# HG changeset patch
# User Markus Kaiser <markus.kaiser@in.tum.de>
# Date 1360183725 -3600
# Node ID 15e527f4b92e5a13d97bb2b00be4149228ee6cc8
# Parent  89feab98266f8484005b7799bfe01348033f548d
add some more examples to G14.2 (thanks Tobi)

diff -r 89feab98266f -r 15e527f4b92e exercises/src/Exercise_14.hs
--- a/exercises/src/Exercise_14.hs	Tue Feb 05 22:12:07 2013 +0100
+++ b/exercises/src/Exercise_14.hs	Wed Feb 06 21:48:45 2013 +0100
@@ -56,20 +56,61 @@
 {---------------------------------------------------------------------}
 {- Aufgabe G14.2 -}
 
+-- Beispiele zur Endrekursion
+sum1 :: Int -> Int
+sum1 0 = 0
+sum1 n = n + sum1 (n - 1)
+{-
+sum1 3 = 3 + sum1 2
+    sum1 2 = 2 + sum1 1
+        sum1 1 = 1 + sum1 0
+            sum1 0 = 0
+        sum1 1 = 1 + 0
+               = 1
+    sum1 2 = 2 + 1
+           = 3
+sum1 3 = 3 + 3
+       = 6
+-}
+
+sum2 :: Int -> Int
+sum2 = sum2_end 0
+    where
+        sum2_end acc 0 = acc
+        sum2_end acc n = sum2_end (acc + n) (n - 1)
+{-
+sum2 3 = sum2_end 0 3
+       = sum2_end 3 2
+       = sum2_end 5 1
+       = sum2_end 6 0
+       = 6
+
+-}
+
+
+-- Concats
+-- Nicht Endrekursiv
 concat' :: [[a]] -> [a]
 concat' [] = []
 concat' (xs:xss) = xs ++ concat' xss
 
-
+-- O(n)
 concat'' :: [[a]] -> [a]
-concat'' xss = go [] (reverse xss)
+concat'' yss = go [] (reverse yss)
     where
     go acc [] = acc
     go acc (xs:xss) = go (xs ++ acc) xss
 
-
+-- O(n^2)
 concat''' :: [[a]] -> [a]
-concat''' = foldr (++) []
+concat''' = go []
+    where
+    go acc [] = acc
+    go acc (xs:xss) = go (acc ++ xs) xss
+
+-- Mit Fold
+concat'''' :: [[a]] -> [a]
+concat'''' = foldr (++) []