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March 28, 2016 12:34
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| import Data.List | |
| import Data.List.Split | |
| -- Exercise 1 Hopscotch | |
| skips :: [a] -> [[a]] | |
| skips xs = zipWith every [1..(length xs)] (repeat xs) where | |
| every n xs = extractBy orderedPairs where | |
| extractBy = fmap fst . filter ((== n) . snd) | |
| orderedPairs = zip xs $ cycle [1..n] | |
| -- every n xs = fmap (take 1 . reverse) . filter (\x -> length x == n) $ chunksOf n xs | |
| -- every n xs = case drop (n-1) xs of | |
| -- (y:ys) -> y : every n ys | |
| -- [] -> [] | |
| -- skips [] = [] | |
| -- skips xs = [xs] ++ [everySecond xs] ++ nths where | |
| -- everySecond (x:y:xs) = y : (everySecond xs) | |
| -- everySecond _ = [] | |
| -- nths = fmap (\x -> [x]) $ drop 2 xs | |
| exercise1 = do | |
| print $ skips "ABCD" == ["ABCD", "BD", "C", "D"] | |
| print $ skips "hello!" == ["hello!", "el!", "l!", "l", "o", "!"] | |
| print $ skips [1] == [[1]] | |
| print $ skips [True,False] == [[True,False], [False]] | |
| -- print $ skips [] == [] | |
| -- Exercise 2 Local maxima | |
| localMaxima :: [Integer] -> [Integer] | |
| localMaxima xs = foldMap maxima $ triples xs where | |
| triples xs = zip3 xs (drop 1 xs) (drop 2 xs) | |
| maxima (x,y,z) = if (x < y) && (y > z) then [y] else [] | |
| -- triples l@(x:xs) = [take 3 l] ++ triples xs | |
| -- triples _ = [] | |
| -- maxima (x:y:z:[]) = if (x < y) && (y > z) then [y] else [] | |
| -- maxima _ = [] | |
| exercise2 = do | |
| print $ localMaxima [2,9,5,6,1] == [9,6] | |
| print $ localMaxima [2,3,4,1,5] == [4] | |
| print $ localMaxima [1,2,3,4,5] == [] | |
| -- Exercise 3 Histogram | |
| histogram :: [Integer] -> String | |
| histogram nums = unlines . transpose $ reverse . createRow <$> occurrences where | |
| occurrences = (\(x:xs) -> (show x, length xs)) <$> (group . sort . (++ [0..9])) nums | |
| maxHeight = maximum $ snd <$> occurrences | |
| createRow (x,y) = concat $ legend ++ bar where | |
| legend = [x ++ "="] | |
| bar = take maxHeight (replicate y "*" ++ repeat " ") | |
| exercise3 = do | |
| putStrLn $ histogram [1,1,1,5] | |
| putStrLn $ histogram [1,4,5,4,6,6,3,4,2,4,9] | |
| main :: IO () | |
| main = do | |
| exercise1 | |
| exercise2 | |
| putStrLn "" | |
| exercise3 |
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