Golf.hs

{-
Exercise 1 Hopscotch
Your first task is to write a function

skips :: [a] -> [[a]]

The output of skips is a list of lists. The first list in the output should
be the same as the input list. The second list in the output should
contain every second element from the input list. . . and the nth list in
the output should contain every nth element from the input list.
For example:

skips "ABCD" == ["ABCD", "BD", "C", "D"]
skips "hello!" == ["hello!", "el!", "l!", "l", "o", "!"]
skips [1] == [[1]]
skips [True,False] == [[True,False], [False]]
skips [] == []

Note that the output should be the same length as the input.
-}


localMaxima :: [Integer] -> [Integer]
localMaxima [] = []
localMaxima [x] = []
localMaxima [x,y] = []
localMaxima (x:y:z:xs)
    | y > x && y > z = [y] ++ localMaxima (y:z:xs)
    | otherwise = localMaxima (y:z:xs)


histogram :: [Integer] -> String
histogram numbers =
    let initialcounts = take 10 (repeat 0)
        calculatedcounts = histogramcount numbers initialcounts
        maxheight = maximum calculatedcounts
        linefunctions = map drawline [maxheight..0]
    in unlines (map ($ calculatedcounts) linefunctions)

histogramcount :: [Integer] -> [Int] -> [Int]
histogramcount [] counts = counts
histogramcount (x:xs) counts =
    let
        xint = fromIntegral x
        newcount = (counts !! xint) + 1
    in histogramcount xs (take xint counts ++ [newcount] ++ drop (xint+1) counts)

drawline :: Int -> [Int] -> String
drawline level = map (\x -> if x >= level then '#' else ' ')