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  1. Practice
  2. Functional Programming
  3. Recursion
  4. Pascal's Triangle
  5. Discussions

Pascal's Triangle

  • mihassan + 2 comments

    I am using a trick where infinte series can be used to contruct the same series, similar to how fibonacci series is generated:

    fibs = 0 : 1 : zipWith (+) fibs (tail fibs)

    For pascal triangle, we start using the first row, and then use each row to calculate the next row.

    pascalTriangle = 
    [1] : map nextRow pascalTriangle
  where 
    nextRow = ([1] ++). (++ [1]). pairSum
    pairSum x = zipWith (+) x (tail x)

showPascalTriangle = 
    map listToString pascalTriangle
  where
    listToString = unwords. map show
    

main = getLine >>= putStrLn. unlines. flip take showPascalTriangle. read
    • QuomoZ + 1 comment

      Pretty much the same thing I did, minus self-recursive definition shenanigans:

      pascal = iterate ((++ [1]) . (1:) . (zipWith (+) =<< tail)) [1]
      • yolanvanderhorst + 1 comment

        Bases on your solutions and adding a bit of my own, I think this might be the shorstest way to solve this, using just the Prelude:

        main=interact$unlines.map (unwords.(map show)).flip take s.read
s=[1]:map ((1:).(++[1]).(zipWith (+)=<<tail)) s
        • QuomoZ + 0 comments

          I could come up with a shorter one, here is your s function without spaces:

          s=[1]:map((1:).(++[1]).(zipWith(+)=<<tail))s

          which is longer by 5 characters than:

          p=[1]:[1:zipWith(+)r t++[1]|r@(_:t)<-p]
    • murtaught + 0 comments

      Spectacular "pointless" style. I couldn't help but chuckled on 'flip'.