# Haskell Quiz/PP Pascal/Solution Kelan

### From HaskellWiki

< Haskell Quiz | PP Pascal(Difference between revisions)

(+cat) |
m |
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Line 4: | Line 4: | ||

<haskell> |
<haskell> |
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import System.Environment |
import System.Environment |
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+ | import Control.Monad (forM_) |
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nCr n r = |
nCr n r = |
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Line 22: | Line 23: | ||

digits = 1 + ( truncate . logBase 10 . fromIntegral . trimax $ rows ) |
digits = 1 + ( truncate . logBase 10 . fromIntegral . trimax $ rows ) |
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pad s = ( replicate ( digits - length s ) ' ' ) ++ s |
pad s = ( replicate ( digits - length s ) ' ' ) ++ s |
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− | for_ = flip mapM_ |
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− | for_ [ 0 .. ( rows - 1 ) ] $ \ n -> do |
+ | forM_ [ 0 .. ( rows - 1 ) ] $ \ n -> do |

putStr . concat . replicate ( rows - n - 1 ) . pad $ "" |
putStr . concat . replicate ( rows - n - 1 ) . pad $ "" |
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− | for_ [ 0 .. n ] $ \ r -> do |
+ | forM_ [ 0 .. n ] $ \ r -> do |

putStr . pad . show . nCr n $ r |
putStr . pad . show . nCr n $ r |
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putStr . pad $ "" |
putStr . pad $ "" |

## Latest revision as of 21:15, 14 December 2009

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