Haskell Quiz/PP Pascal/Solution Jethr0

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Example:

> pp_pascal 10
                 1
                1  1
              1  2  1
             1  3  3  1
           1  4  6  4  1
         1  5  10  10  5  1
       1  6  15  20  15  6  1
     1  7  21  35  35  21  7  1
   1  8  28  56  70  56  28  8  1
1  9  36  84  126  126  84  36  9  1

Solution:

pp_pascal n = unlines . map (center . showp) $ pascal
    where pascal   = take n $ iterate (\row -> zipWith (+) ([0] ++ row) (row ++ [0])) [1]
          showp    = concat . intersperse "  " . map show
          len      = length . showp $ last pascal
          center s = replicate ((len - (length s)) `div` 2) ' ' ++ s