Haskell Quiz/PP Pascal/Solution Kelan

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Pretty basic solution. Find the biggest number the triangle will contain given the number of rows, use that number to determine column widths. Then just print out each row with the correct columns and spacing.

import System.Environment

nCr n r =
    ( product [ ( s + 1 ) .. n ] ) `div` ( product [ 2 .. t ] )
    where
    s = max r ( n - r )
    t = min r ( n - r )

-- maximum number in a pascal triangle
-- with given number of rows
trimax rows =
    nCr ( rows - 1 ) ( ( rows - 1 ) `div` 2 )

main = do
    args <- getArgs

    let rows = read . head $ args
        digits = 1 + ( truncate . logBase 10 . fromIntegral . trimax $ rows )
        pad s = ( replicate ( digits - length s ) ' ' ) ++ s
        for_ = flip mapM_

    for_ [ 0 .. ( rows - 1 ) ] $ \ n -> do
        putStr . concat . replicate ( rows - n - 1 ) . pad $ ""
        for_ [ 0 .. n ] $ \ r -> do
            putStr . pad . show . nCr n $ r
            putStr . pad $ ""
        putStrLn ""