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Haskell Quiz/PP Pascal/Solution Kelan

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[[Category:Haskell Quiz solutions|PP Pascal]]
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.
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.

Revision as of 11:12, 13 January 2007

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 ""
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Category: Haskell Quiz solutions