Floyd's triangle: Difference between revisions

Or as a partially populated matrix:

<lang haskell>import Control.Monad (join)

import Data.Matrix (Matrix, getElem, matrix, nrows, toLists)

--------------------- FLOYDS TRIANGLE --------------------

floyd :: Int -> Matrix (Maybe Int)

floyd n = matrix n n go

where

go (y, x)

| x > y = Nothing

| otherwise = Just (x + quot (pred y * y) 2)

--------------------------- TEST -------------------------

main :: IO ()

main = mapM_ putStrLn $ showFloyd . floyd <$> [5, 14]

------------------------- DISPLAY ------------------------

showFloyd :: Matrix (Maybe Int) -> String

showFloyd m =

(unlines . fmap unwords . toLists) $

go <$> m

where

go Nothing = ""

go (Just n) = padRight w (show n)

Just v = join getElem (nrows m) m

w = length (show v)

padRight :: Int -> String -> String

padRight n = (drop . length) <*> (replicate n ' ' <>)</lang>

{{Out}}

<pre> 1

2 3

4 5 6

7 8 9 10

11 12 13 14 15

1

2 3

4 5 6

7 8 9 10

11 12 13 14 15

16 17 18 19 20 21

22 23 24 25 26 27 28

29 30 31 32 33 34 35 36

37 38 39 40 41 42 43 44 45

46 47 48 49 50 51 52 53 54 55

56 57 58 59 60 61 62 63 64 65 66

67 68 69 70 71 72 73 74 75 76 77 78

79 80 81 82 83 84 85 86 87 88 89 90 91

92 93 94 95 96 97 98 99 100 101 102 103 104 105</pre>