implemented recursive versions of pof2s and pd

1 files changed, 30 insertions, 8 deletions

diff --git a/AufgabeFFP1.hs b/AufgabeFFP1.hs
index 705dce1..648c773 100644
--- a/AufgabeFFP1.hs
+++ b/AufgabeFFP1.hs
@@ -1,24 +1,46 @@
 module AufgabeFFP1
 where
 
--- calculates 2^ with each element of the continuous list
+-------------------------------------------------------------------------------
+-- Helpers
+
+-- !! Index function for Integer-type
+get ::  [a] -> Integer -> a
+get (x:xs) 0 = x
+get (x:xs) n = get xs (n-1)
+
+
+-------------------------------------------------------------------------------
+
+-- recursive version
 pof2s :: [Integer]
-pof2s = map (2^) [0,1..]
+pof2s = 1:(map (2*) pof2s)
 
 -- alternate:
+-- calculates 2^ with each element of the continuous list
+-- pof2s :: [Integer]
+-- pof2s = map (2^) [0,1..]
+
+-- alternate 2:
 -- pof2s :: [Integer]
 -- pof2s = iterate (2*) 1
 
 -------------------------------------------------------------------------------
 
+-- recursive version:
+pd :: [[Integer]]
+pd = [1] : (zipWith (\x y -> zipWith (+) ([0]++x) (y++[0])) pd pd)
+
+-- alternate:
+-- pd :: [[Integer]]
+-- pd = iterate (\row -> zipWith (+) ([0] ++ row) (row ++ [0])) [1]
+
 -- iterate steps:
 -- (1) [1]
 -- (2) zipWith (+) ([0,1])     ([1,0])     = [1,1]
 -- (3) zipWith (+) ([0,1,1])   ([1,1,0])   = [1,2,1]
 -- (4) zipWith (+) ([0,1,2,1]) ([1,2,1,0]) = [1,3,3,1]
 -- ...
-pd :: [[Integer]]
-pd = iterate (\row -> zipWith (+) ([0] ++ row) (row ++ [0])) [1]
 
 -------------------------------------------------------------------------------
 
@@ -33,16 +55,16 @@ pd = iterate (\row -> zipWith (+) ([0] ++ row) (row ++ [0])) [1]
 -- ...
 -- (n) [pd !! (n-1) !! 0] ++ [pd !! (n-2) !! 1] ++ [pd !! (n-3) !! 2] ++ ...
 fibdiag :: Integer -> [Integer]
-fibdiag (n)
+fibdiag n
   | n <= 0 = []
-  | otherwise = map (\x -> pd !! (fromInteger n - x) !! (x - 1)) [1..count]
+  | otherwise = map (\x -> pd `get` (n-x) `get` (x-1)) [1..count]
   where
-    count = (fromInteger n + 1) `div` 2
+    count = (n + 1) `div` 2
 
 -------------------------------------------------------------------------------
 
 fibdiags :: [[Integer]]
-fibdiags = map (fibdiag) [1,2..]
+fibdiags = map (fibdiag) [1..]
 
 -------------------------------------------------------------------------------