ss
         where maxLen = length $ maximumBy (comparing length) ss

histogram :: [Integer] -> String
histogram [] = ""
histogram xs = unlines . transpose . pad $ map (\n -> case lookup n (frequencies xs) of
                                                        Just count -> histLine (n, count)
                                                        Nothing -> histLine (n, 0)) [0..9]